T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Weta (Mercury Islands tusked wētā) Motuweta isolate

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Orthoptera
Suborder: Ensifera
Family: Anostostomatidae
Genus: Motuweta
Species: M. isolata
Binomial name: Motuweta isolate
Common name: Mercury Islands tusked wētā, , Middle Island tusked wētā

Motuweta isolate is a large flightless rare insect, discovered in 1970 living on a single small island, the 13-hectare Middle Island in the Mercury Islands, northern New Zealand where the population was estimated at fewer than 200 individuals. Although it may have once lived on the New Zealand mainland and several other islands in the Mercury island group, it is believed that invasive rats may have wiped the Motuweta isolate out in all but one location. 
Motuweta isolata is the largest of three known species of tusked weta in New Zealand, 90 mm long. Captive males can weigh 28 g and females 37 g, though wild specimens are generally smaller: 23 and 25 g. Adult males are distinguished by long brown tusks curving from their mandibles, projecting far in front of their head; these vary significantly in size between males. They use these to spar with other males in territorial pushing contests, each trying to overturn the other. If disturbed, they will raise their forelegs, hiss, and gnash their jaws; they stridulate by rubbing their femurs against their abdomen, and males can make a rasping noise by rubbing their tusks together. Both sexes will also defecate foul smelling liquid faeces. Despite these displays, they rarely bite when handled.

They are nocturnal usually remaining in underground chambers and only emerge to feed on other invertebrates on the darkest nights, when there is no moon and it is calm, warm and damp. They dig an underground chamber, plaster and smooth the walls with saliva, back in, and seal the entrance with a plug made of soil and saliva. They are reluctant to emerge, coming out during the darkest nights when it is warm and moist and there is little moonlight. This seems to be a strategy for avoiding tuatara and the numerous lizards on the forest floor.

Eggs are laid in the soil and take anywhere from three to nine months to hatch. From hatching to adulthood takes 16–17 months, and adults live for 6–10 months after their final moult.

Motuweta isolate have been saved from extinction by a captive breeding programme and translocation. It the most endangered wētā and is ranked Nationally Critical by the Department of Conservation. Between 2000 and 2003, 67 Middle Island tusked weta were released on Red Mercury Island and 80 on Double Island.
In 2005 surveys located 11 wetas on Red Mercury and 4 on Double Island. Juvenile wetas were found on both islands during the surveys, showing that successful breeding had occurred.