This Male Spider Catapults Itself Into the Air to Avoid Sexual Cannibalism

A bad date can be an unmitigated disaster of awkwardness for humans, but for male spiders it often means being eaten alive by the much larger, hungry female. To avoid being cannibalized after sex, the males of some species have had their legs ripped off to distract their loved one with food or to tie up the female's legs with silk.

The males of the orb-weaving spider are opting for another strategy that might appeal to anyone who has ever wished for an exit button during a date that has gone downhill fast. According to research published today in Current Biology, males use their two front legs to catapult themselves to safety as soon as they have sex.

The males that don't launch themselves out of their lover's embrace in time suffer a terrible fate. The hackled orb weavers are a family known for their work. These spiders don't have venom that can help them kill. The less spry spider-men are mummified so tightly that their legs break that they are either crushed to death or suffocate. 450 feet of silk was found in a 2006 study of another spider in this family.

Shichang Zhang, an arachnologist at Hubei University and lead author of the study, wrote in an email that he and his colleagues were studying the sexual behavior of this species, which lives in communal webs of up to 300 individuals, when they noticed tiny males.

Why the males were jumping off the females, which body parts the males were using to do it, and what kind of speed and acceleration they managed to achieve were three concepts that Zhang wanted to understand. He brought high-speed cameras and a lot of spiders to the lab to do this.

The team observed 155 instances of successful spider mating, and all but three of the males involved flung themselves as far away from the female as they could. The three males that stuck around were killed and eaten by their sexual partners.

The researchers blocked the ability of 30 male spiders to launch themselves in order to see what would happen if the males couldn't jump away. The idea that this behavior on the part of males helps them survive is supported by the fact that all 30 males were eaten.

To get a better idea of the mechanics of how these males were flinging themselves, the spiders were filmed with cameras capable of filming at 1,500 frames per second. It takes about 30 seconds for a spider to mate, and filming such small creatures during such a fleeting act proved difficult.

The spider is small, so most of the time, males had catapulted before the focus was ready.

The high-speed, high-resolution videos eventually revealed that the male spiders appeared to be catapulting themselves by folding their two front legs against the female's body at the spider-equivalent of the knee joint, and then suddenly extending the legs when it was time to leave. The movement is similar to a competitive swimmer starting a backstroke race. The swimmer starts with their legs folded and braced against the pool wall and then they explode backwards when the race starts.

The spiders reached speeds of up to 1.9 feet per second and a peak speed of 1734.5 feet per second squared, according to the analysis of the high-speed videos. The spiders would hit 60 miles per hour in about 0.05 seconds if they sustained that level of acceleration for longer than the average four millisecond duration recorded by the researchers. The male spiders spun a lot while flying through the air, but it's not clear what function, if any, that might serve.

The researchers wanted to know if the male spiders were using their front legs to retreat. One or both of the two front legs were removed in one test. The 60 males involved in the experiment were unable to have sex because of the loss of one or both foreleg. The suitors courted females, but didn't try to get them to marry them.

In a second test, researchers removed one or two of the spider's other six legs, which had no apparent ill effects on mating success or their ability to catapult away.

The researchers made a small hole in the back of the spider with a needle. The researchers did this because spiders don't have the muscles to extend their legs. These eight-legged lover boys rely on pressure to extend their legs and jump into the air.

Spiders have a big muscle in their thorax that they can use to shoot their body fluid into their legs and cause them to move quickly.

When the researchers pierced the legs of the spiders, it was likely impossible for them to create enough pressure to extend the leg. The males that got this treatment kept their distance, instead of trying to get intimate with the females.

The males of jumping spiders use their first pair of legs to shoot themselves into the air, which is odd since the back four legs are used to jump.

The biophysicist at Georgia Tech, who was not involved in the research, says he finds it fascinating that they can do this without muscles.

The study suggests that this behavior on the part of males evolved as an adaptation to the female spider's proclivities for sexual cannibalism. He says that one male was able to perform the behavior six times over the course of about eight hours, but was killed and eaten after his final performance--perhaps being too exhausted to save himself. According to the paper, the bounciest males might father more spiderlings by having sex with the same female multiple times without being eaten, or by seeking out additional mates.

Bhamla says that the study made him smile and remember that spiders are cool.