Male jumping spiders can’t rely on flirting alone. To win a mate, Lyssomanes viridis males (pictured above) must often do battle with one another, extending their colorful fangs, waving their forelegs in combative displays, and head-butting each other until one of them gives way. But males who fight every battle to the fullest end up exhausted or dead. So how do jumping spiders decide which other males they’re willing to fight? To find out, researchers designed their own computer-animated jumping spiders and had them confront live specimens in a lab (see video here). The animated spiders varied in body size as well as in fang and leg length; in each case, the scientists observed whether the live spiders would escalate a battle. Surprisingly, the spiders were just as willing to fight animations with long legs and fangs than those with less imposing weapons. But they consistently retreated from challenges made by animations that had significantly bigger bodies than their own, the researchers report online this month in Behavioral Ecology. That suggests that the size difference between spiders—rather than body size alone—may be the best predictor of whether two males end up in combat.
(Linked video credit: Cynthia Tedore)