Why are some weta (Orthoptera: Stenopelmatidae) vulnerable yet others are common?

Abstract

The large (4 g) to very large (40 g) stenopelmatid orthopterans of New Zealand are known collectively as weta. A consideration of 20 species of Hemideina, Deinacrida and tusked weta reveals that at one end of a vulnerability gradient are those species which thrive in the presence of key predators (rats), while at the other end are species that have become extinct on the mainland but still survive on predator-free island refuges. Habitat modification does not appear to be a factor in these extinctions. This paper reviews the lifestyles and some important biotic parameters that seem to determine their relative vulnerability along this gradient. When predators are present, the factors leading to extinction are large body size, use of temporary refuges, protective quality of the refuges, time spent on the ground and the effectiveness of their defensive behaviour.