Parasitic Wasp from Unknown Moth Pupa

2022 August 7

Near the end of June, Sam found this pupa (which at the time was alive and wiggly) in the garden soil. It is probably one of the owlet moths, probably one of the cutworms, but I couldn’t be any more specific than that because a lot of cutworm moths make pupae that look like this.

So, of course, I put it in a jar to raise it and see what kind of moth came out, so we could maybe make a better ID. And on July 4, 2022, this is what we got:

And, as you can see, this is not a moth. It had been scrunched up in the front half of the pupa, while filling the tail part of the pupa with its various wastes and leftover internal organs from what would have been the moth.

This looks like one of the classic Ichneumon wasps. This is a genus of at least 141 species in North America alone. Of the species that have photos on BugGuide, the one that has the closest match to this one is Ichneumon annulatorius. It has pretty much the same color pattern, is found in Michigan, and commonly emerges from its host in July.

Female ichneumons are generally known for having long, scary-looking oviposiors at the end of their abdomens, and this one doesn’t have anything like that, so it is probably a male. He has standard waspy mouthparts, and probably feeds on flower nectar like a lot of other adult wasps do.

While the females will hunt for caterpillars to lay their eggs in, the males will be hunting for the females. Regardless of which they are looking for, those long, thready antennae have a lot of surface area and are very useful for sniffing out the odors of that which they seek.

Ichneumon wasps will prevent a lot of caterpillars from growing up, because they lay a single egg in each of their prey, so each mother wasp will hunt out as many caterpillars as she can find. This doesn’t do much to suppress the caterpillar population in the first year, because the caterpillars will still do all their damage in the garden before they pupate. But, it really reduces the number the next year, because now many fewer caterpillars are going to mature into egg-laying moths, and a lot fewer eggs will get laid. So the ichneumons are more of a long-term pest control solution. Which, unfortunately, you can only take advantage of if you forego spraying broad-spectrum pesticides this year, so that you don’t kill off the ichneumons before they can get the caterpillars.

Of course, there are pesticides and there are pesticides. If you use things like insecticidal soaps to kill caterpillars, they only kill the ones that they contact right away, with the residue washing off and decomposing. This is much less likely to kill ichneumon wasps. The adults come in, lay their eggs, and leave, and so they are probably not going to be there at the exact instant that you are spraying on the soap. So, you don’t have to completely give up to a massive caterpillar infestation, you just want to address it with something that is less likely to take out the caterpillar predators and parasitoids at the same time.

2 Responses
  1. Gaurav permalink
    August 12, 2022

    Hi Tim. I am leaving this comment here as I could not find a way to email you. You may choose to publish it or let it be.

    I am Gaurav from Ontario, Canada. I am very interested in the nature space and would like to offer to buy your site, if you are willing to sell it.

    If you are willing to consider selling, I will be happy to get on a Zoom call with you to figure out how we can work it out.

    Best regards

  2. October 16, 2022

    Gaurav, have you ever considered investing in the crazed Catholic nutjob space? Think about it. The growth possibilities are substantial. Have your people call my people. I think we can do a deal, baby.

Comments are closed.