Establishment and re-introduction of the field cricket into Southern UK

Summary

The field cricket (Gryllus campestris), one of the UK's rarest insects, had declined by the late 1980s to a single West Sussex colony of fewer than 100 individuals due to loss and fragmentation of its specialized grassland habitat, prompting inclusion in English Nature's Species Recovery Programme in 1991 with a target of establishing ten secure populations across its historic Southern England range. Because the surviving wild colony was too small to supply direct translocations, the Zoological Society of London developed an ex situ breeding program starting in 1992, collecting three pairs of sub-adult crickets from the wild each spring to breed large numbers of late-instar nymphs, maintained in isolated, disinfected rearing rooms with separate genetic lines to preserve diversity before combining stock for release. Between 1992 and 2007, this program produced more than 17,000 nymphs for field establishment, achieving 80 to 90 percent survival to release stage, though pre-release health screening in 1996 and 1997 detected gregarine parasites that forced cancellation of releases in both years. Of seven established field colonies, four remained extant by 2007, the longest persisting to an eighth generation, while some other release sites proved too difficult to manage and required abandonment or re-introduction. The project rated itself Partially Successful, since the target of ten secure populations has not yet been reached and ongoing site management remains necessary to prevent colonies from declining as habitat conditions naturally shift toward unsuitability.