NIW Insect of the day: Wart biter cricket

Posted 24 June 2014

This Insect of the Day feature has been produced as part of Harper Adams University's National Insect Week celebrations, June 23-29.

The wart biter cricket by Senior Lecturer, Dr Andy Cherrill.

 

The wart biter bush cricket, Decticus verrucivorus, is one of the UK’s largest, rarest and most attractive insects. It is restricted to a handful of sites in southern England, yet most people will be familiar with the wart biter’s more common relatives - crickets, bush crickets and grasshoppers. 

The wart biter is named after its use as a traditional remedy for the removal of warts from the skin. The wart biter would be held against the wart and allowed to chew away at the blemish with its powerful mandibles.

The diet of the wart biter normally includes other insects and developing flower heads, with their protein-rich developing seeds. 

In the UK, the wart biter is protected under the Wildlife & Countryside Act from collecting and destruction of its habitat. It currently occurs at only five sites in two contrasting habitats: an acid heath in Dorset and calcareous grasslands in East Sussex, Wiltshire and Kent. The population in Kent is the result of the release of captive bred animals from stock reared at London Zoo and all populations are within nature reserves.

In addition to a plentiful supply of high energy food, the wart biter’s sites are managed to maintain a mosaic of vegetation heights including short turf and dense tussocks. Eggs are laid in areas of short turf and the young hatch in the spring and then develop through a series of seven intermediate stages (instars), before becoming adult.

Around the fifth instar, the young bush crickets show a marked change in behaviour involving a preference for dense tussocks – probably in part to avoid predation but also to help thermoregulation i.e. in controlling their body temperature by selecting suitable positions either in sunlight or in shady parts of the tussock.

Males attract females by ‘singing’ – a sound produced by rubbing the bases of the wings together. During mating, the male transfers a complex structure called the spermatophore to the female. This comprises two sections; a sperm containing ampulla attached to the female’s external genitalia, and a protein-rich food parcel called the spermatophylax.

Sperm drains from the ampulla while the female eats the spermatophore. She then removes and consumes the ampulla, including any undrained sperm. The spermatophore provides the female with much needed protein but its main function appears to be to prevent the female from removing the ampulla before sperm transfer is complete.

Numbers of wart biters are low – numbering only a few hundred adults even at the best sites – and fluctuate widely from year to year. The eggs take at least two years to hatch and in the laboratory a proportion do not hatch until the third, fourth or even fifth year.

The wart biter has a complex life cycle and habitat requirements. Unfavourable management and habitat loss have caused some populations to be lost but those remaining are now all within nature reserves.