Unlike female bees and wasps, which use modified ovipositors used for egg laying to sting, male wasps were previously thought to be stingless and "were believed harmless".

The discovery was made when Kobe University academic and study co-author Misaki Tsujii was stung while studying the mason wasp.

The painful sting didn't match previous knowledge of the male wasp's defensive behaviour, that included mimicking the colour and behaviour of their female counterparts.

The researchers placed male wasps into tanks with predatory tree frogs.

Every wasp in the study was attacked by the frogs and over a third were spat back out, with recordings showing the wasps defending themselves.

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"Male wasps were frequently observed to pierce the mouth or other parts of frogs with their genitalia while being attacked," the study said.

Wasps with their genitalia removed and left without a means of defence were all eaten.

Co-author Shinji Sugiura said male animal genitalia had very rarely been studied in terms of prey-predator interactions.

"This study highlights the significance of male genitalia as an anti-predator defence and opens a new perspective for understanding the ecological role of male genitalia in animals," he said.

The researchers believe the discovery means the defensive tool could be found in several wasp species.