Male spiders avoid sexual cannibalism with a catapult mechanism

In the animal world, numerous mechanisms have been described that allow for extremely fast actions or reactions via the slow storage of energy, typically in elastic structures, which is then nearly instantly released^1-4, similar to the operation of a catapult. Many of these mechanisms are employed for prey capture^1,2 or for predator avoidance^3,4; however, such superfast actions have not yet been reported as a means to dodge sexual cannibalism. Here, we unveil a novel mechanism in a communal orb-weaving spider Philoponella prominens (Uloboridae) (Figure S1), whereby males undertake a split-second catapult action immediately after mating, thereby fleeing their partner (Video S1). We demonstrate that males achieve their superfast action (up to 88.2 cm/s) by extending the tibia-metatarsus joint of their first leg pair via hydraulic pressure in a joint that is known to lack extensor muscles in spiders. This rapid expansion greatly reduces the likelihood of the male being sexually cannibalized.