Researchers at Kobe University in Japan reported a surprising defensive mechanism in male stonemason wasps. Their study, published in Current Biology, shows that these males possess retractable genital spines on either side of their reproductive organ, which they can deploy to deter predators.
Unlike female bees, male mason wasps do not carry venom or the ability to sting. For a long time, this led to the assumption that males were more vulnerable to threats. The new findings reveal a different reality: the male stonemason wasp uses two slender, retractable spines near its genital area to aid during mating, and potentially to fend off attackers where appropriate.
Early work in the laboratory focused on the life cycle of hornets. During one observation, a researcher felt a sharp sensation while holding a male insect, prompting a closer look at defensive adaptations. The investigative team designed experiments to uncover the source of this sensation.
In controlled conditions, Japanese tree frogs were introduced to containers housing male stonemason wasps, with cameras set to capture what occurred. The researchers observed that when predators approached, the wasps would display their pointed appendages in a defensive posture. In instances where a frog attempted to consume the wasp, the spines could cause injury, leading to an escape response by the predator.
Across 35.3 percent of observed encounters, tree frogs rejected the wasps and withdrew. The study team replicated the experiment using male hornets whose genitalia had been removed, noting a markedly different interaction pattern. The results suggest a functional role for these spines in predator interactions, even if not all encounters end in a stinging response.