Daddy long legs perform fellatio—and other wild facts about how these arachnids mate

You probably haven’t thought much about the sex lives of arachnids—if at all—but it turns out some daddy longlegs have surprisingly complex, lurid and even violent mating habits. Research has shown, for example, that a species of female harvestmen (as daddy longlegs are also called) will perform fellatio to avoid potential violence from males. In another species, meanwhile, males secrete an apparently extremely tasty substance on their penis that entices female mates.

“We already knew that some animals perform fellatio, like bats and bonobos. What we didn’t know—and haven’t seen in previous studies—is that females might use it to get out of engaging in intercourse,” says Pavol Prokop of Comenius University Bratislava in Slovakia, a member of the team that made the discoveries. “These harvestmen have showed us that anything is possible! It’s a really exciting discovery.”

In general, harvestman sex works like this: Males initiate mating by using their pedipalps—leglike appendages near the mouth—to grab females’ second pair of legs. Typically they’ll rub their penis against the female’s mouth. Then they insert the penis into the female’s genital opening just underneath.

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A group of researchers in Slovakia was studying other aspects of harvestman mating when they noticed males being particularly aggressive, so they decided to investigate. They scooped up 230 young Phalangium opilio harvestmen (also found in much of North America) and fed them crickets, fish flakes and apples until they were sexually mature. Then they put the females together with one male, then another.

The females didn’t seem too interested. They showed at least some resistance 91 percent of the time—especially when encountering the second male, Prokop says. But what came next really triggered a double take: males showed significant aggression towards reticent females, biting their legs and bodies, sometimes leading to fractures and death—four females were cannibalized. That’s in stark contrast to their arachnid cousins, spiders, whose females that tend to be violent, attacking and eating the males. “We were extremely surprised,” Prokop says. “It was a completely different story compared to what’s been previously told about arachnids.”

Perhaps in an effort to minimize their sexual encounters, about 44 percent of the females licked the males’ penises, Prokop says, which shortened the duration of copulation—some females even avoided mating altogether.

The team recently investigated the mating habits of another species, Leiobunum limbatum, which showed quite a different routine. Males of this and some other harvestmen species have a sac on their penis filled with a nonsperm liquid, and in trials with 130 harvestmen, the researchers found that females were much more willing to mate; they did so several times with both the first and second visitors and “routinely” licked the sac to lap up liquid, Prokop says. He adds that when the males were rejected, they simply walked away without any sign of aggression.

The violence of the first species, Phalangium opilio, came as a surprise to Anita Aisenberg, an evolutionary biologist at the Clemente Estable Biological Research Institute in Uruguay, who wasn’t involved in either study. She says males wouldn’t benefit from damaging females that might become the mother of their offspring but suggests it’s possibly “spillover” aggression from males’ propensity to fight each other.

Prokop says he has seen such intense male-to-male aggression in his laboratory, but he says it also makes sense that males might simply prefer to make a meal out of a female that consistently refuses to reproduce with them. “It’s a very pragmatic decision,” he says.

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