Given favourable weather, the first thing to do before attempting a survey is to tune in one’s ears to the selected site. Their superb camouflage against the sward renders eye-contact unlikely, hence the acoustic approach. Familiarity with the fairly unmistakable sound means that a few seconds of careful listening, amongst the background cacophony of grasshoppers, will isolate the stridulating song of our first male wart-biter. It’s a robust, almost metallic chirping that increases in frequency into a continuous trill, a bit like a bicycle freewheeling down a slope, as this bush cricket attempts to attract the females.
The wart-biter is one of the largest species of orthoptera (crickets and grasshoppers) in the UK. Its name is thought to come from a Swedish wives’ tale that they could be used to nibble off people’s warts. How this myth began is anyone’s guess, but they do have characteristically bulky orthopteran mandibles, which may have lent credibility to their reputed propensity as wart surgeons.
While their appetite for human papillomas may be exaggerated, their diet is certainly cosmopolitan. Both nymphs and adults feed on various grasses, herbs, flowers and insects, including other crickets and grasshoppers. Despite their broad diet and a generous distribution across Europe, the UK finds them at their northern extremes, and as with other such insects, these fringe populations are highly specific in their habitat requirements. As such, they’re unlikely to have ever been superabundant here, and numbers have declined over the last century due to habitat destruction and fragmentation.
Threat of national extinction
Sussex is their main stronghold in the UK, with four of the six known wart-biter sites occurring here, with an additional site in Kent and another in Wiltshire. British Wart-biters have become exclusively associated with high quality chalk grassland. They require a mosaic of open swards, the longer tussocky areas providing a platform for males to sing from as well as a refuge from predators, the shorter grasses allowing smaller nymphs to bask in the sun and areas of bare soil in which females lay their eggs. Adults are 3cm long and bulky, with relatively short wings that are virtually useless for flight, so all these habitat features must be present within a small area, preferably south facing as wart-biters are highly thermophilic. Oh, and coarse scrubby vegetation can be an impenetrable barrier to dispersal, even if it’s just a few metres to a neighbouring habitat patch. These crickets seem to be asking for national extinction.
In the 1990s, the Zoological Society of London, under the remit of an English Nature (now Natural England) species recovery programme, began to trial the captive breeding of wart-biters for reintroduction. Compared to the ease of a simultaneous breeding strategy for field crickets, wart-biters proved to be somewhat tricky customers to breed in captivity: the two-year incubation period of the eggs was rendered even less successful by the unhelpful cannibalistic tendency of the nymphs to eat one another.
While captive breeding success did improve, most current translocations source wild-caught individuals (mostly gravid females) from the country’s best population at Castle Hill near Woodingdean. Subsequent successful introductions to new sites include Deep Dean near Alfriston. Given the cricket’s two-year life cycle, this progress remains tentative, but so far so good.
A brighter future for wart-biters?
So, what does the future look like for wart-biters in Britain? Perhaps surprisingly, given the general trajectory of biodiversity and the wart-biter’s fussiness, there looks to be room for some optimism. The Changing Chalk partnership aims to restore areas of lost chalk grassland at the eastern end of the South Downs, one element involving increased monitoring of wart-biter populations and identifying potential reintroduction sites. Brighton & Hove’s City Downland Estate Plan will likely add to this habitat restoration.
Notably, wart-biters may be among those UK species to benefit from climate change, as more of the country becomes suitable for them, potentially enabling them to expand their geographic range. Such progress may well come at the cost of a population contraction in southern Europe, depending on the extremity of the climate change where the frequency of severe droughts may have adverse effects on their habitat structure.
In the long term, simply translocating individuals to new isolated and intensively managed sites, not unlike spreading chips indiscriminately around a roulette table, doesn’t seem especially sustainable. It is, however, a necessary starting point – intense management at specific sites to benefit a specific target species can often avert immediate risk of extinction. The classic Theory of Island Biogeography argues that small and isolated populations are usually more vulnerable than larger more contiguous populations.
What’s needed now is rewilding on a massive scale. It should be noted that chalk grassland is a man-made habitat requiring prescriptive management; wart-biters were here before it, and they will hopefully remain after most human management is no longer necessary. This should be the ultimate goal of biodiversity conservation: with a landscape boasting good connectivity between habitat and ecological dynamism, from the grazing and browsing of reintroduced large keystone herbivores, we could facilitate a reasonably interlinked national population of wart-biters. Their finicky requirements would become less problematic and reduce demands on human intervention. The Weald to Waves project, while not exclusively focused on the South Downs, is a good local example of thinking on this scale.
In the meantime, Buglife is looking to train a network of volunteers who can help to survey and monitor wart-biter sites, along with its other Changing Chalk projects. The wart-biter is a bright green jewel among Sussex wildlife, and it would be wonderful to see local people mobilise to support its recovery. Keep listening!