An “unholy alliance” between rabbits and Australian redback spiders is threatening the existence of an endangered New Zealand species, a study led by AgResearch has shown.
Carried out with the Department of Conservation (DOC) and University of Otago, the study has illustrated the struggle for the ongoing survival of the Cromwell chafer beetle – a nationally endangered native species that can now be found only in the 81 hectare Cromwell Chafer Beetle Nature Reserve between Cromwell and Bannockburn, in Central Otago.
The study found numerous rabbit holes that provided shelter for the rabbits were also proving ideal spaces for the redback spiders to establish their webs. Investigation of those webs in the rabbit holes found the Cromwell chafer beetle was the second-most commonly found prey of the spiders.
These findings “give a fascinating insight into the almost accidental relationships that can develop between species in the natural world, and how that can impact on other species,” says AgResearch Principal Scientist Dr Barbara Barratt.
As a result of the research, DOC has carried out a programme to break down old rabbit holes and hummocks in the reserve to destroy spider nests, and does regular rabbit control. An annual survey for beetle larvae with AgResearch will show whether these actions are having an effect.
Beetle larvae will be surveyed next summer to see what effect reducing redback spider nests is having on the Cromwell chafer beetle.
The Cromwell chafer beetle (Prodontria lewisi) is a large flightless beetle that lives underground in the sandy soils of the Cromwell river terrace. In spring and summer adult beetles emerge from the ground at night to feed on plants and to breed.