Wild Profile: Meet the stump stabber wasp

Published: September 1, 2020

A female stump stabber was on a rock By koohlman/Shutterstock

The stump stabber wasp (a.k.a. giant ichneumon wasp) looks terrifying—check out that massively long stinger! But wait: that “stinger” is actually an ovipositor that the female stump stabber uses to pierce trees. Once she’s used the long appendage like an auger to drill into the wood, she deposits her eggs.

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Ichneumon wasps—there are about 2,500 known species in Canada—are parasitic. They may not be a threat to people, but they sure are to their insect or spider hosts. Stump stabbers parasitize the larvae of another non-stinging wasp, the pigeon horntail. Pigeon horntails are “wood” wasps; their grubs feed on weak, dying trees.

Here’s how the nightmarish cycle of life works: the stump stabber female locates horntail grubs by tapping on a tree trunk with her antennae and picking up the vibrations of the larvae as they move around, chewing, inside. She takes about half an hour to drill into a larvae tunnel, then deposits an egg near, or on top of, an unsuspecting grub. It will become a baby stump stabber host. Her egg hatches, and the ichneumon larva emerges only to eat into the horntail grub, using the host body as food. The wasp larva consumes the grub from the inside out, in about two weeks, before pupating for the winter.

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Gah, that’s gruesome. But no matter how freaky a female stump stabber acts, or looks—she’s up to 14 cm long, including the ovipositor; males are about a quarter of this size—at least the chances of getting stung by one are basically zero. (Stump stabbers stab stumps. Not people.) The ovipositor is specifically designed to lay eggs and doesn’t deliver venom, unlike the stingers of other wasps. Ichneumon wasps also aren’t attracted to food, sweet smells, or garbage in the same way as, say, a yellow jacket—so you may never even see one unless you know where to look.

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