Sunday I declared war on a pair of yellow jacket nests at the base of my house, and it got me thinking. According to conventional wisdom, when I use an anti-yellow jacket spray, I impose a negative externality on other people, because I make the yellow jacket population more resistant to the spray. In Darwinian terms, the yellow jackets that are less vulnerable are more likely to survive, leading the next generation to be less vulnerable.

This is a common counter-argument to those who allege that anti-DDT regulation led to millions of deaths from malaria: You can’t do a linear extrapolation, because the mosquitos would have built up resistance anyway. (See also here).

But on reflection, matters are more complex. One way the yellow jacket population might adapt to spraying is to build up resistance. But there is another adaptation that seems at least as likely: Learning to fear human beings and avoid nesting near human settlements.

Think about deer. People have been hunting them for ages. And they have built up very little resistance to bullets. In part, this is because our technology advances faster than they can adapt. But the main reason is that deer have largely adapted in a different direction: Running like deer at the first sight of us.

The interesting thing about the adaptation of “fearing humans” is that it is actually a positive externality of my spraying. When I kill yellow jackets who get too close to my house, it also makes yellow jackets less likely to nest near my neighbors’ houses.

You might think that the adaptation route would depend on animal species’ generational cycle. The shorter-lived the animal, the more rapidly they adapt. (Think of bacteria). But it’s not clear why this would make one kind of adaptation more likely than the other. (Of course, if animals actually learn, rather than simply making the evolutionary cut, then it’s a different story. An animal can learn to fear man, but not to survive toxic sprays).

The net effect of these negative and positive externalities? It could go either way, and presumably varies from case to case. Until I’ve got good evidence one way or the other, my motto shall remain: Spray and let spray.