Taken from the Massey University website; here are some notes on New Zealand "slaters".
Slater bodies are heavily armoured with calcium carbonate and are quite rigid. The body is divided into three regions - head, thorax, and abdomen, but these are far less distinct than the head, thorax, and abdomen of insects. Overall, the body has a smooth, rounded outline.
Slaters are mainly scavengers. They are omnivorous, feeding on a variety of decaying vegetation, tree bark, rotting wood, etc. Slaters may also graze on fungi associated with decay, or consume dead animal matter, such as dead insects or larger animal carcasses.
Sounds like fumigation might be the answer.