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Underwater Weta

Bernard Carpinter

Tusked weta that can walk underwater are the latest species of weta to come under study by the research team headed by Dr George Gibbs of the School of Biological Sciences.

The team, recognised leaders in their field, were alerted when Department of Conservation field staff discovered an unusual weta in a remote corner of the Raukumara Forest Park east of Opotiki in 1995. Gibbs received the original specimen for identification and immediately recognised it as a highly significant find.

Further investigation led to the startling discovery that this new weta is almost aquatic in its choice of habitat. They are found, along with the rare native Hochstetter's frog, under stones beside small streams. At night they move about on the stream banks and foliage of riparian shrubs.

Their streamside location is unusual for a weta and may be a reason for their survival. When disturbed they jump or roll into the stream and are able to crawl about under water and survive there for at least five minutes, probably considerably longer, thus escaping the predator and washing off their strong scent.

Before this discovery, only two native species of tusked weta were known, a tiny one in the Hokianga region of Northland and a gigantic one from a small island in the Mercury Group, off Coromandel Peninsula. Thanks to some genetic studies, initiated by Victoria researchers, the tusked weta are now being recognised as a distinct grouping of weta, not closely related to other kinds of weta. The tusked group are found also in Australia and southern Africa, suggesting they predate the splitting of Gondwanaland.

A survey team of DoC officers and three biologists from Victoria's School of Biological Sciences searched the remote Motu catchment area in April last year, after flying in by helicopter. They found over 100 of the new weta.

"The species is surviving remarkably well in rat, possum, cat and pig infested terrain," Gibbs says. "It appears they use the stream as a means of survival, hiding under water for long lengths of time to avoid predators. They are also more athletic than tree wetas; their ability to jump makes it easier to escape. They also appear to have a more flexible life cycle than their island equivalents.

"It's great to find this tenacious species. The small Northland tusked weta is not surviving very well and the oversized Mercury Island species leads a very precarious existence. Attempts to breed it in captivity have been fraught with problems to date. If a rat were to get onto the island it would quickly become extinct," Gibbs says. It may be possible to use this mainland species to learn how to maintain captive colonies of the other more endangered tusked weta.

The tusks on this new weta are quite small, much less impressive than the other two tusked weta species. They develop only on the mature males. Tusks are used for male-male fighting bouts in which they protect their ownership of refuges.

Bernard Carpinter is a journalist at Victoria University.