Scientists have long known that female bees and wasps use modified ovipositors – formerly used in egg laying – to sting their attackers. Now, a team of researchers led by Kobe University in Japan has found that male mason wasps use their sharp genital spines to attack and sting predatory tree frogs in order 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 study lead author Shinji Sugiura, an entomologist at Kobe University in Japan. “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.”
The scientists discovered this surprising ability of male wasps by accident. While studying the life history of the mason wasp (Anterhynchium gibbifrons), study co-author Misaki Tsujii, a professor at the same university, got stung. “Surprisingly, the male ‘sting’ caused a pricking pain,” Sugiura explained. “Based on her experience and observations, I hypothesized that the male genitalia of A. gibbifrons function as an anti-predator defense.”
Although wasps and bees are well known to use venomous stings to defend themselves and their colonies against predators, scientists have long thought that, because they evolved their venomous stings from ovipositors, males lacking these organs were harmless. Thus, feeling the pain after a male wasp sting was highly surprising.
To solve this mystery, the researchers placed male wasps in an enclosure with a potential tree frog predator. While all of the frogs attacked the male wasps, just over a third of them spit the insects back out – more specifically, precisely the male wasps that still had their genitalia. Thus, the scientists managed to witness the wasps stinging the frogs with their genitalia while being attacked.
These findings suggest the male wasps use their genitalia to sting predators and avoid being eaten. Since male genital spines (called “pseudo-stings”) are found in a variety of wasp families, this newly discovered defense mechanism is likely to characterize many wasp species.
The study is published in the journal Current Biology.
Image Credit: Current Biology/Sugiura et al.
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