Submitted by AJ Cann on Thu, 25/07/2019 - 07:49
    Roesel's bush cricket

    In recent years we have become familiar with Roesel's bush-cricket, Metrioptera roeselii. Here's why...

    In the 20th century, Roesel's bush cricket was only known from the south east coast of England. Although this species has spread by gradual colonisation over short distances, it also has a secret weapon, the occasional appearance of macropters. Both males and females are normally brachypterous, with vestigial wings. However, a macropterous long-winged form, f. diluta also exists. These usually make up less than 1% of the total population, but in some populations occur in much higher numbers, usually in areas where the bush-cricket's range has recently expanded. These can fly some distance, unlike the mostly flightless normal short-winged form, spreading into novel territory and establishing new populations. Macropterism is thought to be triggered by population overcrowding, limited food availability, and warm weather, and in fact one may follow the other when warm spells lead to a successful breeding season and therefore a high density of nymphs the following year. Once a new population is established, the long-winged form quickly goes back to being rare since there is a trade-off between reproductive success and dispersal ability. In the wake of the European heat wave of 2003, one study found a high level of immigration by long-winged individuals into a previously unoccupied area in large enough numbers to overcome any genetic founder effects in the resulting population. This would suggest that one unusual year can indeed have a significant impact on the distribution of macropterous bush-crickets. Two unusual years in a row, presumably more so. 

    Yesterday evening I was in my Leicester garden when suddenly I was surrounded by a swarm of flying cricket. They're impressive insects when they fly and certainly attract your attention. I've never had this species in my garden so before, so this winged wonder was certainly colonising new ground. We occasionally get locusts in Leicestershire, and while it's possible that these may have flown in from their native lands, they are usually regarded as escapees from the pet trade, where the are bred in great numbers as food for reptiles. Flying bush crickets is probably as close as we'll come to seeing swarms of locusts in Leicestershire. Hopefully.