Ichneumon Wasp: That Long ‘Stinger’ Is Really an Egg-Laying Tube
It’s late spring, and a wasp lands on the trunk of a dying maple in your yard. Its body is an inch and a half long, and trailing behind it are what look like three tails several inches long. It’s hard not to assume the worst. But the ichneumon wasp you’re looking at is one of the least threatening wasps in Ohio. That long “stinger” is actually an egg-laying tube, and its target is inside the tree, not you.
What Is an Ichneumon Wasp?
Ichneumonid wasps are parasitic on other insects. The University of Minnesota Extension profiles the giant ichneumon, Megarhyssa, a large wasp found on declining or recently dead hardwood trees between May and July (UMN Extension). UMN describes two species: M. macrurus, reddish brown and yellow with black throughout, and M. atrata, black with an orangish head.
Identifying an Ichneumon Wasp
- Size: UMN gives a body length of about 1.5 inches and an ovipositor 2 to 3 inches long, for a total of about 4 inches.
- “Three tails”: The ovipositor has two protective sheaths, which UMN says makes the wasp look like it has three tails.
- Where you’ll see it: On the bark of dying or recently dead hardwoods, often with the ovipositor curled or pushed into the wood.
- Look-alikes: UMN notes it can be mistaken for other large insects like mayflies or dragonflies.
What That Long Tail Is For
Megarhyssa is a parasite of horntails, wood-boring insects that attack dying or recently dead hardwoods such as oak, maple, birch and elm. UMN explains that the wasp can drill a half inch or more into the wood with its ovipositor to deliver an egg into a horntail larva. When the egg hatches, the wasp larva slowly feeds on the horntail and eventually kills it, then the adult emerges from the tree.
It may look like the wasp is attacking the tree, but UMN is clear that it doesn’t injure trees. It only feeds on the horntail. If you’re seeing these wasps, though, the tree itself may be declining, and an arborist can tell you whether it’s a safety concern.
Is an Ichneumon Wasp Dangerous?
UMN says these wasps are harmless to people and ignore people when possible. If mishandled, one may jab with its ovipositor in self-defense, which generally results only in a minor wound. UMN’s advice: ignore them, and they’ll go away on their own. There’s no need to treat them with a pesticide, and there’s no nest for us to remove.
When It’s Not an Ichneumon Wasp
Ichneumon wasps don’t build paper nests or defend a colony. If you’re seeing many wasps flying in and out of one hole in the ground, a gap in the siding or a gray paper nest, you’re dealing with social wasps such as yellowjackets, paper wasps or hornets. Those are the ones worth a call. Compare them in yellowjacket vs. paper wasp and identifying a wasp nest by shape.
Frequently Asked Questions
Is this the “murder hornet”?
No. See giant hornets and Ohio for what that insect looks like.
What other harmless wasps might I see?
See potter and mason wasps, blue-winged wasps and great black and golden digger wasps.
How do I tell wasps, bees and hornets apart?
Start with our Ohio identification guide.
Still Not Sure?
Send a photo to Northwest Ohio Wasp Removal by call or text at 419-614-6445, or use our contact page. If it turns out to be a nest that does need attention, our wasp and hornet nest removal uses no pesticides.
