These Male Spiders Acrobatically Catapult to Avoid Sexual Cannibalism

Male orb-weaving spiders don’t stick around long after mating. 

New research finds they acrobatically fling themselves away from their partners immediately after sex. It’s not because they hate snuggle time. It’s because they know if they stay, they’ll be eaten.

“We found that mating was always ended by a catapulting, which is so fast that common cameras could not record the details clearly,” says lead author Shichang Zhang of Hubei University in Wuhan, China, in a statement.

Researchers studied orb weavers (Philoponella prominens) immediately after mating. They found the males used a joint in their first set of legs to immediately catapult away from their partners at speeds as fast as 88 centimeters per second.

They observed 155 successful matings. Among those, 152 (97.4%) males catapulted away from the females and they all survived. However, the three males that didn’t fling themselves away after mating were killed and eaten by their partners.

The researchers then put a fine brush behind the upper back (dorsum) of 30 male spiders to block them from jumping after mating. All of those spiders were also captured and consumed by the females.

Using high-resolution video images, they calculated the speeds and accelerations of the males as they catapulted. Their speed ranged from 31.6 to 88.2 centimeters per second. Acceleration ranged from 74.2 to 528.7 meters per second squared. When they soar through the air while catapulting, they spin an average of about 174 times per second.

The findings were published in the journal Current Biology

Hydraulics and Jumping

Orb-weaving spiders are a group of more than 2,840 species known for their distinctive orb-shaped webs.

The males in the study can mate with the females as many as six times. They have a silk “safety line” that allows them to fall off and then climb back to mate again. The researchers refer to it as a “bounce off, climb up with safety line, mate, and bounce off again” cycle.

In the study, they also cut the safety line in 20 males. They still catapulted after mating but just dropped to the ground.

Researchers found the males folded their tibia-metatarsus joint in their first set of legs against the female during mating. When they are released, there’s hydraulic pressure that allows the legs to rapidly expand. That particular joint doesn’t have extensor muscles in spiders so they rely on motion to push out their legs.

Male spiders with superior locomotion still might be able to perform this catapulting move many times, which allows them to mate over and over, thereby increasing their chance of fathering offspring.

“This creates the stage for antagonistic coevolution where females can afford high levels of sexual cannibalism while not jeopardizing their mating opportunities, and males evolve behaviors, such as the rapid catapult on safety lines, to counter the effects of sexual cannibalism,” the researchers write.

“We observed that males that could not perform the catapulting were cannibalized by the female. It suggests this behavior evolved to fight against female’s sexual cannibalism under strong predation pressure of females," Zhang says.

“Females may use this behavior to judge the quality of a male during mating. If a male could not perform catapulting, then kill it, and if a male could perform it multiple times, then accept its sperm.”