An ''accidental relationship'' is threatening Cromwell's chafer beetles, as redback spiders living down old rabbit holes further threaten the existence of the endangered species.
AgResearch yesterday released a statement yesterday saying a study showed an ''unholy alliance'' of redback spiders living in old rabbit holes in the Cromwell Chafer BeetleNature Reserve.
The joint AgResearch, Department of Conservation (Doc) and University of Otago study found the rabbit holes were proving ideal spaces for the redback spiders to establish their webs; 99% of the spiders had built their webs in the rabbit holes.
Investigation of those webs in the rabbit holes found the Cromwell chafer beetle was the second-most commonly found prey of the spiders.
AgResearch principal scientist Dr Barbara Barratt said the findings gave ''a fascinating insight into the almost accidental relationships that can develop between species in the natural world'', and how that could impact on other species.
The development illustrated the struggle for the ongoing survival of the chafer beetle, which was a nationally endangered native species now found only in the 81ha reserve, between Cromwell and Bannockburn, Dr Barratt said.
She said it was not known how many of the chafer beetles were left, because they were not easy to find.
However, research into larval densities showed the numbers were low, and as redback numbers were increasing, this further increased the risks for the beetle population.
Cromwell chafer beetles caught in a web at Bannockburn.
The research showed that filling in the rabbit holes was an effective way of eliminating the spiders, and Doc had carried out a programme to break down old rabbit holes and hummocks in the reserve to destroy spider nests.
An annual survey for beetle larvae would show whether that had an effect on the redback population, Dr Barratt said.
