Engard! Wasps use penile spines to ward off predators

An accidental sting has helped Japanese scientists prove that some male wasps have a rather unusual predatory defense weapon: penis spines.

While wasps are known for their spiky attacks, only the females have a real stinger in their tail. Their male counterparts generally elude predators by mimicking the fairer sex.

Scientists had theorized that some male wasps might have other defense mechanisms, including perhaps using their genital spines.

“However, the evidence was lacking,” explains Shinji Sugiura, an ecologist at Japan’s Kobe University.

Sugiura studies animal defenses against predators, but it was only by coincidence that he studied the male wasp’s unusual mechanism after his graduate student and co-author reported being stung by a masonry wasp.

“I tried to get stung after hearing about her experience,” Sugiura told AFP.

“Because I thought male wasps were harmless, I was very surprised to feel the pain.”

Female wasps sting via an ovipositor, a tube-like protrusion that deposits eggs but can also provide a venomous response.

Male wasps lack the organ but are equipped with two large stingers that sit on either side of their penis.

To test the effectiveness of this defense, Sugiura’s team offered male mason wasps two different types of frogs to see how the stingers were deployed.

“Male wasps have frequently been observed to pierce the mouth or other parts of frogs with their genitals while they were being attacked,” Sugiura reported in a study published Tuesday Current Biology Diary.

The attacks are documented in video showing an unfortunate frog repeatedly attempting to bite a wasp before pulling the stinging insect out of its mouth with its forefeet.

Pond frogs happily ate all males as well as stinging females, but over a third of tree frogs rejected the male wasps after being stung.

When the experiment was repeated with the genital spines removed from the wasps, the tree frogs did not hold back and ate them without hesitation.

“The difference was statistically significant. Even a small difference in survival could prompt the development of anti-predation devices in insects,” Sugiura said.

According to Sugiura, little research has been done on insect genitals outside of their role in reproduction, although the wasp defense mechanism is not entirely without precedent.

For example, previous research has found that some species of hawk moths use their genitals to emit ultrasounds that interfere with bat sonar.

Sugiura is no stranger to uncovering some of the strangest ways animals evade their predators.

He has documented how some bugs, once ingested, are able to escape by following the digestive tract to its logical end and escaping from the anus.

And he showed that other insects can trick any unfortunate toad that ate them into regurgitating them.

He now hopes to expand his current research to see if other wasp families share the same genital sting defense mechanism.

© 2022 AFP