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Bugguide looks like a very cool place to hang out for someone like me. Not really knowledgeable about insects and spiders but very willing to learn.

I only saw these Megarhyssa on two days...in the evening on an old maple. A week later the maple had been cut down by the city.

Thankyou for the warm welcome.

Robert Ganz

these wasps parasitize horntail (sircidae) larave that are found in wood that is dying or dead. That is why they are not found all over the place. They are very specific on their hosts. If you are interested in learning more, a great great resource is Insects: Their Natural History and Diversity, by Stephen A. Marshall. I recommend this book for anyone starting in insects, or seasoned vets. Has great great photos and easy to understand keys. Check it out on amazon.

Hello, we have a silver maple which dominates our back yard and is much beloved by our family. There are ichneumomoidea depositing eggs in one particular large branch. Does this mean the tree is dying? Will these wasps harm the tree? Thank you so very much!

I'm not a tree expert by any means, but I'm somewhat familiar with some of the natural history here...and I certainly don't think the wasps can be hurting the tree. They would only be ovipositing on the tree if they sensed that there are horntail larvae under the bark feeding on the tree. The horntails would be causing more damage, and the Megarhyssa would be helping limit the horntails numbers. In that sense, Megarhyssa are generally considered beneficial insects.

If the number of horntails is not too large, and your maple seems fairly healthy otherwise, I'd think there's nothing particularly ominous about your tree having some horntail larva present and the attendant Megaryssa activity.

But if the tree is old and senescent (i.e. approaching death on its own) then that will often attract attention from more horntails and other pests (as older trees begin to lose their ability to fend off herbivores and pathogens as effectively as younger ones). If that's the case, what you're seeing may be a symptom indicating your tree is entering its last years. But the horntails (and certainly the Megaryssa) would be less of a cause, and more of an effect (of senescence).

Hope that makes sense...and that your beloved maple fares well :-)

My kids are very happy that these crazy-looking insects are not hurting our "favorite tree". Thank you very much for your insights!

They are laying their eggs on the things that are living in the tree, often Tremex larvae

The Megarhyssa larvae will consume the Tremex larvae, not the tree. Click on Megarhyssa and then on Info to learn more.

if it has been entered on BugGuide. First, click on Search. Then select book and type Marshall, and search will return a link to the book. Click on the link and you will see that the book is assigned number 55904. Simply put Cite:55904 inside of square brackets and you will get a link to the book page like this (1). Nice eh!

Wow is right! I just saw, either this very same species or one very like it, ovipositing this afternoon. I live in Madison, Wisconsin, and this was in the University of Wisconsin Arboretum. I'm better at plants and birds than insects, but I was fascinated. Saw exactly what you captured in your photos: after she curled up her abdomen and inserted her ovipositor into the tree bark, a sort of translucent bubble developed at the tip of her abdomen. Is that an egg sac of some kind? Anyway, thanks for confirming what I saw.

...see the comment at the bottom of the previous image in this series. If you want even more info...check out this truly wonderful web page which provides great videos and links to further references.

What a marvelous creation of nature...and a masterful series of photographs here!!