Morphometric change, distribution, and habitat use of Cook Strait giant weta (Deinacrida rugosa: Orthoptera: Anastostomatidae) after translocation to Matiu-Somes Island

Abstract

Giant weta (Orthoptera: Anostostomatidae) are large flightless New Zealand insects in the genus Deinacrida. They usually survive in the absence of introduced rats and many have now been transferred to islands and areas after rodent eradications. One such transfer of the Cook Strait giant weta, D. rugosa was made from Mana Island to Matiu-Somes Island in 1996 and we investigated the sex ratio, morphometrics, growth, distribution, habitat use, nocturnal activity pattern and incidence of natural injury in February, May, September and December 2007 and February 2008. Most weta found were adults (82%), more adult females (74%) were seen than males but more male juveniles (61%) were seen than females. Weta from Matiu-Somes Island had slightly longer metatibiae than those from Mana Island. Cohorts of different-sized insects become larger in most successive samples indicating a 2-year development period following eclosion. Adults were always present but were most frequently seen in February when the smallest juveniles were also found, and large juveniles were common in September and December. Weta have spread throughout the island but were abundant over the northern half of the island with few found at the southern end. Adults and large juveniles were usually found on or near the ground whereas small juveniles were above ground on vegetation. Most adult weta were seen during the fi rst two hours of darkness in February on the ground or on short grass, and only five were on bushes. Overall, 22% of adults were injured, usually with damaged antennae or legs. Cook Strait giant weta are now so well established on Matiu-Somes Island that we consider this translocation a success.