Male spiders avoid sexual cannibalism with a catapult mechanism

The animal world provides numerous examples of mechanisms that allow for extremely fast actions or reactions via slowly storing energy, typically into elastic structures, that is then nearly instantly released, similar to the operation of a catapult. While these mechanisms are usually employed for prey capture or for predator avoidance, such superfast actions have not been reported as a mechanism to dodge sexual cannibalism. Here, we unveil a novel mechanism in a communal orb-weaving spider Philoponella prominens (Uloboridae), whereby males undertake a split-second catapult action immediately after mating, thereby fleeing their partner. 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 across spiders. This rapid expansion greatly reduces the likelihood of the male being sexually cannibalized.