The Worm That Controls the Praying Mantis

If karma can apply to insects than the special relationship between the praying mantis and the hairworm has to illustrate it better than most. The praying mantis is a beautiful but ruthless creature. It’s predatory, hungry and looks evil with its’s 180 degree rotating triangular head, long front limbs with spikes and jaw-dropping reflexes. This is a creature that feasts on a variety of small insects such as moths, grasshoppers, crickets and flies.

The mantis usually lies in ambush, completely still, while it waits for its next meal. With a long green or brown body, the mantis is well camouflaged in its natural habitat. Once its beady compound eyes have latched onto its latest prey, it’s usually not long before that insect is warming the mantis’ belly. With spikes attached to its front raptorial limbs, any hapless prey is quickly overcome. Pinned down and helpless, the praying mantis consumes its prey greedily. It even has three simple eyes at the back of its head. What could stop this king of the insect predators?


Praying Mantis
Praying Mantis. Credit: Lazydaz/ Dreamstime

Controlled by a worm

Unfortunately the praying mantis is also a victim of its own success. The prey it eats can often wreak its revenge from beyond the grave. This can happen if the prey taken is host to the microscopic larvae of the parasitic hairworm (Chordodes formosanus). When the praying mantis eats an infected insect, it also consumes the hairworm larvae, which starts to grow rapidly inside it.

Before long the abdomen of the praying mantis contains a hungry hairworm several centimeters long. This hairworm has one aim, to reach sexual maturity and reproduce. It needs water to do this; so as well as chewing on the mantis from the inside it secretes proteins which seize control of the mantis’ nervous system. Not only is the hairworm consuming the mantis from the inside and turning it into a husk, it’s also able to order it around.


Parasitic hairworm emerging from praying mantis. 


By the time it has reached sexual maturity the hairworm can be as much as one meter long. Needing water to reproduce, the hairworm orders the poor mantis into water so it can be excreted. Befuddled, the mantis proceeds to drown itself in the nearest body of water; a sort of watery suicide by proxy. Like some creature in a science fiction movie, the hairworm escapes through the anus of the mantis, looking to breed.

By the time the hairworm leaves its rear end the mantis is little more than a shell. The hairworm can only reach full maturity by hollowing out the mantis completely, even if that means eating all the internal organs. Even then it must pack itself tight inside the mantis’ abdomen.

Impact on reproduction

Not that it will care too much at this stage, but the male mantis will also by now be suffering from shrunken testes. Its opportunities to reproduce – unlike the hairworm – have been thwarted. The hairworm optimizes the energy it draws from the male mantis while in effect castrating it. By doing this it even prevents the stricken mantis from passing on its genes before it perishes.

If the mantis is female, reproductive capabilities are not diminished by the parasite – it can still produce offspring. It’s not known why there is this bias between male and female mantis hosts. Scientists suspect it may have something to do with how the hairworm tampers with development hormones. Males may keep more juvenile qualities than females, although both sexes when infected appear smaller and less adult.

A deadly and efficient parasite, Chordodes formosanus helps balance out the karma within the insect kingdom. The ferocious praying mantis can be humbled by a simple worm, which once ingested rots it from within.