From SILENT SPRING By Rachel Carson
A FABLE FOR TOMORROW
There was once a town in the heart of America where all life seemed to live in harmony with its surroundings. The town lay in the midst of a checkerboard of prosperous farms, with fields of grain and hillsides of orchards where, in spring, white clouds of bloom drifted above the green fields. In autumn, oak and maple and birch set up a blaze of color that flamed and flickered across a backdrop of pines. Then foxes barked in the hills and deer silently crossed the fields, half hidden in the mists of the fall mornings. Along the roads, laurel, viburnum and alder, great ferns and wildflowers delighted the traveler’s eye through much of the year.
Even in winter the roadsides were places of beauty, where countless birds came to feed on the berries and on the seed heads of the dried weeds rising above the snow. The countryside was, in fact, famous for the abundance and variety of its bird life, and when the flood of migrants was pouring through in spring and fall people traveled from great distances to observe them. Others came to fish the streams, which flowed clear and cold out of the hills and contained shady pools where trout lay. So it had been from the days many years ago when the first settlers raised their houses, sank their wells, and built their barns.
Then a strange blight crept over the area and everything began to change. Some evil spell had settled on the community: mysterious maladies swept the flocks of chickens; the cattle and sheep sickened and died. Everywhere was a shadow of death. The farmers spoke of much illness among their families. In the town the doctors had become more and more puzzled by new kinds of sickness appearing among their patients. There had been several sudden and unexplained deaths, not only among adults but even among children, who would be stricken suddenly while at play and die within a few hours.
There was a strange stillness. The birds, for example where had they gone? Many people spoke of them, puzzled and disturbed. The feeding stations in the backyards were deserted. The few birds seen anywhere were moribund; they trembled violently and could not fly. It was a spring without voices. On the mornings that had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices there was now no sound; only silence lay over the fields and woods and marsh.
On the farms the hens brooded, but no chicks hatched. The farmers complained that they were unable to raise any pigs the litters were small and the young survived only a few days. The apple trees were coming into bloom but no bees droned among the blossoms, so there was no pollination and there would be no fruit.
The roadsides, once so attractive, were now lined with browned and withered vegetation as though swept by fire. These, too, were silent, deserted by all living things. Even the streams were now lifeless. Anglers no longer visited them, for all the fish had died.
In the gutters under the eaves and between the shingles of the roofs, a white granular powder still showed a few patches; some weeks before it had fallen like snow upon the roofs and the lawns, the fields and streams.
No witchcraft, no enemy action had silenced the rebirth of new life in this stricken world. The people had done it them selves.
This town does not actually exist, but it might easily have a thousand counterparts in America or elsewhere in the world. I know of no community that has experienced all the misfortunes I describe. Yet every one of these disasters has actually happened somewhere, and many real communities have already suffered a substantial number of them. A grim specter has crept upon us almost unnoticed, and this imagined tragedy may easily become a stark reality we all shall know.
What has already silenced the voices of spring in countless towns in America? This book is an attempt to explain.
The Obligation to Endure
The most alarming of all man’s assaults upon the environment is the contamination of air, earth, rivers, and sea with dangerous and even lethal materials. This pollution is for the most part irrecoverable; the chain of evil it initiates not only in the world that must support life but in living tissues is for the most part irreversible. In this now universal contam ination of the environment, chemicals are the sinister and little recognized partners of radiation in changing the very nature of the world the very nature of its life. Strontium go, re leased through nuclear explosions into the air, comes to earth in rain or drifts down as fallout, lodges in soil enters into the grass or corn or wheat grown there, and in time takes up its abode in the bones of a human being, there to remain until his death. Similarly, chemicals sprayed on croplands or forests or gardens lie long in soil,, entering into living organisms, passing from one to another in a chain of poisoning and death. Or they pass mysteriously by underground streams until they emerge and, through the alchemy of air and sunlight, combine into new forms that kill vegetation, sicken cattle, and work unknown liarm on those who drink from once pure wells. As Albert Schweitzer has said, “Man can hardly even recognize the devils of his own creation.”
It took hundreds of millions of years to produce the life that now inhabits the earth eons of time in which that developing and evolving and diversifying life reached a state of adjustment and balance with its surroundings. The environ ment, rigorously shaping and directing the life it supported, contained elements that were hostile as well as supporting. Cer tain rocks gave out dangerous radiation; even within the light of the sun, from which all life draws its energy, there were shortwave radiations with power to injure. Given time time not in years but in millennia life adjusts, and a balance has been reached. For time is the essential ingredient; but in the modern world there is no time.
The rapidity of change and the speed with which new situa tions are created follow the impetuous and heedless pace of man rather than the deliberate pace of nature. Radiation is no longer merely the background radiation of rocks, the bombardment of cosmic rays, the ultraviolet of the sun that have existed before there was any life on earth; radiation is now the unnatural crea tion of man’s tampering with the atom. The chemicals to which life is asked to make its adjustment are no longer merely the calcium and silica and copper and all the rest of the minerals washed out of the rocks and carried in rivers to the sea; they are the synthetic creations of man’s inventive mind, brewed in his laboratories, and having no counterparts in nature.
To adjust to these chemicals would require time on the scale that is nature’s; it would require not merely the years of a man’s life but the life of generations. And even this, were it by some miracle possible, would be futile, for the new chemicals come from our laboratories in an endless stream; almost five hundred annually find their way into actual use in the United States alone. The figure is staggering and its implications are not easily grasped 5oo new chemicals to which the bodies of men and animals are required somehow to adapt each year, chemicals totally outside the limits of biologic experience.
Among them are many that are used in man’s war against nature. Since the midi940’s over 2oo basic chemicals have been created for use in killing insects, weeds, rodents, and other organisms described in the modern vernacular as “pests”; and they are sold under several thousand different brand names. These sprays, dusts, and aerosols are now applied almost uni versally to farms, gardens, forests, and homesnonselective chemicals that have the power to kill every insect, the “good” and the “bad,” to still the song of birds and the leaping of fish in the streams, to coat the leaves with a deadly film, and to linger on in soil all this though the intended target may be only a few weeds or insects. Can anyone believe it is possible to lay down such a barrage of poisons on the surface of the earth without making it unfit for all life? They should not be called “insecticides,” but “biocides.”
The whole process of spraying seems caught up in an endless spiral. Since DDT was released for civilian use, a process of escalation has been going on in which ever more toxic materials must be found. This has happened because insects, in a trium phant vindication of Darwin’s principle of the survival of the fittest, have evolved super races immune to the particular in secticide used, hence a deadlier one has always to be developed and then a deadlier one than that. It has happened also be cause, for reasons to be described later, destructive insects often undergo a “flareback,” or resurgence, after spraying, in numbers greater than before. Thus the chemical war is never won, and all life is caught in its violent crossfire. Along with the possibility of the extinction of mankind by nuclear war, the central problem of our age has therefore be come the contamination of man’s total environment with such substances of incredible potential for harmsubstances that accumulate in the tissues of plants and animals and even pene trate the germ cells to shatter or alter the very material of heredity upon which the shape of the future depends.
Some wouldbe architects of our future look toward a time when it will be possible to alter the human germ plasm by design. But we may easily be doing so now by inadvertence, for many chemicals, like radiation, bring about gene mutations. It is ironic to think that man might determine his own future by something so seemingly trivial as the choice of an insect spray.
All this has been riskedfor what? Future historians may well be amazed by our distorted sense of proportion. How could intelligent beings seek to control a few unwanted species by a method that contaminated the entire environment and brought the threat of disease and death even to their own kind? Yet this is precisely what we have done. We have done it, moreover, for reasons that collapse the moment we examine them. We are told that the enormous and expanding use of pesticides is necessary to maintain farm production. Yet is our real problem not one of overproduction,? Our farms, despite measures to remove acreages from production and to pay farmers not to produce, have yielded such a staggering excess of crops that the American taxpayer in i962 is paying out more than one billion dollars a year as the total carrying cost of the surplusfood storage program. And is the situation helped when one branch of the Agriculture Department tries to reduce production while another states, as it did in i958, “It is believed generally that reduction of crop acreages under provisions of the Soil Bank will stimulate interest in use of chemicals to obtain maximum production on the land retained in crops.”
All this is not to say there is no insect problem and no need of control. I am saying, rather, that control must he geared to realities, not to mythical situations, and that the methods em ployed must be such that they do not destroy us along with the insects.
The problem whose attempted solution has brought such a train of disaster in its wake is an accompaniment of our modern way of life. Long before the age of man, insects inhabited the earth a group of extraordinarily varied and adaptable beings. Over the course of time since man’s advent, a small percentage of the more than half a million species of insects have come into conflict with human welfare in two principal ways: as competitors for the food supply and as carriers of human disease.
Diseasecarrying insects become important where human be ings are crowded together, especially under conditions where sanitation is poor, as in time of natural disaster or war or in situations of extreme poverty and deprivation. Then control of some sort becomes necessary. It is a sobering fact, however, as we shall presently see, that the method of massive chemical control has had only limited success, and also threatens to worsen the very conditions it is intended to curb.
Under primitive agricultural conditions the farmer had few insect problems. These arose with the intensification of agricul ture the devotion of immense acreages to a single crop. Such a system set the stage for explosive increases in specific insect populations. Singlecrop farming does not take advantage of the principles by which nature works; it is agriculture as an engineer might conceive it to be. Nature has introduced great variety into the landscape, but man has displayed a passion for simplifying it. Thus he undoes the builtin checks and balances by which nature holds the species within bounds. One impor tant natural check is a limit on the amount of suitable habitat for each species. Obviously then, an insect that lives on wheat can build up its population to much higher levels on a farm devoted to wheat than on one in which wheat is intermingled with other crops to which the insect is not adapted.
The same thing happens in other situations. A generation or more ago, the towns of large areas of the United States lined their streets with the noble elm tree. Now the beauty they hopefully created is threatened with complete destruction as disease sweeps through the elms, carried by a beetle that would have only limited chance to build up large populations and to spread from tree to tree if the elms were only occasional trees in a richly diversified planting. Another factor in the modern insect problem is one that must be viewed against a background of geologic and human history: the spreading of thousands of different kinds of organisms from their native homes to invade new territories. This worldwide migration has been studied and graphically described by the British ecologist Charles Elton in his recent book The Ecology of Invasions. During the Cretaceous Period, some hundred mil lion years ago, flooding seas cut many land bridges between continents and living things found themselves confined in what Elton calls “colossal separate nature reserves.” There, isolated from others of their kind, they developed many new species. When some of the land masses were joined again, about I 5 million years ago, these species began to move out into new territories a movement that is not only still in progress but is now receiving considerable assistance from man.
The importation of plants is the primary agent in the modern spread of species, for animals have almost invariably gone along with the plants, quarantine being a comparatively recent and not completely effective innovation. The United States Office of Plant Introduction alone has introduced almost 2oo,ooo species and varieties of plants from all over the world. Nearly half of the i8o or so major insect enemies of plants in the United States are accidental imports from abroad, and most of them have come as hitchhikers on plants.
In new territory, out of reach of the restraining hand of the natural enemies that kept down its numbers in its native land, an invading plant or animal is able to become enormously abundant. Thus it is no accident that our most troublesome insects are introduced species.
These invasions, both the naturally occurring and those de pendent on human assistance, are likely to continue indefinitely’ Quarantine and massive chemical campaigns are only extremely expensive ways of buying titne. We are faced, according to Dr. Elton, “with a lifean’ddeath need not just to find new technological means of suppressing this plant or that animal”; instead we need the basic knowledge of animal populations and their relations to their surroundings that will “promote an even balance and damp down the explosive power of outbreaks and new invasions.”
Much of the necessary knowledge is now available but we do not use it. We train ecologists in our universities and even employ them in our governmental agencies but we seldom take their advice. We allow the chemical dtath rain to fall as though there,were no alternative, whereas in fact there are many, and our ingenuity could soon discover many more if given opportunity.
Have we fallen into a mesmerized state that makes us accept as inevitable that which is inferior or detrimental, as though having lost the will or the vision to demand that which is good? Such thinking, in the words of the ecologist Paul Shepard, “Idealizes life with only its head out of water, inches above the limits of toleration of the corruption of its own environment … Why should we tolerate a diet of weak poisons, a home in insipid surroundings, a circle of acquaintances who are not quite our enemies, the noise of motors with just enough relief to pre vent insanity? Who would want to live in a world which is just not quite fatal?”
Yet such a world is pressed upon us. The crusade to create a chemically sterile, insectfree world seems to have engendered a fanatic zeal on the part of many specialists and most of the socalled control agencies. On every hand there is evidence that those engaged in spraying operations exercise a ruthless power. “The regulatory entomologists … function as prosecutor, judge and jury, tax assessor and collector and sheriff to enforce their own orders,” said Connecticut entomologist Neely Turner. The most flagrant abuses go unchecked in both state and federal agencies.
It is not my contention that chemical insecticides must never be used. I do contend that we have put poisonous and biologically potent chemicals indiscriminately into the hands of per sons largely or wholly ignorant of their potentials for harm. We have subjected enormous numbers of people to contact with these poisons, without their consent and often without their knowledge. If the Bill of Rights contains no guarantee that a citizen shall be secure against lethal poisons distributed either by private individuals or by public officials, it is surely only because our forefathers, despite their considerable wisdom and foresight, could conceive of no such problem.
I contend, furthermore, that we have allowed these chemicals to be used with little or no advance investigation of their effect on soil, water, wildlife, and man himself. Future generations are unlikely to condone our lack of prudent concern for the integrity of the natural world that supports all life.
There is still very limited awareness of the nature of the threat. This is an era of specialists, each of whom sees his own problem and is unaware of or intolerant of the larger frame into which it fits. It is also an era dominated by industry, in which the right to make a dollar at whatever cost is seldom challenged. When the public protests, confronted with some obvious evi dence of damaging results of pesticide applications, it is fed little tranquilizing pills of half truth. We urgently need an end to these false assurances, to the sugar coating of unpalatable facts. It is the public that is being asked to assume the risks that the insect controllers calculate. The public must decide whether it wishes to continue on the present road, and it can do so only when in full possession of the facts. In the words of Jean Rostand, “The obligation to endure gives us the right to know.”
Surface Waters & Underground Seas
Of all our natural resources water has become the most precious. By far the greater part of the earth’s surface is covered by its enveloping seas, yet in the midst of this plenty we are in want. By a strange paradox, most of the earth’s abundant water is not usable for agriculture, industry, or human consumption because of its heavy load of sea salts, and so most of the world’s population is either experiencing or is threatened with critical shortages. In an age when man has forgotten his origins and is blind even to his most essential needs for survival, water along with other resources has become the victim of his indifference.
The problem of water pollution by pesticides can be under stood only in context, as part of the whole to which it belongs the pollution of the total environment of mankind. The pollution entering our waterways comes from many sources: radio active wastes from reactors, laboratories, and hospitals; fallout from nuclear explosions; domestic wastes from cities and towns; chemical wastes from factories. To these is added a new kind of fallout the chemical sprays applied to croplands and gar dens, forests and fields. Many of the chemical agents in this alarming melange imitate and augment the harmful effects of radiation, and within the groups of chemicals themselves there are sinister and littleunderstood interactions, transformations, and summations of effect.
Ever since chemists began to manufacture substances that nature never invented, the problems of water purification have become complex and the danger to users of water has increased..
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Yet these fish, too, contained DDT. Had the chemical reached this remote creek by hidden under ground streams? Or had it been airborne, drifting down as fallout oii the surface of the creek? In still another compar tive study, DDT was found in the tissues of fish from a @atch cry where the water supply originated in a deep ‘well. Again there was no record of local spraying. The only possible means of contamination seemed to be by means of groundwater.
In the entire waterpollution problem, there is probably noth ing more disturbing than the threat of widespread contamination of groundwater. It is not possible to add pesticides to water anywhere without threatening the purity of water everywhere. Seldom if ever does Nature operate in closed and separate compartments, and she has not done so in distributing the earth’s water supply. Rain, falling on the land, settles down through pores and cracks in soil and rock, penetrating deeper and deeper until eventually it reaches a zone where all the pores of the rock are filled with water, a dark, subsurface sea, rising under hills, sinking bene ath valleys. This groundwater is always on the move, sometimes at a pace so slow that it travels no more than 5o feet a year, sometimes rapidly, by comparison, so that it moves nearly a tenth of a mile in a day. It travels by unseen waterways until here and there it comes to the surface as a spring, or perhaps it is tapped to feed a well. But mostly it con tribute, to streams and so to rivers. Except for what enters streams directly as rain or surface runoff, all the running water of the earth’s surface was at one time groundwater. And so, in a very real and frightening sense, pollution of the ground water is pollution of water everywhere.
It must have been by such a dark, underground sea that poisonous chemicals traveled from a manufacturing plant in Colorado to a farming district several miles away, there to poison wells, sicken humans and livestock, and damage crops an extraordinary episode that may easily be only the first of many like it. Its history, in brief, is this. In 1943, the Rocky Mountain Arsenal of the Army Chemical Corps, located near Denver, began to manufacture war materials. Eight years later the facili ties of the arsenal were leased to a private oil company for the production of insecticides. Even before the change of opera tions, however, mysterious reports had begun to come in. Farmers several miles from the plant began to report unex plained sickness among livestock; they complained of extensive crop damage. Foliage turned yellow, plants failed to mature, and many crops were killed outright, There were reports of human illness, thought by some to be related.
The irrigation waters on these farms were derived from shallow wells. When the well waters were examined (in a study in1958, in which several state and federal agencies participated) they were found to contain an assortment of chemicals. Chlorides, chlorates, salts of phosphonic acid, fluorides, and arsenic had been discharged from the Rocky Mountain Arsenal into holding ponds during the years of its operation. Apparently the groundwater between the arsenal and the farms had become contaminated and it had taken 7 to 8 years for the wastes to travel underground a distance of about 3 miles from the holding ponds to the nearest farm. This seepage had continued to spread and had further contaminated an area of unknown extent. The investigators knew of no way to contain the contamination or halt its advance.
All this was bad enough, but the most mysterious and probably in the long run the most significant feature of the whole episode was the discovery of the weed killer 2,4D in some of the wells and in the holding ponds of the arsenal. Certainly its presence was enough to account for the damage to crops irrigated with this water. But the mystery lay in the fact that no 2,4D had been manufactured at the arsenal at any stage of its operations.
A disturbing example of (contamination of the surface waters )seems to be building up on the national wildlife refuges at Tule Lake and Lower Klamath, both in California. These refuges are part of a chain including also the refuge on Upper Klamath Lake just over the border ‘in Oregon. All are linked, perhaps fatefully, by a shared water supply, and all are affected by the fact that they lie like small islands in a great sea of sur rounding farmlands land reclaimed by drainage and stream diversion from an original waterfowl paradise of marshiand and open water. These farmlands around the refuges are now irrigated by water from Upper Klamath Lake. The irrigation waters, re collected from the fields they have served, are then pumped into Tule Lake and from there to Lower Klamath. All of the waters of the wildlife refuges established on these two bodies of water therefore represent the drainage of agricultural lands. It is important to remember this in connection with recent happenings.
In the summer of ig6o the refuge staff picked up hundreds of dead and dying birds at Tute Lake and Lower Klamath. Most of them were fisheating species herons, pelicans, grebes, gulls. Upon analysis, they were found to contain insecticide residues identified as toxaphene, DDD, and DDE. Fish from the lakes were also found to contain insecticides; so did samples of plankton. The refuge manager believes that pesticide residues are now building up in the waters of these refuges, being conveyed there by return irrigation flow from heavily sprayed agricultural lands.
Such poisoning of waters set aside for conservation purposes could have consequences felt by every western duck hunter and by everyone to whom the sight and sound of drifting ribbons of waterfowl across an evening sky are precious. These particular refuges occupy critical positions in the conservation of west ern waterfowl. They lie at a point corresponding to the narrow neck of a funnel, into which all the migratory paths composing what is known as the Pacific Flyway converge. During the fall migration they receive many millions of ducks and geese from nesting grounds extending from the shores of Bering Sea east to Hudson Bay fully three fourths of all the waterfowl that move south into the Pacific Coast states in autumn. In summer they provide nesting areas for waterfowl, especially for two endangered species, the redhead and the ruddy duck. If the lakes and pools of these refuges become seriously contaminated, the damage to the waterfowl populations of the Far West could be irreparable. Water must also be thought of in terms of the chains of life it supports from the smallasdust green cells of the drifting plant plankton, through the minute water fleas to the fishes that strain plankton from the water and are in turn eaten by other fishes or by birds, mink, raccoons in an endless cyclic trans fer of materials from life to life. We know that the necessary rninerals in the water .ire so passed from link to link of the food chains. Can we suppose that poisons we introduce into water will not also enter into these cycles of nature?
The answer is to be found in the amazing history of Clear Lake, California. Clear Lake ties in mountainous country some ‘les north of San Francisco and has long been popular with go ml anglers. The name is inappropriate, for actually it is a rather turbid lake because of the soft black ooze that covers its shallow bottom. Unfortunately for the fishermen and the resort dwell ers on its shores, its waters have provided an ideal habitat for a small gnat, Cbaoboius astictopus. Although closely related to mosquitoes, the gnat is not a bloodsucker and probably does not feed at all as an adult. However, human beings who shared its habitat found it annoying because of its sheer numbers. Efforts were made to control it but they were largely fruitless until, in the late 1940’s, the chlorinated hydrocarbon insecticides offered new weapons. The chemical chosen for a fresh attack was DDD, a close relative of DDT but apparently offering fewer threats to fish life.
The new control measures undertaken in 1949 were carefully planned and few people would have supposed any harm could result. The lake was surveyed, its volume determined, and the insecticide applied in such great dilution that for every part of chemical there would be 70 million parts of water. Control of the gnats was at first good, but by 1954 the treatment had to be repeated, this time at the rate of I part of insecticide in 5o mil lion parts of water. The destruction of the gnats was thought to be virtually complete.
The following winter months brought the first intimation that other life was affected: the western grebes on the lake began to die, and soon ignore than a hundred of them were reported dead. At Clear Lake the western grebe is a breeding bird and also a winter visitant, attracted by the abundant fish of the lake. It is a bird of spectacular appearance and beguiling habits, build ing its floating nests in shallow lakes of western United States and Canada. It is called the “swan grebe” with reason, for it glides with scarcely a ripple across the lake surface, the body riding low, white neck and shining black head held high. The newly hatched chick is clothed in soft gray down; in only a few hours it takes to the water and rides on the back of the father or mother, nestled under the parental wing coverts.
Following a third assault on the everresilient gnat population, in 1957, more grebes died. As had been true in1954, no evidence of infectious disease could be discovered on examination of the dead birds. But when someone thought to analyze the fatty tissues of the grebes, they were found to be loaded with DDD in the extraordinary concentration of i6oo parts per million. The maximum concentration applied to the water was 1/5o part per million. How could the chemical have built up to such prodigious levels in the grebes? These birds, of course, are fish eaters. When the fish of Clear Lake also were analyzed the picture began to take form the poison being picked up by the smallest organisms, concentrated and passed on to the larger.
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Here the problem was resolved in favor of those annoyed by gnats, and at the expense of an unstated, and probably not even clearly understood, risk to all who took food or water from the lake.
It is an extraordinary fact that the deliberate introduction of poisons into a reservoir is becoming a fairly common practice. The purpose is usually to promote recreational uses, even though the water must then be treated at some expense to make it fit for its intended use as drinking water. When sportsmen of an area want to “improve” fishing in a reservoir, they prevail on authorities to dump quantities of poison into it to kill the un desired fish, which are then replaced with hatchery fish more suited to the sportsmen’s taste. The procedure has a strange, AliceinWonderland quality. The reservoir was created as a public water supply, yet the community, probably unconsulted about the sportsmen’s project, is forced either to drink water containing poisonous residues or to pay out tax money for treatment of the water to remove the poisons treatments that are by no means foolproof.
As ground and surface waters are contaminated with pesticides and other chemicals, there is danger that not only poisonous but also cancerproducing substances are being introduced into public water supplies. Dr. W. C. Hueper of the National Cancer Institute has warned that “the danger of cancer hazards from the consumption of contaminated drinking water will grow considerably within the foreseeable future.” And indeed a study made in Holland in the early 195o’s provides support for the view that polluted waterways may carry a cancer hazard. Cities receiving their drinking water from rivers had a higher death rate from cancer than did those whose water caine from sources presumably less susceptible to pollution such as wells. Arsenic, the environmental substance most clearly es tablished as causing cancer in man, is involved in two historic cases in which polluted water supplies caused widespread oc currence of cancer. In one case the arsenic came from the slag heaps of mining operations, in the other from rock with a high natural content of arsenic. These conditions may easily be duplicated as a result of heavy applications of arsenical in secticides. The soil in such areas becomes poisoned. Rains then carry part of the arsenic into streams, rivers, and reservoirs, as well as into the vast subterranean seas of groundwater. Here again we are reminded that in nature nothing exists alone. To understand more clearly how the pollution of our world is happening, we must now look at another of the earth’s basic resources, the soil.
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Here the problem was resolved in favor of those annoyed by gnats, and at the expense of an Cities receiving their drinking water from rivers had a higher death rate from cancer than did those whose water caine from sources presumably less susceptible to pollution such as wells. Arsenic, the environmental substance most clearly established as causing cancer in man, is involved in two historic cases in which polluted water supplies caused widespread occurrence of cancer. In one case the arsenic came from the slag heaps of mining operations, in the other from rock with a high natural content of arsenic. These conditions may easily be duplicated as a result of heavy applications of arsenical in secticides. The soil in such areas becomes poisoned. Rains then carry part of the arsenic into streams, rivers, and reservoirs, as well as into the vast subterranean seas of groundwater. Here again we are reminded that in nature nothing exists alone. To understand more clearly how the pollution of our world is happening, we must now look at another of the earth’s basic resources, the soil. ~
THE OTHER ROAD
278 The choice, after all, is ours to make. If, having endured much, we have at last asserted our “right to know,” and if, knowing, we have concluded that we are being asked to take senseless and frightening risks, then we should no longer accept the counsel of those who tell us that we must fill our world with poisonous chemicals; we should look about and see what other course is open to us.
A truly extraordinary variety of alternatives to the chemical control of insects is available. Some are already in use and have achieved brilliant success. Others are in the stage of laboratory testing. Still others are little more than ideas in the minds of imaginative scientists, waiting for the opportunity to put them to the test. All have this in common: they are biological solu tions, based on understanding of the living organisms they seek to control, and of the whole fabric of life to which these organ isms belong. Specialists representing various areas of the vast field of biology are contributing entomologists, pathologists, geneticists, physiologists, biochemists, ecologists all pouring their knowledge and their creative inspirations into the forma tion of a new science of biotic controls.
“Any science may be likened to a river,” says a Johns Hopkins biologist, Professor Carl P. Swanson. “It has its obscure and unpretentious beginning; its quiet stretches as well as its rapids; its periods of drought as well as of fullness. It gathers momentum with the work of many investigators and as it is fed by other streams of thought; it is deepened and broadened by the concepts and generalizations that are gradually evolved.”
So it is with the science of biological control in its modern sense. In America it had its obscure beginnings a century ago with the first attempts to introduce natural enemies of insects that were proving troublesome to farmers, an effort that some times moved slowly or not at all, but now and again gathered speed and momentum under the impetus of an outstanding suc cess. It had its period of drought when workers in applied entomology, dazzled by the spectacular new insecticides of the 194o’s, turned their backs on all biological methods and set foot on “the treadmill of chemical control.” But the goal of an insectfree world continued to recede. Now at last, as it has become apparent that the heedless and unrestrained use of chemi cals is a greater menace to ourselves than to the targets, the river which is the science of biotic control flows again, fed by new streams of thought.
Some of the most fascinating of the new methods are those that seek to turn the strength of a species against itself to use the drive of an insect’s life forces to destroy it. The most spec tacular of these approaches is the “male sterilization” technique developed by the chief of the United States Department of Agriculture’s Entomology Research Branch, Dr. Edward Knipling, and his associates.
About a quarter of a century ago Dr. Knipling startled his colleagues by proposing a unique method of insect control. If it were possible to sterilize and release large numbers of insects, he theorized, the sterilized males would, under certain condi tions, compete with the normal wild males so successfully that, after repeated releases, only infertile eggs would be produced and the population would die out.
The proposal was met with bureaucratic inertia and with skepticism from scientists, but the idea persisted in Dr. Knipling’s mind. One major problem remained to be solved before it could be put to the test a practical method of insect sterilization had to be found. Academically, the fact that insects could be steril ized by exposure to Xray had been known since igi6, when an entomologist by the name of G. A. Runner reported such sterilization of cigarette beetles. 14ermann Muller’s pioneering work on the production of mutations by Xray opened up vast new areas of thought in the late 192o’s, and by the mi dle of the century various workers had reported the sterilization by Xrays or gamma rays of at least a dozen species of insects.
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But these were laboratory experiments, still a long way from practical application. About1950, Dr. Knipling launched a serious effort to turn insect sterilization into a weapon that would wipe out a major insect enemy of livestock in the South, the screwworm fly. The females of this species lay their eggs in any open wound of a warmblooded animal. The hatching larvae are parasitic, feeding on the flesh of the host. A full grown steer may succumb to a heavy infestation in I o days, and livestock losses in the United States have been estimated at $40,000,000 a year. The toll of wildlife is harder to measure, but it must be great. Scarcity of deer in some areas of Texas is at tributed to the screwworm. This is a tropical or subtropical insect, inhabiting South and Central America and Mexico, and in the United States normally restricted to the Southwest. About 1933, however, it was accidentally introduced into Florida, where the climate allowed it to survive over winter and to estab lish populations. It even pushed into southern Alabama and Georgia, and soon the livestock industry of the southeastern states was faced with annual losses running to $2o,ooo,ooo.
A vast amount of information on the biology of the screw worm had been accumulated over the years by Agriculture De partment scientists in Texas. By T954, after some preliminary field trials on Florida islands, Dr. Knipling was ready for a full scale test of his theory. For this, by arrangement with the Dutch Government, he went to the island of Cura@ao in the Caribbean, cut off from the mainland by at least 5o miles of sea.
Beginning in August 1954, screwworms reared and sterilized in an Agriculture Department laboratory in Florida were flown to Curacao and released from airplanes at the rate of about 400 per square mile per week. Almost at once the number of egg masses deposited on experimental goats began to decrease, as did their fertility. Only seven weeks after the releases were started, all eggs were infertile. Soon it was impossible to find a single egg mass, sterile or otherwise. The screwworm had indeed been eradicated on Curacao.
The resounding success of the Curacao experiment whetted the appetites of Florida livestock raisers for a similar feat that would relieve them of the scourge of screwworms. Although the difficulties here were relatively enormousan area 300 times as large as the small Caribbean island in 1957 the United States Department of Agriculture and the State of Florida joined in providing funds for an eradication egort. The project in volved the weekly production of about 50 million screwworms at a specially constructed “fly factory,” the use of 7o light air planes to fly prearranged flight patterns, five to six hours daily, each plane carrying a thousand paper cartons, each carton con taining 200 to 400 irradiated flies.
The cold winter of 195758, when freezing temperatures gripped northern Florida, gave an unexpected opportunity to start the program while the screwworm populations were re duced and confined to a small area. By the time the program was considered complete at the end of 17 months, 3% billion artificially reared, sterilized flies had been released over Florida and sections of Georgia and Alabama. The lastknown animal wound infestation that could be attributed to screwworms occurred in February 1959. In the next few weeks several adults were taken in traps. Thereafter no trace of the screwworm could be discovered. Its extinction in the Southeast had been accomplisheda triumphant demonstration of the worth of scientific creativity, aided by thorough basic research, persistence, and determination.
Now a quarantine barrier in Mississippi seeks to prevent the reentrance of the screwworm from the Southwest, where it is firmly entrenched. Eradication there would be a formidable undertaking, considering the vast areas involved and the prob ability of reinvasion from Mexico. Nevertheless, the stakes are high and the thinking in the Department seems to be that some sort of program, designed at least to Kold the screwworm populations at very low levels, may soon be attempted in Texas and other infested areas of the Southwest.
The brilliant success of the screwworm campaign has stimu lated tremendous interest in applying the same methods to other insects. Not all, of course, are suitable subjects for this tech nique, much depending on details of the life history, popula tion density, and reactions to radiation.
Experiments have been undertaken by the British in the hope that the method could be used against the tsetse fly in Rhodesia. This insect infests about a third of Africa, posing a menace to human health and preventing the keeping of livestock in an area Of some 4y2 million square miles of wooded grasslands. The habits of the tsetse differ considerably from those of the screw worm fly, and although it can be sterilized by radiation some technical difficulties remain to be worked out before the method can be applied.
The British have already tested a large number of other species for susceptibility to radiation. United States scientists have had some encouraging early results with the melon fly and the ori ental and Mediterranean fruit flies in laboratory tests in Hawaii and field tests on the remote island of Rota. The corn borer and the sugarcane borer are also being tested. There are pos sibilities, too, that insects of medical importance might be con trolled by sterilization. A Chilean scientist has pointed out that malariacarrying mosquitoes persist in his country in spite of insecticide treatment; the release of sterile males might then pro vide the final blow needed to eliminate this population.
The obvious difficulties of sterilizing by radiation have led to search for an easier method of accomplishing similar results, and there is now a strongly running tide of interest in chemical sterilants.
Scientists at the Department of Agriculture laboratory in Orlando, Florida, are now sterilizing the housefly in laboratory experiments and even in some field trials, using chemicals in corporated in suitable foods. In a test on an island in the Florida Keys in 1961, a population of flies was nearly wiped out within a period of only five weeks. Repopulation of course followed from nearby islands, but as a pilot project the test was successful. The Department’s excitement about ‘the promise of this method is easily understood. In the first place, as we have seen, the housefly has now become virtually uncontrollable by insect cides. A completely new method of control is undoubtedly needed. One of the problems of sterilization by radiation is that this requires not only artificial rearing but the release of sterile males in larger number than are present in the wild population. This could be done with the screwworm, which is actually not an abundant insect. With the housefly, however, more than doubling the population through releases could be highly objectionable, even though the increase would be only temporary. A chemical sterilant, on the other hand, could be combined with a bait substance and introduced into the natural environment of the fly; insects feeding on it would become sterile and in the course of time the sterile flies would predominate and the insects would breed themselves out of exis tence.
The testing of chemicals for a sterilizing effect is much more difficult than the testing of chemical poisons. It takes 3o days to evaluate one chemicalalthough, of course, a number of tests can be run concurrently. Yet between April i958 and December ig6i several hundred chemicals were screened at the Orlando laboratory for a possible sterilizing effect. The Depart ment of Agriculture seems happy to have found among these even a handful of chemicals that show promise.
Now other laboratories of the Department are taking up the problem, testing chemicals against stable flies, mosquitoes, boll weevils, and an assortment of fruit flies. All this is presently experimental but in the few years since work began on chemo sterilants the project has grown enormously. In theory it has many attractive features. Dr. Kniplitig has pointed out that ef fective chemical insect sterilization “might easily outdo some of the best of known insecticides.” Take an imaginary situation in which a population of a million insects is multiplying five times in each generation. An insecticide might kill go per cent of each generation, leaving 125,ooo insects alive after the third generation. In contrast, a chemical that would produce go per cent sterility would leave only 125 insects alive.
On the other side of the coin is the fact that some extremely potent chemicals are involved. It is fortunate that at least during these early stages most of the men working with chemosterilants seem mindful of the need to find safe chemicals and safe methods of application. Nonetheless, suggestions are heard here and there that these sterilizing chemicals might be applied as aerial sprays for example, to coat the foliage chewed by gypsy moth larvae. To attempt any such procedure without thorough advance re search on the hazards involved would be the height of irresponsibility. If the potential hazards of the chemosterilants are not constantly borne in mind we could easily find ourselves in even worse trouble than that now created by the insecticides.
The sterilants currently being tested fall generally into two groups, both of which are extremely interesting in their mode of action. The first are intimately related to the life processes, or metabolism, of the cell; i.e., they so closely resemble a sub stance the cell or tissue needs that the organism “mistakes” them for the true metabolite and tries to incorporate them in its normal building processes. But the fit is wrong in some detail and the process comes to a halt. Such chemicals are called anti metabolites.
The second group consists of chemicals that act on the chromosomes, probably affecting the gene chemicals and caus ing the chromosomes to break up. The chemosterilants of this group are.alkylating agents, which are extremely reactive chemicals, capable of intense cell destruction, damage to chromosomes, and production of mutations. It Is the view of Dr. Peter Alexander of the Chester Beatty Research Institute in London that “any alkylating agent which is effective in sterilizing insects would also be a powerful mutagen and carcinogen.” Dr.. Alexander feels that any conceivable use of such chemicals in insect control would be “open to the most severe objections.” It is to be hoped, therefore, that the present experiments will lead not to actual use of these particular chemicals but to the discovery of others that will be safe and also highly specific in their action on the target insect.
Some of the most interesting of the recent work is concerned with still other ways of forging weapons from the insect’s own life processes. Insects produce a variety of venoms, attractants, repellents. What is the chemical nature of these secretions? Could we make use of them as, perhaps, very selective insecticides? Scientists at Cornell University and elsewhere are trying to find answers to some of these questions, studying the defense mechanisms by which many insects protect themselves from attack by predators, working out the chemical structure of insect secretions. Other scientists are working on the socalled “juve nile hormone,” a powerful substance which prevents metamor phosis of the larval insect until the proper stage of growth has been reached.
Perhaps the most immediately useful result of this exploration of insect secretion is the development of lures, or attractants. Here again, nature has pointed the way. The gypsy moth is an especially intriguing example. The female moth is too heavy bodied to fly. She lives on or near the ground, fluttering about among low vegetation or creeping up tree trunks. The male, on the contrary, is a strong flier and is attracted even from con siderable distances by a scent released by the female from special glands. Entomologists have taken advantage of this fact for a good many years, laboriously preparing this sex attractant from the bodies of the female moths. It was then used in traps set for the males in census operations along the fringe of the insect’s range. But this was an extremely expensive procedure. Despite the much publicized infestations in the northeastern states, there were not enough gypsy moths to provide the material,’and hand collected female pupae had to be imported from Europe, some times at a cost of half a dollar per tip. It was a tremendous breakthrough, therefore, when, after years of effort, chemists of the Agriculture Department recently succeeded in isolating the attractant. Following upon this discovery was the success ful preparation of a closely related synthetic material from a constituent of castor oil; this not only deceives the male moths but is apparently fully as attractive as the natural substance. As little as one microgram (1/1,ooo,ooo gram) in a trap is an effective lure.
All this is of much more than academic interest, for the new and economical “gyplure” might be used not merely in census operations but in control work. Several of the more attractive possibilities are now being tested. In what might be termed an experiment in psychological warfare, the attractant is combined with a granular material and distributed by planes. The aim is to confuse the male moth and alter the normal behavior so that, in the welter of attractive scents, he cannot find the true scent trail leading to the female. This line of attack is being carried even further in experiments aimed at deceiving the male into attempting to mate with a spurious female. In the laboratory, male gypsy moths have attempted copulation with chips of wood, vermiculite, and other small, inanimate objects, so long as they were suitably impregnated with gyplure. Whether such diversion of the niating instinct into nonproductive channels would actually serve to reduce the population remains to be tested, but it is an interesting possibility.
The gypsy moth lure was the first insect sex attractant to be synthesized, but probably there will soon be others. A number of agricultural insects are being studied for possible attractants that man could imitate. Encouraging results have been obtained with the Hessian fly and the tobacco hornworm.
Combinations of attractants and poisons are being tried against several insect species. Government scientists have developed an attractant called methyleugenol, which males of the oriental fruit fly and the melon fly find irresistible. This has been combined with a poison in tests in the Bonin Islands 450 miles south of Japan. Small pieces of fiberboard were impregnated with the two chemicals and were distributed by air over the entire island chain to attract and kill the mate flies. This program of “male annihilation” was begun in ig6o: a year later the Agriculture Department estimated that more than 99 per cent of the popula tion had been eliminated. The method as here applied seems to have marked advantages over the conventional broadcasting of insecticides. The poison, an organic phosphorus chemical, is confined to squares of fiberboard which are unlikely to be eaten by wildlife; its residues, moreover, are quickly dissipated and so are not potential contaminants of soil or water.
But not all communication in the insect world is by scents that lure or repel. Sound also may be a warning or an attraction. The constant stream of ultrasonic sound that issues from a bat in flight (serving as a radar system to guide it through dark ness) is heard by certain moths, enabling them to avoid capture. The wing sounds of approaching parasitic flies warn the larvae of some sawflies to herd together for protection. On the other hand, the sounds made by certain woodboring insects enable their parasites to find them, and to the male mosquito the wing beat of the female is a siren song.
What use, if any, can be made of this ability of the insect to detect and react to sound? As yet in the experimental stage, but nonetheless interesting, is the initial success in attracting male mosquitoes to playback recordings of the flight sound of the female. The males were lured to a charged grid and so killed. The repellant effect of bursts of ultrasonic sound is being tested in Canada against corn borer and cutworm moths. Two authorities on animal sound, Professors Hubert and Mable Frings of the University of Hawaii, believe that a field method of influencing the behavior of insects with sound only awaits discovery of the proper key to unlock and apply the vast existing knowledge of insect sound production and reception. Repellant sounds may offer greater possibilities than attractants. The Fringses are known for their discovery that starlings scatter in alarm before a recording of the distress cry of one of their fellows; perhaps somewhere in this fact is a central truth that may be applied to insects. To practical men of industry the possibilities seem real enough so that at least one major electronic corporation is preparing to set up a laboratory to test them.
Sound is also being tested as an agent of direct destruction. Ultrasonic sound will kill all mosquito larvae in a laboratory tank; however, it kills other aquatic organisms as well. In other experiments, blowflies, mealworms, and yellow fever mosquitoes have been killed by airborne ultrasonic sound in a matter of seconds. All such experiments are first steps toward wholly new concepts of insect control which the miracles of electronics may some day make a reality.
The new biotic control of insects is not wholly a matter of electronics and gamma radiation and other products of man’s inventive mind. Some of its methods have ancient roots, based on the knowledge that, like ourselves, insects are subject to disease. Bacterial infections sweep through their populations like the plagues of old; under the onset of a virus their hordes sicken and die. The occurrence of disease in insects was known before the time of Aristotle; the maladies of the silkworm were celebrated in medieval poetry; and through study of the diseases of this same insect the first understanding of the principles of infectious disease came to Pasteur. Insects are beset not only by viruses and bacteria but also by fungi, protozoa, microscopic worms, and other beings from all that unseen’ world of minute life that, by and large, befriends mankind. For the microbes include not only disease organisms but those that destroy waste matter, make soils fertile, and enter into countless biological processes like fermentation and nitrifi cation. Why should they not also aid us in the control of insects?
One of the first to envision such use of microorganisms was the 18thcentury zoologist Elie Metchnikoff. During the concluding decades of the 18th and the first half of the 2oth centuries the idea of microbial control was slowly taking form. The first conclusive proof that an insect could be brought under control by introducing a disease into its environment came in the late I930’s With the discovery and use of milky disease for the Japanese beetle, which is caused by the spores of a bacterium belonging to the genus Bacillus. This classic example of bacterial control has a long history of use in the eastern part of the United States, as I have pointed out in Chapter 7.
High hopes now attend tests of another bacterium of this genusBacillus thuringiensisoriginally discovered in Ger many in 1911 in the province of Thuringia, where it was found to cause a fatal septicemia in the larvae of the flour moth. This bacterium actually kills by poisoning rather than by disease. Within its vegetative rods there are formed, along with spores, peculiar crystals composed of a protein substance highly toxic to certain insects, especially to the larvae of the mothlike lepi dopteras. Shortly after eating foliage coated with this toxin the larva suffers paralysis, stops feeding, and soon dies. For practical purposes, the fact that feeding is interrupted promptly is of course an enormous advantage, for crop damage stops almost as soon as the pathogen is applied. Compounds containing spores of Bacillus thuringiensis are now being manufactured by several firms in the United States under various trade names.
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The bodies of only five diseased caterpillars provide enough virus to treat an acre of alfalfa. In some Canadian forests a virus that affects pine sawflies has proved so effective in control that it has replaced insecticides.
Scientists in Czechoslovakia are experimenting with protozoa against webworms and other insect pests, and in the United States a protozoan parasite has been found to reduce the egg laying potential of the corn borer.
To some.the term microbial insecticide may conjure up pic tures of bacterial warfare that would endanger other forms of life. This is not true. In contrast to chemicals, insect patho gens are harmless to all but their intended targets. Dr. Edward Steinhaus, an outstanding authority on insect pathology, has stated emphatically that there is “no authenticated recorded in stance of a true insect pathogen having caused an infectious disease in a vertebrate animal either experimentally or in nature.” The insect pathogens are so specific that they infect only a small group of insects sometimes a single species. Biologically they do not belong to the type of organisms that cause disease in higher animals or In plants. Also, as Dr. Steinhaus points out, outbreaks of insect disease in nature always remain confined to insects, affecting neither the host plants nor animals feeding on them.
Insects have many natural enemies not only microbes of many kinds but other insects. The first suggestion that an insect might be controlled by encouraging its enemies is generally credited to Erasmus Darwin about 18oo. Probably because it was the first generally practiced method of biological control, this setting of one insect against another is widely but errone ously thought to be the only alternative to chemicals.
In the United States the true beginnings of conventional biological control date from 1888 when Albert Koebele, the first of a growing army of entomologist explorers, went to Australia to search for natural enemies of the cottony cushion scale that threatened the California citrus industry with destruction. As we have seen in Chapter i5, the mission was crowned with spectacular success, and in the century that followed the world has been combed for natural enemies to control the insects that have come uninvited to our shores. In all, about ioo species of imported predators and parasites have become established. Be sides the vedalia beetles brought in by Koebele, other importa tions have been highly successful. A wasp imported from Japan established complete control of an insect attacking eastern apple orchards. Several natural enemies of the spotted alfalfa aphid, an accidental import from the Middle East, are credited with saving the California alfalfa industry. Parasites and predators of the gypsy moth achieved good control, as did the Tiphia wasp against the Japanese beetle. Biological control of scales and mealy bugs is estimated to save California several millions of dollars a year indeed, one of the leading entomologists of that state, Dr. Paul DeBach, has estimated that for an investment of $4,000,000 in biological control work California has received a return of
$ 100,ooo,ooo.
Examples of successful biological control of serious pests by importing their natural enemies are to be found in some 40 countries distributed over much of the world. The advantages of such control over chemicals are obvious: it is relatively inex pensive, it is permanent, it leaves no poisonous residues. Yet biological control has suffered from lack of support. California is virtually alone among the states in having a formal program in biological control, and marry states have not even one ento mologist who devotes full time to it. Perhaps for want of sup port biological control through insect enemies has not always been carried out with the scientific thoroughness it requires exacting studies of its impact on the populations of insect prey have seldom been made, and releases have not always been made with the precision that might spell the difference between success and failure.
The predator and the preyed upon exist not alone, but as part of a vast web of life, all of which needs to be taken into account. Perhaps the opportunities for the more conventional types of biological control are greatest in the forests. The farm lands of modern agriculture are highly artificial, unlike anything nature ever conceived. But the forests are a different world, much closer to natural environments. Here, with a minimum of help and a maximum. of noninterference from man, Nature can have her way, setting up all that wonderful and intricate system of checks and balances that protects the forest from undue damage by insects.
In the United States our foresters seem to have thought of biological control chiefly in terms of introducing insect parasites and predators. The Canadians take a broader view, and some of the Europeans have gone farthest of all to develop the science of “forest hygiene” to an amazing extent. Birds, ants, forest spiders, and soil bacteria are as much a part of a forest as the trees, in the view of European foresters, who take care to inoc ulate a new forest with these protective factors. The encourage ment of birds is one of the first steps. In the modern era of intensive forestry the old hollow trees are gone and with them homes for woodpeckers and other treenesting birds. This lack is met by nesting boxes, which draw the birds back into the forest. Other boxes are specially designed for owls and for bats, so that these creatures may take over in the dark hours the work of insect hunting performed in daylight by the small birds.
But this is only. the beginning. Some of the most fascinating control work in European forests employs the forest red ant as an aggressive insect predator a species which, unfortu nately, does not occur in North America. About 25 years ago Professor Karl G6sswald of the University of Wiirzburg devel oped a method of cultivating this ant and establishing colonies. Under his direction more than io,ooo colonies of the red ant have been established in about go test areas in the German Federal Republic. Dr. Gosswald’s method has been adopted in Italy and other countries, where ant farms have been established to supply colonies for distribution in the forests. In the Apennines, for example, several hundred nests have been set out to protect reforested areas.
“Where you can obtain in your forest a combination of birds’ and ants’ protection together with some bats and owls, the bio logical equilibrium has already been essentially improved,” says Dr. Heinz Ruppertshofen, a forestry officer in Mblin, Germany, who believes that a single introduced predator or parasite is less effective than an array of the “natural companions” of the trees.
New ant colonies in the forests at M,511n are protected from woodpeckers by wire netting to reduce the toll. In this way the woodpeckers, which have increased by 400 per cent in io years in some of the test areas, do not seriously reduce the ant colonies, and pay handsomely for what they take by picking harmful caterpillars off the trees. Much of the work of caring for the ant colonies (and the birds’ nesting boxes as well) is assumed by a youth corps from the local school, children 10 to 14 years old. The costs are exceedingly low; the benefits amount to permanent protection of the forests.
Another extremely interesting feature of Dr. Ruppertshofen’s work is his use of spiders, in which he appears to be a pioneer. Although there is a large literature on the classification and nat ural history of spiders, it is scattered and fragmentary and deals not at all with their value as an agent of biological control. Of the 22,ooo known kinds of spiders, 76o are native to Germany (and about 2000 to the United States). Twentynine families of spiders inhabit German forests.
To a forester the most important fact about a spider is the kind of net it builds. The wheelnet spiders are most important, for the webs of some of them are so narrowmeshed that they can catch all flying insects. A large web (up to i6 inches in di ameter) of the cross spider bears some 12o,ooo adhesive nodules on its strands. A single spider may destroy in her life of i 8 months an average of 7ooo insects. A biologically sound, forest has 50 to 150 spiders to the square meter (a little more than a square yard). Where there are fewer, the deficiency may be remedied by collecting and distributing the baglike cocoons con taining the eggs. “Three cocoons of the wasp spider [which occurs also in America] yield a thousand spiders, which can catch 2,oo,ooo flying insects,” says Dr. Ruppertshofen. The tiny and delicate young of the wheelnet spiders that emerge in the spring are especially important, he says, “as they spin in a team work a net umbrella above the top shoots of the trees and. thus protect the young shoots against the flying insects.” As the spiders molt and grow, the net is enlarged.
Canadian biologists have pursued rather similar lines of in vestigation, although with differences dictated by the fact that North American forests are largely natural rather than planted, and that the species available as aids in maintaining a healthy forest are somewhat different. The emphasis in Canada is on small mammals, which are amazingly effective in the control of certain insects, especially those that live within the spongy soil of the forest floor. Among such insects are the sawflies, socalled because the female has a sawshaped ovipositor with which she slits open the needles of evergreen trees in order to deposit her eggs. The larvae eventually drop to the ground and form cocoons in the peat of tamarack bogs or the duff under spruce or pines. But beneath the forest floor is a world honeycombed with the tunnels and runways of small mammals whitefooted mice, voles, and shrews of various species. Of all these small burrowers, the voracious shrews find and consume the largest number of sawfly cocoons. They feed by placing a forefoot on the cocoon and biting off the end, showing an extraordinary ability to discriminate between sound and empty cocoons. And for their insatiable appetite the shrews have no rivals. Whereas a vole can consume about 2oo cocoons a day, a shrew, depending on the species, may devour up to 8oo! This may result, according to laboratory tests, in destruction of 75 to 98 per cent of the cocoons present.
It is not surprising that the island of Newfoundland, which has no native shrews but is beset with sawflies, so eagerly de sired some of these small, efficient mammals that in 1958 the introduction of the masked shrewthe most efficient sawfly predator was attempted. Canadian officials report in 1962 that the attempt has been successful. The shrews are multiplying and are spreading out over the island, some marked individuals having been recovered as much as ten miles from the point of release.
There is, then, a whole battery of armaments available to the forester who is willing to look for permanent solutions that preserve and strengthen the natural relations in the forest. Chem ical pest control in the forest is at best a stopgap measure bring ing no real solution, at worst killing the fishes in the forest streams, bringing on plagues of insects, and destroying the natural controls and those we may be trying to introduce. By such violent measures, says Dr. Ruppertshofen, “the partnership for life of the forest is entirely being unbalanced, and the catastrophes caused by parasites repeat in shorter and shorter periods … We, therefore, have to put an end to these unnatural manipulations brought into the most important and almost last natural living space which has been left for us.”
Through all these new, imaginative, and creative approaches to the problem of sharing our earth with other creatures there runs a constant theme, the awareness that we are dealing with life with living populations and all their pressures and counter pressures, their surges and recessions. Only by taking account of such life forces and by cautiously seeking to guide them into channels favorable to ourselves can we hope to achieve a reason able accommodation between the insect hordes and ourselves.
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The current vogue for poisons has failed utterly to take into account these most fundamental considerations. As crude a weapon as the cave man’s club, the chemical barrage has been hurled against the fabric of life a fabric on the one hand deli cate and destructible, on the other miraculously tough and resilient, and capable of striking back in unexpected ways. These extraordinary capacities of life have been ignored by the prac titioners of chemical control who have brought to their task no “highminded orientation,” no humility before the vast forces with which they tamper.
The “control of nature” is a phrase conceived in arrogance, born of the Neanderthal age of biology and philosophy, when it was supposed that nature exists for the convenience of man. The concepts and practices of applied entomology for the most part date from that Stone Age of science. It is our alarming mis fortune that so primitive a science has armed itself with the most modern and terrible weapons, and that in turning them against the insects it has also turned them against the earth.
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