A. studiosus is found in both North and South America, where it builds big communal webs housing approximately 40 female spiders. Other spider species are similarly social, but A. studiosus is the only one known to have two distinct personality types—one nice and one not so nice. 

Docile spiders tend to stick closer to home when starting new colonies, and they rarely fight predators or hunt for prey. Aggressive-type spiders, on the other hand, are always looking for a fight. And when it comes time to leave the web, they venture out much further than the docile spiders. Each spider has one personality type or the other, and they pass that personality type on to their offspring. With mixed parents, baby A. studiosus spiders will still end up with one disposition or the other, not somewhere in between.

The question for biologists, then, is why would two such distinct personalities evolve and persist? To answer that, behavioral ecologist Jonathan Pruitt collected some wild female spiders in Tennessee and brought them into his lab. Here, Pruitt did some spider matchmaking. He divvied up the spiders into pairs—either two aggressive spiders, two docile spiders, or one of each.