Summer World_ A Season of Bounty - Bernd Heinrich [94]
There is an incredible toughness to life, but at the same time a frailty that borders on the absurd. We supplement our milk with vitamin D, which we need for our health, but vitamin D is also used as a rodenticide. A polar bear has a huge amount of vitamin A in its liver, enough to kill a human who eats it. I think I have been especially sensitive to frailty versus toughness because of my experience in trying to keep wild animals as pets or to domesticate wild plants—to say nothing about trying to get them to reproduce. Almost invariably, for any one species there is a huge list of what seem like absurdly fussy requirements related to its natural environment, requirements that are often almost impossible to consciously duplicate.
One chemical, which seemed so nontoxic that people offered to ingest it, turned out to be deadly. This was dichlorodiphenyltrichloroethane, more commonly referred to as DDT, an insect poison that broke down to dichlorodiphenyldichloroethylene (DDE), the active culprit that affected birds. It took years for the effects of this toxin to be identified. The offending chemical first had to be passed on from one organism to another; in some of these organisms it did no discernible harm, but eventually it reached some which it did harm. It was slow-acting and did not directly affect the birds’ mortality. It affected their behavior, and the thickness of their eggshells—especially in pelicans, who ate fish that fed on aquatic invertebrates; and in raptorial birds, particularly falcons, because they ate birds who had eaten insects. Thanks to the alerts sounded by naturalists, and to long, patient, expensive sleuthing, DDT was eventually identified as the source of the devastation. Heroic countermeasures were instigated, and they reversed the trend toward what would otherwise have been the obliteration of more than I dare to contemplate. The scary part is that DDT was solemnly sworn to be a safe chemical—it had been extensively tested before being released. And now, many decades later, we are still finding out more: for example, that exposure of girls to DDT prior to puberty greatly increases their risk of breast cancer later in life. We still release about fifty new chemicals into circulation per week. They are tested on lab rats—animals that never experience summer or winter, that live well in dumps, and that when tested have no relation to any ecosystem except a sterile cubic plastic box. The chemicals don’t get tested in a pristine bog where the olive-sided flycatcher sings and the bumblebees collect nectar and pollen from pink rhodora blossoms in early summer, and where blue pickerelweed flowers poke up out of the water of the languid stream flowing through it in July and August.
In the summer of 2008, I finally saw Bombus terricola again. I found one dead in Hinesburg, Vermont, and in Maine I regularly saw several live ones in three places where I looked (Hog Island, in Muscongus Bay; in western Maine on my hill, and near Orland). A continuing comeback of the species is likely. I suspect now that its severe setback for over two decades could have been due to a “wildfire” effect; a very high former population was dense enough for an emergent or new pathogen to easily spread from one bee to another. The high bee population favored the lethality of the pathogen on those bees. If this is correct, the surviving bees will now have evolved increased resistance, and the surviving pathogens will have evolved reduced virulence. A dieback by chemicals, on the other hand, would likely have affected many species simultaneously.
22
Ending Summer
CHEMICALS CAN BE POWERFUL. ONE—THE CHLOROPHYLL molecule—causes the greening in spring that is the basis of the summer world. Without chlorophyll, life as we know it would not exist on Earth. Another chemical, which trees