The beat of a bush cricket

I first found a Roesel’s bush-cricket in the summer of 2009 in the long grass of some set-a-side land behind the string of houses in our small hamlet. That land is now consumed into a garden, but I digress.

I came across one again the other week in the warmth of mid-September as Jasper and I ambled down the lane on one of our daily walks around our patch of the Rib valley. An unmistakeable unbroken stream of stridulations emanated from a patch of long grass in the thin strip of roadside verge.

Despite the strong breeze, bright sunshine beamed down from a clear sky which had managed to raise the temperature for this basking specimen to an optimum for stridulation. It was quite happy to continue as I moved my smart phone closer, so much so that I was able to shoot some video at both normal and slow motion speed.

 

 

 

 

On playback, particularly in slow motion, it is fascinating to be able to see the wing casing visibly vibrating or stridulating against the comb-like structures on the cricket’s legs to create the sound that we hear. 
When watching the video back I noticed what appeared to be quite large and somewhat tatty wings, which I didn’t remember as being so prominent when I had looked at them previously.

Compare this freeze frame from the video to the specimen below that I photographed in July 2009. No wings – vestigial or otherwise – seem to be visible. 

The answer I found was quite fascinating.
The bush crickets first emerge as nymphs in May from eggs laid the previous summer and autumn that have been placed into grass stems by the female, using their long ovipositer. The nymphs then grow and develop, shedding their outer skins in a series of 5 or 6 regenerations called instars, before a final metamorphosis into their adult form.

In most cases they are brachypterous, meaning they develop wings that are small, undersized and not at all functional in the normal sense of wing development. However in about 1% of the species, the adult emerges in a macropterous form with fully formed wings. This would give an obvious advantage to both individuals and the species in general in extending it’s range by easier dispersal from the home environment and is thought to be due to reduced levels of juvenile hormone in the final instar, brought about by increased population pressures in the local environment. A beautiful in-built biofeedback loop, developed through evolutionary pressure that gives the species an opportunity as a whole to move about the landscape.

References 
Gardiner T (2008). The Overlooked Orthoptera: an introduction to grasshoppers and bush-crickets. Essex: A British Naturalists’ Association Guide.
Marshall JA & Haes C (1988). Grasshoppers and Allied Insects of Great Britain and Ireland. Great Horkesley, Colchester, Essex: Harley Books.


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