Spider webs present an intriguing challenge to evolutionary biologists.

These finely honed death traps come in many forms, from the trampoline-like construction of the sheet web spider, to the instantly recognizable filigree of the orb weaver. Orb-style webs are made by diverse spiders, however, and there are two different types, one that’s sticky and one that’s not. Ever since biologists began to sort out how tens of thousands of different species of spiders are related to one another, sketching a very large, many-legged family tree, they have wondered: Did spiders evolve to spin the orb web only once? Or multiple times?

It’s an important distinction, and one that scientists who study the evolution of spiders have fiercely debated.