Male wasps lack a stinger, but their penises carry effective spines that they use as a weapon to avoid ending up in the bellies of their predators, a study published on Monday reveals.
Thanks to an accidental sting, Japanese scientists have discovered this defence mechanism in male wasps which, unlike females, do not possess the dreaded sting containing venom.
Despite this handicap, they manage to escape from their predators, but through behaviour that had been poorly understood until now.
The hypothesis that certain male insects can sting with their genitals had been put forward by scientists, “but proof was lacking,” explains Shinji Sugiura, of Kobe University, co-author of the study published in the journal Current Biology.
"I thought the males were harmless"
Sugiura, who specialises in anti-predator strategies in animals, was alerted when one of his students, Misaki Tsujii, a co-author of the study, was stung by a male mason wasp.
“I tried to get stung myself, and because I thought males were harmless, I was very surprised to feel the pain of a sting,” Shinji Sugiura told French news agency AFP.
He suspected the two large spines on either side of the insect’s penis caused the pain. He decided to test this hypothesis in the laboratory by offering wasps as meals to two species of tree frogs.
“We observed many males piercing the mouths or other organs of the frogs with their genitals at the time of the attack,” he says.
Predators spit out the males after being stung
One of the videos of the attacks shows an unlucky frog unsuccessfully trying to chew the insect, before using its front leg to vigorously spit out its prey. In total, more than a third of the predators ended up spitting out the males after being stung.
The experiment was replicated with wasps from which the genitals had been removed: the frogs made short work of them.
The difference between the situations was “statistically significant,” which suggests that this survival strategy in males has played a role in the evolutionary history of wasps, Shinji Sugiura stressed.
More research need on the use genitals for defence
Apart from their reproductive role, the genitals of insects are still little studied. However, previous research has shown how sphinx butterflies use their genitals to emit ultrasound against bats.
Shinji Sugiura himself has researched how some beetles manage to escape once swallowed, by exiting through the anus of their predators.
The biologist now hopes to determine whether other families of wasps have the same genital stings as a defence system.
