The ‘Stump Stabber’ – An Ichneumon Wasp

Echthrus sp., Family Ichneumonidae

Tap, tapping with antennae

While our daughter volunteered at Fort Edmonton this last weekend, my wife and I roamed the river valley around the fort. While we paused at a bench, I noticed a slender wasp ‘feeling’ its way across a fallen log. Its antenna were vibrating – a movement accentuated by the white bands 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 adjusted my equipment and began shooting 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 my

Drilling begins

right-angle viewfinder. 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 man 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 new video-ready crop of DSLR’s could be…)

The 'sheath' loops back...

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 group, and it was not long before I received a reply. Marla Schwarzfeld at the U of A identified it to the genus Echthrus in the subfamily Cryptinae. She noted that the “…funky inflated front tibia” (see photograph in previous article) 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 or echo location¹. This is where the enlarged tibia come in, as these have been shown to

Ovipositor at maximum depth

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 beneficient 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.”

Cleaning the 'sheath'

The Ichneumonidae…slim, elegant wasps whose parasitoidan organism that lives in or on the body of a single host individual, eventually killing that host. efficiency helped support the grand idea that shook a superstitious world.

For more photographs of ichneumon wasps, visit ZipcodeZoo.com

N.B. 10 June, 2010 – 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.” (the Longhorn Beetles)

²Broad, Gavin R.  and Donald L. J. Quicke.  The Adaptive Significance of Host Location by Vibrational Sounding in Parasitoidan organism that lives in or on the body of a single host individual, eventually killing that host. Wasps. Proceedings: Biological Sciences, Vol. 267, No. 1460 Dec. 7, 2000, pp. 2403-2409

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