Stump-stabber. An Ichneumon wasp at work.

While our daughter volunteered at Fort Edmonton on a weekend in May, 2010, my wife and I roamed the river valley around the fort. As usual I carried my camera equipment with me, setup for macro photography with diffused flash. While we paused to rest at a bench, I noticed a slender wasp ‘feeling’ its way across a fallen log. The “feelers” were vibrating – a movement accentuated by the white bands midway on the antennae.

I slowly went to my knees, doing the bug-whisper thing (…don’ fly away, don’t fly away, pleeeease don’t fly away!)  I cautiously adjusted my equipment and began taking pictures as she explored the wood surface. Within moments she was raising her abdomen and her ovipositor began ‘drilling’ into the wood.

The log was very close to the fixed park bench, and I struggled to keep her in the same plane as the camera — in this case it would have been an impossible task without the use of a right-angle viewfinder attached to the viewfinder of the camera. Her ovipositor slowly descended into the wood, leaving the protective sheath looped up behind the wasp.

She was now intent on the task, so I moved in as close as my lens would allow, capturing the detail of the ovipositor as it entered the wood.

She spent what seemed like a few minutes in that position, her ovipositor completely hidden in the wood. Then she began to move, drawing her abdomen upwards and slowly removing the ovipositor.

She turned, gave the ovipositor a quick cleaning with her hind legs and then went on the search again, her antennae tapping along the log like a blind person with a cane.

At this point I decided to try to see if I could obtain video of her behaviour, but the movements to remove my point and shoot camera from its case seemed to startle her and she flew off. I waited to see if she would return, but to no avail. (There, on my knees, I realised how valuable the then new video-ready crop of DSLR’s could be…)

What was she doing laying eggs in the log? Ichneumon wasps are parasitic, so I knew she was depositing her egg directly on or in a larva of some sort within the log. I emailed a picture to the ever-helpful AlbertaBugs listserv, and it was not long before I received a reply. Marla Schwarzfeld, at the University of Alberta, identified it to the genus Echthrus in the subfamily Cryptinae. She noted that the “…funky inflated front tibia” (see below) are features found on the females of this genus.

Marla’s I.D was a starting point for further research. (Without academic access privileges, I could not find complete research documents, but often the abstract or first page information provided an outline of what was happening.) The vibrating antennae were actually tapping the wood, a form of vibrational sounding (echo-location) ¹. This is where the enlarged tibia come in, as these have been shown to be capable of sensing the vibration of the returning echoes². The female ichneumon’s vibrating antennae are testing for the hollow passages in the wood where grubs are burrowing. Once she locates a grub, she pierces the wood with her ovipositor, and then places an egg on, in or near the grub. When the egg hatches, the larva will begin to feed on the grub, eventually killing it. The ichneumon larva will then pupate and eventually emerge from the wooden passage.

Darwin, when considering the claims of a beneficent intelligent designer, used the ichneumon as one example of why he could not believe this:

“But I own that I cannot see, as plainly as others do, & as I sh^d wish to do, evidence of design & beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice.”

Darwin Correspondence Project, “Letter no. 2814,” accessed on 24 February 2023, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-2814.xml

The Ichneumonidae…slim, elegant wasps whose parasitoid efficiency helped support a grand idea that was to shake a god-fearing world.

N.B. 10 June, 2010 — an email (as forwarded by Robin Leech) from Andrew Bennet (Ag. Canada) in Ottawa confirms it as genus Echthrus and adds: “… the genus parasitizes wood borers, especially Cerambycidae.” (Longhorn Beetles)

NB. 23 February 2023 — this article is a modified repost of an article first published on my now defunct blog, The Bugwhisperer on the 8 June, 2010, A full set of images can be seen at my Flickr site. The camera used for this was our first DSLR, the Nikon D70 (6.3 Mp), the lens was Tamron’s affordable 90mm macro and the flash system was Nikon’s awesome Nikon R1 Close-up Speedlight Remote Kit.

¹Laurenne, Nina, Nikos Karatolos  and Donald L. J. Quicke. Hammering homoplasy: multiple gains and losses of vibrational sounding in cryptine wasps (Insecta: Hymenoptera: Ichneumonidae). The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 82–102.

²Broad, Gavin R.  and Donald L. J. Quicke.  The Adaptive Significance of Host Location by Vibrational Sounding in Parasitoid Wasps. Proceedings: Biological Sciences, Vol. 267, No. 1460 Dec. 7, 2000, pp. 2403-2409

³Darwin, Charles. A letter to Asa Gray, 22 May 1860