DOES WATER MAKE A MANTIS SUICIDAL?

The mantis is always ready for battle. When it’s time to strike, the insect lunges for its prey within one-tenth of a second, trapping it firmly in front legs that are reinforced with spines and making short work of it. When it’s not attacking prey, a mantis will camouflage itself as a leaf or flower. It stays motionless like this for hours on end, and then out of nowhere it can spring forth, even plucking a fly from the air with its “death grip” arms.

The mantis is not too bothered by rain, but during a heavy shower it seeks shelter under the same leaf it was just imitating. The insect would also rather avoid deep standing water, and it will only paddle its way across shallow puddles when there is no other option. And yet, floating mantis corpses are a fairly common sight in lakes. Is this because of some mysterious form of mass mantis suicide? No, the culprit is the horsehair worm, a tiny parasitic organism. It nestles its own larvae in the larvae of a mosquito, for example, which in turn are eaten by the mantis. What happens next is not entirely clear to scientists: Somehow the parasite manages to tap into certain synapses in the mantis’s brain so that it A) loses its free will, and B) staggers toward water as if controlled by an external force. “Perhaps the parasite triggers a sensation of intense thirst in the mantis,” suggests entomologist Damir Kova.

Such a feeling of thirst is so extreme that the dewdrops on the leaves are no longer sufficient for the mantis. Once it arrives at a lake, the worm attacks the innards of the mantis, which finally falls into the water as a hollow shell. Having achieved its goal, the worm exits its host: The conditions for its reproduction are optimal in the water. Sometimes a mantis will not be entirely gutted by the worm, and after depositing its payload it may leap back onto dry land. Having escaped death so narrowly, it is likely to avoid large puddles in the future.