Bug of the Month September 2010: Giant Ichneumon

What IS this?
Location:  Southern Vermont
August 26, 2010 8:43 pm
This insect was on my porch in July. It died shortly after I saw and photographed it. Any idea what it is??

Giant Ichneumon

Hi KT,
We just posted another image of a different species of Giant Ichneumon in the genus
Megarhyssa, but your individual, Megarhyssa atrata, is the species most often reproduced in identification guides and entomology texts.  The black body with the accent markings of yellow face, antennae and legs make this an unforgettable insect, but the truly distinctive feature is the five inch long ovipositor of the female.  The female uses her ovipositor to deposit her eggs in the stumps of diseased trees that are infested with the wood boring larvae of the Pigeon Horntail, Tremex columba (see BugGuide), and we frequently receive images of female Giant Ichneumons drilling into stumps.  You may read more about Megarhyssa atrata in our own archive and on BugGuideBugGuide indicates on the genus page that the common name Stump Stabber is sometimes used.  In August 2007, we selected Giant Ichneumons in the genus Megarhyssa as our Bug of the Month, and we have decided that since three years have passes, we are clear to feature it again as the Bug of the Month for September with your letter and photographs.

Giant Ichneumon

Hi Daniel,
Wow, that’s awesome! Thank you both for the thorough response, and for choosing to feature my photos!
What a fascinating insect that is! It’s strange that I didn’t find any photos when I was surfing, but I probably wan’t entering adequate identifying words in the search. That was the first one I’ve ever seen, and I haven’t seen another since. Are they common in Vermont? They must be somewhat reclusive, as I have ‘hawk eyes’ when it comes to insects and spiders and the like. I am both fascinated by and enamored with them!
Thanks again! I’m heading to your site now!

Hi again KT,
They are not uncommon in Vermont, but like many insects, there may be a robust local population in an area, but seemingly identical conditions a mile away may have no individuals.

Addendum:  Giant Ichneumon Ovipositing
What kind of bug is this?

Giant Ichnuemon

What kind of bug is this?
Location:  Warwick, Rhode Island
August 29, 2010 4:17 pm
These bugs just showed up and crawl all over the dead tree on the side of my house the long antenna looking thing seems to maybe suck something out of the tree! I have never seen these before and they look like they could be 2inches long some shorter some longer! Its the end of August so we are slowly going into fall.
Thanks, Dawn Bergeron

Giant Ichnuemon ovipositing

Hi Dawn,
This insect is actually depositing eggs into the tree, not sucking something out as you thought. Several days ago we decided to make the Giant Ichneumon our Bug of the Month for September 2010 so we included information on how the female oviposits her eggs in the wood of dead and dying trees that contain the burrowing larvae of the Pigeon Horntail.  The Giant Ichneumon is a parasitoid whose larvae feed solely on the larvae of the Pigeon Horntail.  Coincidentally, yesterday we posted an image of a female Pigeon Horntail, another impressive non-stinging member of the order that includes wasps, in the act of oviposition.  Though we wrote a lengthy response, we were not able to include images of the actual egg laying or oviposition process.  Your photos clearly illustrate the process of a female Giant Ichneumon laying eggs, though your species is different from the species in the Bug of the Month posting, which is Megarhyssa atrata.  We suspect your Giant Ichneumon is Megarhyssa macrurus. We are going to combine your letter and images with the previously selected letter to be a joint Bug of the Month for September 2010

Giant Ichneumon Ovipositing

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