Tree wetas (Hemideina crassicruris) (Orthoptera: Stenopelmatidae) of Stephens Island, Cook Strait

Abstract

Tree wetas (Hemideina crassicruris) were studied in kohekohe (Dysoxylum spectabile) forest on Stephens Island, Cook Strait, between 5 and 17 January 1978. Mark and recapture observations suggested a population density of at least 5300 wetas ha⁻¹ and a biomass of 42 kg ha⁻¹. Activity of wetas increased with temperature and humidity. Tuataras are important predators on Stephens Island and probably deter wetas from moving onto the forest floor. The enlarged head and jaws of male wetas are associated with head-on fights for occupancy of galleries. Single, adult males occupy galleries with a harem of up to 9 females. Stridulation was associated with agonistic encounters and was most frequent shortly before dawn. Seventeen percent of males and 42% of females were damaged. Moulting, copulation, and oviposition were observed, and females carried up to 96 mature eggs. Stephens Island tree wetas reach larger sizes overall, and males have relatively larger heads, than in other populations of the Cook Strait region. The number and size of galleries and the presence or absence of predators may be important determinants of weta population density, sex ratio, harem formation, and activity on the ground.