Bush crickets make the most of autumn sun

I try to make the most of any late-autumn warmth by getting out into the field, treating each warm and sunny day as if it might be the last one before the onset of winter. While a bright morning might start with a nip in the air, it often warms as the sun rises and the small numbers of summer insects that remain can be seen on the wing or crawling across the surface of some fading leaf. The warmth of last weekend drew me to the coast and to some of the small lanes that drop down towards the beach at places like Kelling and Weybourne.

One particular stretch of low hedgerow, dense with bramble and in full sun, was alive with the sounds of calling bush-crickets. It is late in the season for these insects and many of the Breckland populations have fallen silent over recent weeks, possibly due to the handful of night frosts that we have already experienced. Here on the coast, however, there were good numbers of Dark Bush-crickets repeating their short chirping song at irregular intervals. The song is high-pitched and while I can still hear it, my birdwatching companion no longer can. With patience I was able to locate a couple of the calling individuals and point them out. Each robust and dark individual, about two centimetres in length, was calling from just within the bramble cover, producing its call by rubbing its modified wings together.

Typically, in male bush-crickets, the base of each wing is modified, with a tooth-bearing rib present on the underside of the left forewing. This is rubbed against the edge of the right forewing, next to which is a modified area, known as the ‘mirror’, which amplifies the sound that is produced. Only the Oak Bush-cricket lacks this adaptation; the male instead tapping out his drumming call with a hindleg onto whatever he happens to be standing on.

Dark-bush Crickets are robust creatures and have a long season, lasting through until the first frosts of late October or November. However, other bush-crickets are more strongly influenced by temperature and so I was a little surprised to see and hear two calling Roesel’s Bush-crickets in the same stretch of hedgerow. Roesel’s Bush-cricket is a species that has expanded its range northwards over recent years, a result of global climate change. First recorded in Norfolk in 1997, its colonisation of the county has been extremely rapid. Hot summers can boost numbers and while the 2008 summer may not have been the best, the species has clearly been fairly successful. Let’s hope they continue to call for a few more warm and sunny mornings.

Dark bush Crickets

There was a stillness to the morning, a calm that had draped itself over the river, delivering an almost soporific quality to the air. The river flowed with a gentle ease, reflecting the lack of rain over recent days, as it murmured its way quietly downstream. Only the steady chirps of dark bush crickets broke the silence. These calls, with their resonant quality, had a tropical feel to them, something enhanced by the slightly humid air of this mild early morning. Every bush or piece of waterside vegetation seemed to host several crickets; each one was sat squarely like a little toad, squat in posture and dark brown in colouration. The short chirping call was an advertisement, directed at a potential mate.

I had come down through the meadows to collect two crayfish traps, set the previous evening. As I moved through the vegetation I could smell the umbellifers and that strange aroma that I have come to associate with wet meadows. It is an almost acrid scent, slightly unpleasant and vaguely reminiscent of a public lavatory, but with an underlying sweetness. I remember how the short-tailed voles, that I used to live-trap as part of a study into their ecology, also had this scent and how it clung to my clothes after early morning rounds of my traps. Did the voles acquire the scent through their diet or because they lived within the pungent vegetation? I am sure a botanist could tell me its source and the chemical nature behind it.

The two traps are packed with crayfish, despite being in the water for only a dozen hours, and it is clear that this section of the river still supports a very large population of signal crayfish. I have commented before upon the problems that this introduced species has caused, wrecking river banks, reducing fish populations and eliminating our own native species of crayfish. Although I am trapping these signal crayfish in order to monitor their numbers, and to test the effectiveness of different types of trap, I am not allowed to release them back into the river. Instead, they must be killed and so end up in a pot, cooked and then served with a garlic mayonnaise or forming the centrepiece of a pasta dish.

As I trudge back to the car with my bucket of crayfish, I become aware of another cricket calling. This is Roesel’s bush cricket, a large species with a distinctive high-pitched call. It sounds like a softly running fishing reel, of the old-fashioned style used for fly-fishing, and is one of the first sounds to disappear through the hearing loss than comes with age. I am glad that it is still part of my morning soundscape.