Monday, September 1, 2008

Come to the wonderful field, Grasshopper.

At Terra Nova, which is in Richmond, there is a field set aside for wildlife. It is a wonderful field that contains a man-made pond for waterfowl, and perching posts for raptors. It is surrounded by a ditch, which serves as a protective moat, and this is bordered by a gravel footpath, where I have seen coyote pups playing. Most often though, you meet only other suburbanites walking with their dogs, or their iPods, or both.

We were near Terra Nova yesterday, and I suggested to my son that we take a walk around the field. No coyotes this time, and few birds. It is not that time of year. But there was one zoological signal of late summer: grasshoppers.

Every few metres our steps would—surprise!-- launch a brown woodchip, which would sprout wings and clatter through the air a few seconds, then fold back into a woodchip, fall to earth, and disappear.

“What are these things?” son asked.

“Some kind of short-horned grasshopper,” I said. My guess now is genus Trimerotropis, but I had no idea at the time.

I watched him learn to spot where they landed, and sneak close before they again shot into the air. But he never got within grabbing distance, so hasn’t yet learned the other surprise, tobacco-juiced fingers.

We got to a platform at the edge of the ditch, which overlooks a gap in the trees and reveals the pond. The pond contained a few mallards, nothing else. Then son said, “Here’s another grasshopper. A different kind.”

Indeed it was. My guess now is genus Melanoplus, which makes it also a kind of short-horned grasshopper, although this one is in the subfamily Melanopilinae, whereas Grasshopper 1, if correctly identified, is in the subfamily Oedipodinae. These are both subsets of the Family Acrididae.

Notice how our friend Melanoplus is investigating that cluttered groove between the boards of the viewing platform. She quickly, urgently, spun and jammed her abdomen down into the pebbles, sawdust, sand kicked from boots--whatever substrate was there.

Yes, she had chosen this of all places as a spot to lay her eggs. Grasshopper egg-laying is fascinating, because the female extends her abdomen several times its normal length to place her ovipositor deep into the soil. This is done using a rhythmic series of extensions and contractions of the abdomen that increase the elasticity of the pliable membranes between the sclerotized abdominal segments. I remember this from a film we used to show at the beginning of a functional morphology course for which I was the teaching assistant. I tried to find a paper related to what was shown in the film, but was only able to find this tantalizing abstract from an earlier study:

Mechanism of Abdominal Extension during Oviposition in Locusta.
J. F.V. VINCENT & SONYA D. E. WOOD. 1972. Nature 235, 167 – 168.

“THE adult female of Locusta migratoria digs a hole about 8−9 cm deep in sand in which to lay her eggs. The normal length of the ovipositing part of the abdomen is about 2.5 cm. Part of the increase in length is achieved by unfolding the telescoped intersegmental membranes, giving a two-fold extension. The rest of the increase is achieved by stretching a thickened part of the intersegmental membrane1 (Fig. 1A and B) by up to ten times the unstretched length. The possible mechanisms involved in stretching the abdomen, and some of the mechanical properties which might be expected of the intersegmental membrane if the proposed mechanism for extension is correct, are discussed.”

Oh, please don’t stop there!

Needless to say, we could not see the up to ten-fold abdominal extension—which may be just as well, because in truth it is a little revolting--and after a while felt a bit ashamed for staring at Madame Melanoplus, who deserved some privacy.

So we happily continued our way around the wonderful field at Terra Nova.

Tiddly pom.

The wonderful field.

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