Wednesday, 21 July 2010

Cricket anyone?

There is a steady and penetrating buzzing sound that provides the soundscape to these lazy days of high summer, a sound that is not so very different from that which I have sometimes heard from electricity pylons during damp weather. This, however, is not a man-made sound but the song of an insect. The insect in question is Roesel's Bush-cricket, a large and distinctive species that was first recorded in Norfolk in 1997. These magnificent ‘wee beasties’ have done well in the Brecks now that they have become established here, part of a range expansion that has seen them spread across much of southern Britain in a short space of time.

Experts believe that this bush-cricket is a relatively late post-glacial colonist, with a long-standing population established within the Thames Basin, and with outlier populations in Wales and Ireland thought to be relicts of an earlier invasion that took place before the establishment of the 'wild wood' cover that dominated these islands for many hundreds of years. Even as recently as 1988, the range of this species within Britain & Ireland was still very much restricted to these geographically separated sites. Then it all changed, with a run of ideal summer conditions providing the impetus for a movement north and west.

I recall their arrival in the Brecks and discussions about just how far north they had spread across the county. These days there are few bits of rank grassland around here that do not buzz to their song during these hot summer months. Not everyone can hear the song, as the ability to detect these higher frequency noises tends to be lost as we get older. A friend of mine lost his ability to hear their call a couple of years ago and now relies on either his bat detector or the ears of his two young daughters to pick them up. Even if you can hear the song, they can be difficult to pin-point and see well. The males quite often deliver their song from towards the top of a grass stem but the song has something of a ventriloquistic quality and it can be difficult to home in on the bush-cricket itself. I find that cupping my ears and then rotating my head slowly from side to side, while facing in the general direction of the sound, usually helps. Once you have spotted your bush-cricket you need to approach with care as the males have a habit of dropping down into the vegetation if disturbed. A good view will reveal the diagnostic prominent cream-coloured line that runs around the margin of the pronotum (effectively the middle section of the body) and a sturdy and surprisingly large insect.

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