Male wasps are actually considered harmless because they lack the notorious sting of the females. But now researchers are reporting on a species in which the males have upgraded in a bizarre way: their penis has side "daggers" with which they can effectively defend themselves against enemies such as frogs. Even humans can feel the genital weapon. The scientists say that the masculine defense concept has probably also remained undiscovered in other representatives of the solitary wasps. It is, they say, a whimsical example of evolutionary “ingenuity”.
From horns to spikes: Nature has developed a whole range of concepts that animals use to keep their enemies at bay. In some species, certain parts of the body have been turned into weapons. The poisonous stinger is notorious among insects: Bees and wasps in particular are known for being able to let these structures shoot out of their abdomen in order to ram them into the body of attackers. So far, however, it has been assumed that only the female bees and wasps can defend themselves in this way. This is because the poisonous sting developed from the female egg-laying burr, which males do not have.
A surprising pain
At the beginning of the study by the entomologists Shinji Sugiura and Misaki Tsujii from the Japanese University of Kobe there was a surprising sting. Tsujii was examining a supposedly harmless male of the solitary wasp Anterhynchium gibbifrons when she suddenly had an unpleasant experience: the insect gave her a stinging pain on her finger. Subsequent investigations then made it clear that this was caused by two sharp objects that the animal can shoot out of its abdomen. In contrast to the female sting, however, the males do not transfer any poison with this sting, the researchers found.
As they explain, the sharp structures are parts of the males' genital apparatus: the two extensions lie laterally around the actual penis of the insect. In principle, such structures were already known, but it was previously assumed that they only have a function during pairing. However, as further investigations have shown, this is not the case with Anterhynchium gibbifrons: the processes are therefore not used at all during copulation. So it was obvious that the males use the dagger-like genital spikes instead to defend themselves against attackers. Sugiura and Tsujii were finally able to prove this function experimentally.
Roughly escaped from the frog's mouth
They put male A. gibbifrons wasps in front of the Japanese relatives of our tree frogs. The amphibians gladly accepted the prey - but as it turned out, in many cases they spit the wasps out again after the attack. The reason became clear in the film recordings: the male wasps rammed their genital stingers into the tongue or mouth of the attackers. However, when the scientists used tweezers to deprive the insects of their weapon, they all ended up in the frogs' stomachs. So, much like the females use their venomous spines, A. gibbifrons males use their genitals for defense. It is the first evidence of the use of a genital apparatus for this purpose, the researchers say.
“The genitals of male animals have usually only been studied with regard to the interaction between males and females. This study now shows that they can even be of importance for the defense against predators, and thus opens up new perspectives," says Sugiura. Because the two scientists suspect that the concept is not limited to Anterhynchium gibbifrons: Similar projections on the genitals are also known from other wasp species. They may also be used for defense, say Sugiura and Tsujii.
Source: University of Kobe, professional article: Current Biology, doi: 10.1016/j.cub.2022.11.030
Photo & video credit: Shinji Sugiura