Saturday, September 15, 2007

An Ichneumonoid Wasp Netelia testacea

I am an amateur naturalist trying to identify everything living in my garden.

Photo 1: "I vant to drink your blood!"

Actually, that's not true at all! If you're unfortunate enough to be a caterpillar however, he (/she?) wants to do something even worse to you! Read on:

On the same evening as I met the Brimstone moth in my previous posting, the red wasp in the photo was also fluttering around my night light. Photo 2 (click on photo's to enlarge) shows my wasp's beautifully slender waist and photo 3 (shot from below) his/her long antennnae.

Using the colour plates in Michael Chinery's excellent "Field Guide to Insects of Britain and Northern Europe" (Collins, 3rd Ed.) I've been able to identify my wasp as a member of the Ichneumonidae family of wasps. The Ichneumonidae are parasitic wasps in the grizzly business of laying their eggs on, or inside, caterpillars. In the latter case, when the eggs hatch the unfortunate caterpillar, often still alive, is eaten from the inside out. For those with strong stomachs, this site has lots of quality images of unfortunate caterpillars being variously parasitised.

As I repeatedly discover for the creatures on this site, it seems that a certain Charles Darwin has beaten me to comment. He was so struck by the grizzly business above that in an obscure little book (!) entitled 'On the Origin of Species' (you can find the complete, searchable text on the excellent Darwin online site incidentally) he wrote:

"to my imagination it is far more satisfactory to look at ...the larvae of ichneumonidae feeding within the live bodies of caterpillars,- not as specifically endowed or created, but as small consequences of one general law...namely, multiply, vary, let the strongest live and the weakest die."

If he keeps up his hobby, who knows, one day his natural-history writings may be as famous as mine (hem, hem!).

As every amateur naturalist knows, a bewildering array of insects can be found in the average garden. The question arises therefore, how do you know when you've found a Ichneumon wasp? Common features are long antennae and the long slender ovipositor, as with hoverflies however, ultimately identification rests on an analysis of the venation of the wings. Photo 4 (you'll need to click to enlarge) highlights the wing vein that, as I learn from Micheal Chinery's book above, indicates my wasp is indeed a member of the family Ichneumonidae.

Incidentally, I in no way harmed the wasp in photo's 2 and 3. He/she was released back into my garden after I'd taken my snaps. I can only ask that you take me on trust when I explain that by complete coincidence, 24 hours later, I found a superficially identical dead wasp on the upstairs carpet in my house. It was he/she who contributed the wing to photo 4.

When it comes to an identification of a particular species of Ichneumon wasp, as with beetles, things are much more tricky. There are some 3200 British and Irish species species (and more than 12000 worldwide). Gavin Broad has added an online checklist to the Biological Records Centre database. Based on the colour plate in the book above and its description as:

"one of our commonest ichneumons...Adults often come to lighted windows"

I'm going with the identity of my wasp being Netelia testacea. Unfortunately, as the book adds however:

"Ophion species are superficially very similar, but their venation is slightly different"

and indeed, googling Ophion yields pictures of wasps very similar to mine. Sadly the book gives no further details on separating Netalia from Ophion species. Gavin Broads has helpfully added a pdf key to Ichneumons to the BRC database, but, as he admits in the introduction,

"Identifying ichneumonids can be a daunting process...".

As an amateur I feel I'm lacking in the time (and very likely the skill) needed to work through the several dozen pages of microscopal details in the key. If anyone can confirm or deny my guess at Netalia testacea based on the face- and wing-images above therefore I'd be grateful.

Finally, a word on antennae! Insect antennae fascinate me. Using these tiny flexible rods, I read accounts of insects' ability to detect mating partners and food, sometimes from miles away. For no more reason than simple fascination value therefore, photo 5: a closeup (x100) of the tip of my wasp's antenna. Another of mother nature's tiny miracles.


Bart said...

I've been collecting Ichneumonids for years and have never been able to find a decent key for North American subfamilies let alone species. The wing venation is exactly like all of the Netelia I've seen though so you're on the right track.
Well written accound my friend!
Another thing I've been trying to do for years is take a good photograph. Any suggestions?

Henry Walloon said...

Thanks for the comment Bart.

My photography equipment is decidedly humble: a cheap Olympus 'holiday snaps' digital camera, held up to the eyepiece of student-edition microscope.

My only "secret" is to simply take a few dozen snaps of each scene and select the best.

Barry and Judy said...

Last night a strange looking creature showed up in our house (in the Sierra Nevada foothills) trying to escape at a window. After getting a pretty good look at it, I cupped it in my hands and was heading toward the door when it stung me. I promptly dropped it, and we couldn't find it again. This morning we found the creature again on a window, and we pulled out our "bug" books. We pretty quickly identified it as an ichneumonid in the genus Ophion or Netelia, but the diagnostic difference that stood out was that Netelia can sting and Ophion can't. So, if you find another, maybe all you have to do is pick it up and harass it a little to make sure which genus it belongs in.

From California Insects (by Jerry A. Powell and Charles L. Hogue), page 324:

"Netelia are similar [to Ophion] in general appearance and habits, being nocturnal parasites of cutworms. They are often attracted to lights and are sometimes confused with Ophion, but Netelia can deliver a formidable sting." And, in the Ophion description, "Although frightening in appearance, they do not sting."

Brock said...

Your wasp is actually an Ophion (very different wing venation from Netelia!).

Richard said...

The absence of a vein at the bottom left of the red square in your wing veination pic tells you it's Ophion, not Netalia - see on how to split the two genera.

My blog also lists where you can get ID guides/keys online: