Deinacrida tibiospina

As one of the smallest known species of giant wētā, Deinacrida tibiospina grows to only around 30-40mm long, and weigh just 7 grams.[1][2][4] Like many other giant wētā, such as Deinacrida rugosa, the overlapping armoured plates on their back are wrinkled.[5] Adults of the species can be varying shades of brown, sometimes with a reddish hue.[3] Their bodies have a compressed appearance and dense spines on the upper side of their hind femurs.[3] As with almost all wētā, D. tibiospina are wingless.[6]

There is sexual dimorphism in this species.[7] Female D. tibiospina are larger than males, a common trait in many Orthoptera.[7][8][6] Males of the species also have fewer hind femoral spines than females.[7]

Deinacrida tibiospina live in alpine areas of Kahurangi National Park, located at the North-Western corner of New Zealand's South Island.[2] The wētā dwell above the tree line in sub-alpine tussock and herbfield zones of mountains,[9] observed at altitudes between 900 and 1500 meters.[1][7] Populations of D. tibiospina occur at very low densities at scattered localities within the central and eastern areas of what was North-West Nelson Forest Park.[3]

Throughout the day, Deinacrida tibiospina often shelter at the base of tussocks, Astelia, flax and other alpine plants.[3][7][9] Their lifespan may be 2–3 years as wild populations have been observed with 3 distinct age classes in February and March.[3][4] Like other wētā, D. tibiospina are nocturnal,[3] but they may be comparatively inactive because of the cold temperatures in their alpine habitat.[1]

Little research has been completed on the diet of D. tibiospina but they do not seem to like peanut butter, used as a lure for monitoring methods, as much as other wētā.[1]

Deinacrida tibiospina was first described in 1950 by New Zealand scientist John Salmon.[6] The species name tibiospina translates to tibia spine, or shin spine. This is likely a reference to the species' densely spined hind legs.[2][3] Why the species is not called femoraspina because most of its spines are on the femurs, not the tibia, is a mystery.[2]

Current phylogenetic and systematic research suggests Deinacrida tibiospina is a sister species of the lowland species D. carinata.[10][11]

The low density of Deinacrida tibiospina may be natural or it could be a result of human impacts.[1] If the latter is true, human-introduced mammalian predators such as rodents may threaten D. tibiospina populations, as other giant wētā species have been significantly impacted where these predators exist.[2] It is not certain, though, if D. tibiospina are as at risk to mammalian predation as rodents may not be abundant at high elevation.[2][12] A 2010 study using footprint tracking tunnels found that mouse populations did overlap D. tibiospina habitat, however, wētā density was the highest at locations with the fewest mouse observations.[1] These findings may imply that D. tibiospina are indeed negatively impacted by mice.[1]

In comparison with its close relatives, Deinacrida tibiospina has not received a great amount of conservation work. In 1989, a Department of Conservation report listed Deinacrida tibiospina as needing urgent research to prevent extinction,[12] but by 1998 the Department of Conservation Threatened Weta Recovery Plan listed D. tibiospina as low priority for conservation management.[2]

A University of Otago study found tracking tunnels were not reliable for monitoring the species because their scarcity and lack of attraction to peanut butter lures results in low counts.[1] One generation of Deinacrida tibiospina has, however, been successfully bred in captivity, generating hope for conservation efforts should the species need them.[2][3]