Wētā is the Māori name for a group of large, spiny, wingless grasshopper-like insects. These giants of the insect world are normally found in dark, damp tunnels in hollow trees, rock cavities or soil, anywhere from sand dunes to above the snowline. Wētā are related to grasshoppers, locusts, crickets and katydids (all members of the order Orthoptera) and, like their relatives, have powerful hind legs for jumping.
New Zealand has over 100 different species of wētā in two families: the Anostostomatidae and the Rhaphidophoridae.
Anostostomatids are large-bodied wētā with heavy legs. There are four groups:
Rhaphiophorids are more athletic and have smaller bodies. They have very long, slender legs and can perform enormous leaps. They are commonly known as cave or jumping wētā.
Although these wētā species are found only in New Zealand, there are wētā-like insects in Australia, South Africa, South America, Europe, Asia and North America. Outside New Zealand, similar heavy-bodied, burrowing insects are known as king crickets. Light-weight jumping varieties are known as cave crickets or camel crickets.
The most common wētā are the seven species of tree wētā (genus Hemideina), found in gardens or in the bush in most regions of New Zealand (except lowland Otago and Southland).
Most adult tree wētā have bodies between 4 and 6 centimetres long. Tree wētā are predominantly herbivorous, feeding on leaves and fruit. They are seldom found alone, preferring instead to associate in groups, which often share space in tree tunnels.
By day the tightly packed gatherings are peaceful, but at night violence prevails. Male tree wētā have enlarged heads – up to twice the length of the female’s head – with oversize jaws for fighting. The larger individuals set themselves up in the best tunnels where they repel other males but accept females to accumulate a harem – five or more females where there is room. Males fight to remove lesser individuals when competing for tunnels. Fights are not to kill – although legs and antennae, or parts of them, may be lost in the process.
Tree wētā communicate by stridulation – pegs on their hind legs are scraped over comb-like ridges on the side of their body. This produces a chirping sound that they hear through ears on the sides of their front legs.
Tree wētā eggs are laid during autumn and winter, hatching in spring. The female wētā has a long, curved egg-laying spike (ovipositor), which can be bent under her body to force eggs down into the soil.
Like all insects, wētā need to shed their external covering (exoskeleton) periodically to grow. Once it has hatched from the egg, the tiny version of the adult must pass through at least 10 moults before it reaches adulthood. This process takes one to two years.
Once they reach adulthood, tree wētā survive for six to ten months in lowland situations, but in an alpine habitat they may live for several years. New Zealand alpine wētā (Hemideina maori) are by far the largest insects that can freeze solid in winter and thaw out and crawl away in spring. Most cold-tolerant insects have antifreeze (glycol) in their fluids. But these wētā can freeze because their tissues are not damaged when ice crystals form.
Giant wētā (genus Deinacrida) are predominantly herbivorous. They are not as social as tree wētā and tend to occupy temporary, poorly protected shelters by day, which exposes them to predators.
Giant wētā did not survive long in lowland areas after the arrival of humans and rats in New Zealand. Of the 11 giant wētā species, only six still occur on mainland New Zealand – in the South Island mountains, above the level where rats live. The other species now survive only on offshore islands.
The most impressive wētā is the wētāpunga (Deinacrida heteracantha), a species of giant wētā now confined to Little Barrier Island. Females reach a body length of 7.5 centimetres, and their hind legs are 13 centimetres if stretched out. Like other lowland giant wētā species, these giants of the insect world were extinct on mainland New Zealand by 1900, killed by rats.
Lawyer and naturalist Walter Buller was enthralled by the giant wētāpunga. On one occasion in the 1860s, he captured a pair in woods near the Northern Wairoa River, tying them in a knotted handkerchief which he left to pick up later. At the end of the day the wētā had gone – they had chewed their way to freedom.
The ground wētā group (genus Hemiandrus) are not as well known or studied as much as other wētā. About 30 species occur throughout New Zealand. They lack the heavily spined hind legs of the tree wētā and live in burrows in the soil, reversing into the hole so they can face any enemies head-on. These active, carnivorous wētā emerge at night to climb vegetation and hunt for insect prey. Some larger species (with bodies at least 4 centimetres in length) occur in mountain regions.
Unlike other wētā species, ground wētā do not form social groups or stridulate (chirp by rubbing body parts together).
The females of some species are known to make a special brood chamber in their burrow and care for their eggs until after they have hatched.
Mature tusked wētā males have impressive tusks for fighting. Three species occur in northern New Zealand:
The cave wētā group is the most diverse. There are over 50 species ranging from small bush wētā only a few centimetres long to some Gymnoplectron species that have leg spans of up to 40 centimetres (with bodies only about 2.5 centimetres long).
They can be distinguished from other types of wētā by their antennae, which virtually touch in the middle of the head, and by their feet, which lack gripping pads. Cave wētā do not form harems like tree wētā, but they often gather (sometimes in large numbers if there is space) in dark, damp shelters by day. At night they forage in the bush, feeding on lichens, fungi and dead organic matter, including seabird carcasses.
Gibbs, George. New Zealand weta. Auckland: Reed, 1998.
Gibbs, George. The weta. Auckland: Reed, 2003.