When Steven Anderson first examined a specimen of the Iranian spider-tailed viper, he, of course, noticed the arachnid-shaped lump on the dead snake’s tail. It was 1970, and the herpetologist was at the Field Museum in Chicago examining what the museum assumed to be a Persian horned viper, a snake common throughout the Middle East.

But this one had such a bizarre growth on its tail. To Anderson, a biologist who studies reptiles in Southeast Asia, it resembled “an oval knob-like structure,