It's a familiar sight: you're driving along one of those long, dry stretches of highway in any of the southwestern states, and you keep coming across snakes that have been run over by cars.

Why should snakes have worse luck with cars than any other desert animal does?

One reason is that snakes are cold-blooded that is, their body temperature isn't maintained internally the way ours is, but fluctuates with the temperature of their environment. If you are cold-blooded and you live in the desert, you will find yourself getting very chilly at night, because sandy terrain does not hold heat very long after sunset. To get around this, snakes will often "bask" on warm rocks; they also seek hot places to help aid in their digestion.

This, in fact, is true of any snake, no matter what part of the country you find them in. The deserts just make a particularly clear case exactly because they do get cold so fast at night, and snakes can't hide out in wooded or grassy areas.

Now you can probably see the problem that comes when human beings enter into the picture. When we move into deserts, we build those long roads out of asphalt and other materials that retain heat long after the sun has gone down. Desert snakes come out to bask away the cold hours on these convenient stretches of warmth. This obviously turns out to be a mistake.