The ever-shifting balance of nature is threatened by modern insect control programs, which cannot foresee their complex effects on a living community of interdependent creatures. In fact, the ‘resistance of the environment,’ of natural predators and prey operating in a system of checks and balances, is the only really effective, natural measure for fighting infestation, and this natural resistance is only weakened by indiscriminate spraying. And so the final irony is that, even as we have risked so much in an attempt to control nature, our efforts have inevitably failed.
When birds and other predators are destroyed by pesticides, the natural system of checks and balances is disrupted in ways that isolated testing failed to predict, so that pest populations boom. Although we have the power to change our environment, we are not doing so in a way that humbly admits the enormous quantity of information we still do not know about the complexities of ecology.
Natural population dynamics are complex and carefully calibrated. When natural predators of Kaibab deer in Arizona were killed off in a conservation effort, the population of deer ballooned and then collapsed from lack of food. Insects, too, have this system of predator/prey checks and balances which results in a careful balance. Carson lists a number of examples, from dragonflies to ladybugs to wasps, whose incidental destruction from broad, blanket spraying actually ended up leading to a ballooning of the originally targeted pest population.
This is a perfect example of these complexities, and of the ways that man’s attempts to intervene, to re-engineer a pre-existing system, can easily backfire in unexpected ways. What we can expect is that intervention, without proper research, and especially in the unintelligent, indiscriminate form of blanket spraying, will change the natural balance in some way, and perhaps dangerous ways.
This phenomenon explains why after sprayings pests have been seen to rebound massively, as Carson proves with accounts from all over the world. Blackflies in Ontario became 17 times more abundant after spraying was completed. The spider mite has become a worldwide pest since DDT has killed off its natural enemies, attacking evergreen trees with its voracious appetite for chlorophyll, which makes leaves green. This happened in 1956 when western national forests were sprayed with DDT after a budworm infestation, and the following summer brought a blight of brown trees.
The record of man’s attempted interventions seems to prove they are foolish. Over and over again, the interconnected, complex ecology into which pesticides enters is changed in such a way that the targeted pests are actually allowed to thrive! By spreading this message to the public, Carson is clearly aiming to motivate a change in the everyday citizen’s understanding of pesticides and their effectiveness, weighed against the dangers they pose.
Conversely, imported natural predators have shown good results in reducing populations – until they themselves are eliminated by pesticides. In California, great success with an inexpensive biological control involving a parasite of the destructive scale insect was reversed when spraying killed off the parasite, a small ladybug called the vedalia. New methods are more expensive and destructive, and less coordinated.
Following nature’s example by taking advantage of the web of checks and balances, importing predators and parasites to deal with ballooning pest populations, is a much more sustainable and effective option. This is what the new era of man should look like.
This effect is still more sinister when considered in the context of disease-carrying insects. Mosquitoes that carry malaria flourish from a lack of predators after chemicals are applied, unless pesticides are re-applied year after year. Snails, which can transmit parasitic worms, seem to be immune to pesticides, and their numbers increase when their natural predators are killed off by sprayings.
Another unintended consequence of intervention into the interconnected system of nature is the spread of disease, when pests that carry pathogens are allowed to multiply without their natural predators. We must protect ourselves from this danger by exercising caution.
Despite the seeming folly of pesticides and the promise of biological solutions, research into chemical options for control of “pests” far exceeds that for biological ones. One reason is that insecticide companies endow fellowships and research, but no corollary exists for biological control. Dr. A.D. Pickett is one exception, pioneering natural methods and minimizing the damage of specifically applied, gentler pesticides. He denounces indiscriminate spraying, describing it as a route to crisis after crisis.
To break out of the pattern of crises that justifies spending on pesticides, we must invest in biological solutions, which Carson has shown are more compatible with ecological communities. Unless we as a species want to live on the edge of survival – struggling just to survive – these biological controls must be publicly supported as a replacement for pesticides.