Silent Spring: Chapter 15,16

Summary of Chapter 15: Nature Fights BackCarson notes the irony that despite the cost of our war on insects, we have failed. They are fighting back and adapting to our poisons. Chemicals fail, she asserts, because they cannot take into account the complex and precise systems of nature. The only effective control on insects has been devised by nature itself, not by humans. Insects war among themselves.  Ecologists call this the resistance of the environment, meaning the limited amount of food and natural predators present at a given time. When the resistance of the environment is broken down by human interference, the ability of a species to reproduce is “truly explosive” (p. 218). Nature has its own mysterious system of checks and balances. When humans with limited awareness interfere, then they get a scenario like trying to eliminate the coyote, only to get plagues of field mice. Similarly, she points out, 70 to 80 % of the earth’s creatures are insects, and no amount of chemicals can keep them in balance, only other predators: “nature controls her own” (p. 220). Carson gives examples of a number of insects and their natural checks through other insects such as ladybugs, dragonflies, wasps, and lacewings. Insecticides, on the other hand, lower the environmental resistance, year by year, allowing more disease-carrying insects to thrive. Spider mites, for instance, thrive on insecticides, thus allowed to kill whole forests. Their natural checks, such as ladybugs, have been eliminated by blanket spraying.
Commentary on Chapter 15: Nature Fights BackCarson quotes one expert who says that once we set our foot on the chemical treadmill, we cannot stop, because the ensuing imbalance has to keep being addressed. But disease follows in the wake of the poisons, as for example, when pesticides kill fish. Snails eat the contaminated carcasses and increase in number. They are hosts to dangerous blood flukes that go into the water and cause human and animal disease. Carson laments that most entomologists are not now looking into natural controls but researching insecticides because chemical companies are funding universities. To balance this picture she gives the example of Dr. Pickett of Nova Scotia who spent his life researching natural insect controls for apple orchards with great success.
Summary of Chapter 16: The Rumblings of an AvalancheDarwin would be delighted to find the insect population proves his theory of survival of the fittest. Chemical spraying kills off the weaker insects and allows the stronger ones to survive who are more and more resistant to sprays. It was DDT, Carson says, that ushered in “The Age of Resistance” (p. 233) as the genetics of insects even far from spraying sites registered the information that insecticides were not lethal to them. Resistance is developing so fast it has become a health crisis, in terms of mosquitoes, ticks, lice, cockroaches, and other vectors of disease. One method of dealing with the problem is to keep switching insecticides, but that has a limited success. Chemical companies keep inventing new chemicals, but the cost of chemical control is rising, and materials cannot be stockpiled, for they are soon outdated.
Commentary on Chapter 16: The Rumblings of an AvalancheThe question is asked, if insects become resistant to chemicals, can humans? Carson says that true resistance is something that develops in a whole population over many generations. Insect generations are short, and human cycles are longer. The advice of some experts, therefore, is to spray as little as possible.