Subject: Female Megarhyssa Atrata
Location: St Paul, MN
June 25, 2014 9:13 am
After finding your great web site I learned the name of the bug in my back yard. They were on a tree we were cutting down. Because it seemed to be laying eggs I decided to leave the stump for a while. Attached are some photos you may use. It is interesting to me that I have never noticed these before.
Signature: DS in MN
Dear DS in MN,
Thank you for your most kind compliment. The ovipositing female Giant Ichenumon or Stump Stabber, Megarhyssa atrata, is one of the most iconic North American insects and her image has been used to illustrate even really early entomological tomes as well as many popular insect books with broad appeal to popular culture. Your images are stunning, especially the first one that depicts two individuals. Just exactly what is going on in that image is most curious. The tangle of bodies makes it appear that both females are trying to oviposit in the same location. The female Giant Ichneumon is able to detect the location of the larva of a Wood Wasp that is feeding beneath the surface. The larvae of Wood Wasps like the Pigeon Horntail will serve as the prey of the larval Stump Stabber. We have designated your submission as the Bug of the Month for July 2014.
A large Stump Stabber can have an ovipositor nearly five inches long, and one of your images captures the classic position of a female looping the organ as she drills beneath the bark to deposit her egg where the young will have a food source.
Update: June 26, 2014
Dear Daniel Marlos,
I just had to write one more time. The first set of photos I sent were of the first time I had seen a flying insect of its kind, today I went to see if they were still on the stump, I found a new type. See attached photos. The first photo is from my phone. The second and fourth photos capture an ant crawling -shows size a little better. I am excited to show these, I hope you can use them.
P.S. There were ovipositing female Megarhyssa strata remains (wings and part of a tail) left on the stump! I guess a bird had a good snack.
Wow, what a wonderful addition to the Bug of the Month posting. Your new Ichneumon is most likely Megarhyssa macrurus, and you can compare your images to those on BugGuide. Your observation and speculation about the bird is a very good guess. The female Giant Ichneumon is quite vulnerable while her ovipositor is buried deep in the wood, and she would not be able to easily fly away from a predator. We have also heard of female Giant Ichneumons getting stuck and being unable to withdraw the ovipositor.