Male wasps use their genital spines to sting frogs (and people)

Until recently, female wasps got all the blame for those painful pricks.
A yellow and black wasp lands on a green leaf.
It turns out, not only female wasps sting. Deposit Photos

Sometimes science bites—stings even. Researcher Misaki Tsujii from Kobe University in Japan found this out firsthand while studying the life history of the mason wasp (Anterhynchium gibbifrons) when she got stung. While stings are part of the risk when studying bees, something unexpected happened.

“Surprisingly, the male ‘sting’ caused a pricking pain,” said Tsujii’s research partner Shinji Sugiura, also from Kobe University. With wasps, it’s usually the females that sting predators. “Based on her experience and observations, I hypothesized that the male genitalia of A. gibbifrons function as an anti-predator defense,” Sugiura said.

[Related: Bees can sense a flower’s electric field—unless fertilizer messes with the buzz.]

It’s already known that female bees and wasps use modified ovipositors—a body part also used in egg-laying—to sting their attackers, including humans. These venomous stings are used to defend themselves and their colonies, but since the females have evolved venomous stings from ovipositors, scientists believed that these male bees weren’t as dangerous. A study published Monday in the journal Current Biology details how male mason wasps use their sharp genital spines to attack and sting predatory tree frogs to avoid being swallowed.

“The genitalia of male animals have frequently been studied in terms of conspecific interactions between males and females but rarely in terms of prey-predator interactions,” said Sugiura, in a statment. “This study highlights the significance of male genitalia as an anti-predator defense and opens a new perspective for understanding the ecological role of male genitalia in animals.”

To learn more, they placed male wasps with tree frogs (Dryophytes japonica). All of the frogs attacked the male wasps, and just over a third of the frogs spit the wasps out.

[Related: Bees choose violence when attempting honey heists.]

“Although all of the pond frogs ate the male wasps, 35.3 percent of the tree frogs ultimately rejected them,” they write in the study. “Male wasps were frequently observed to pierce the mouth or other parts of frogs with their genitalia while being attacked.”

A tree frog spitting out a male wasp after being hit with pseudo-stings. CREDIT: Current Biology, Sugiura.

They then gave tree frogs wasps that didn’t have their genitalia, and the frogs promptly ate them. Since frogs ate all of these genital-less male wasps, the results of the experiment appear to show the male wasps used their genitalia as a stinging mechanism to prevent the frogs from swallowing them.

The paper says that this is evidence that, just like their female counterparts, males use their genitalia to avoid being eaten by stinging their predators. These genital spines, called “pseudo-stings,” are found in some other wasp families (including Tiphiidae and Sphecidae, among others), so the team believes this newly discovered defensive role is likely found in multiple other wasp species in addition to the mason wasp.