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|Male Wellington tree weta|
|Male Wellington tree weta|
Weta (plural wetas or weta) is the common name for a group of about 70 insect species in the families Anostostomatidae and Rhaphidophoridae, endemic to New Zealand. The English word is borrowed from the Māori language, where singular and plural have the same form. The Maori-derived plural weta is standard in New Zealand, while the anglicized plural wetas is generally used elsewhere.
Many weta are large by insect standards and some species are among the largest and heaviest in the world able to fly. Their physical appearance is like a katydid, long-horned grasshopper, or cricket, but the hind legs are enlarged and usually very spiny. Many are wingless. Because they can cope with variations in temperature, weta are found in a variety of environments, including alpine, forests, grasslands, caves, shrub lands and urban gardens. They are nocturnal, and all New Zealand species are flightless. Different species have different diets. Most weta are predators or omnivores preying on other invertebrates, but the tree and giant weta eat mostly lichens, leaves, flowers, seed-heads and fruit.
Weta can bite with powerful mandibles. Tree weta bites are painful but not particularly common. Weta can inflict painful scratches, with the potential of infection, but their defence displays consist of looking large and spiky, and they will retreat if given a chance. Tree weta arc their hind legs into the air in warning to foes, and then strike downwards, so the spines could scratch the eyes of a predator. Pegs or ridges at the base of the abdomen are struck by a patch of fine pegs at the base (inner surface) of the legs and this action makes a distinctive sound. These actions are also used in defence of a gallery by competing males. The female weta looks as if she has a stinger, but it is an ovipositor, which enables her to lay eggs inside rotting wood or soil. Some species of Hemiandrus have very short ovipositors, related perhaps to their burrowing into soil and laying their eggs in a special chamber at the end of the burrow.
Fossilized orthopterans have been found in Russia, China, South Africa, Australia and New Zealand, but the relationships are very open to different interpretations. Certainly, most weta of both families are in the Southern Hemisphere lands. Weta were probably present in ancient Gondwanaland before Zealandia separated from it, although this does not explain their presence in New Zealand. It is very likely that weta dispersed to colonise New Caledonia and tokoriro. Rhaphidophoridae also dispersed over sea to colonize the Chatham Islands. Although they are of an ancient lineage, the present species are quite young, which conflicts with those earlier ideas about dispersal of weta forebears around the Southern Hemisphere (Wallis et al. 2000).
Giant, tree, ground, and tusked weta are all members of the family Anostostomatidae (formerly in the Stenopelmatidae, but recently separated (Johns, 1997)). Cave weta are better called tokoriro, and are members of the family Rhaphidophoridae called cave crickets or camel crickets elsewhere, in a different ensiferan superfamily.
Tree weta eggs are laid over the autumn and winter months and hatch the following spring. A tree weta takes between one and two years to reach adulthood, and over this time will have to shed its skin around ten times as it grows.
The 11 species of giant weta (Deinacrida spp.), most significantly larger than other weta, are themselves large by insect standards. They are heavy insects with a body length of up to 100 mm (4 in) excluding their lengthy legs and antennae, and weigh about 20–30 g. A captive giant weta (Deinacrida heteracantha) filled with eggs reached a record 70 g, making it one of the heaviest documented insects in the world  and heavier than a sparrow. The largest species of giant weta is the Little Barrier Island weta, also known as the wetapunga. Giant weta tend to be less social and more passive than other weta. They are classified in the genus Deinacrida, which is Greek for "terrible grasshopper". They are found primarily on small islands off the coast of the main islands, and are examples of island gigantism.
Tree weta (Hemideina) are those most commonly encountered in suburban settings in the North Island. They are up to 40 mm long and most commonly live in holes in trees formed by beetle and moth larvae or where rot has set in after a twig has broken off. The hole, called a gallery, is maintained by the weta and any growth of the bark surrounding the opening is chewed away. They readily occupy a preformed gallery in a piece of wood (a weta motel) and can be kept in a suburban garden as pets. A gallery might house a harem of up to 10 juveniles of both sexes, females and one male. Tree weta are nocturnal. Their diet consists of plants and small insects. The males have much larger jaws than the females, though both sexes will hiss and bite when threatened.
The seven species of tree weta are:
Mountain stone weta can survive being frozen for months in a state of suspended animation down to temperatures of -10°C, because their haemolymph (the insect equivalent of blood) contains special proteins that prevent ice from forming in their cells. It also displays the defensive behaviour of "playing dead", by lying still for a short time on its back with legs splayed and claws exposed and jaws wide open ready to scratch and bite.
When the territories of species overlap, as with the related species H. femorata and H. ricta on Banks Peninsula, they may interbreed, although offspring are sterile.
Tusked weta are distinctive because the males have long, curved tusks projecting forward from their jaws. The tusks are used to push an opponent; they are not used for biting. The females are similar to ground weta. Tusked weta are mainly carnivorous, eating worms and insects. They consist of three species: the Northland tusked weta Hemiandrus monstrosus, now named Anisoura nicobarica; the Middle Island tusked weta Motuweta isolata; and a newly discovered Raukumara tusked weta, Motuweta riparia. The Northland tusked weta lives in tree holes similar to tree weta. The Middle Island tusked weta, also called the Mercury Island tusked weta after the islands on which it lives, was discovered in 1970. It is a ground-dwelling weta, covering its shallow burrows with leaves. The Middle Island weta is the most endangered weta species, so a Department of Conservation breeding programme is establishing new colonies on other islands of the Mercury Island group. The Raukumara was discovered in 1996, in the Raukumara Range near the Bay of Plenty. Probably, more species are still to be identified.
Ground weta are classified in the genus Hemiandrus. About 40 species of ground weta occur in New Zealand, and several very similar ones are found in Australia. They are also very like the Californian Cnemotettix—a similarity perhaps due to their very similar habits and habitat. Most of the Hemiandrus have not been described. They hide in burrows in the ground during the day, and those that live in open ground (e.g., H. focalis) conceal their exit holes with a specially made perforated door. During the night, ground weta hunt invertebrate prey and eat fruit.
The 60 species of cave weta have extra-long antennae, and may have long, slender legs and a passive demeanour. Although they have no hearing organs on their front legs like species of Hemideina and Deinacrida, some (e.g., Talitropsis spp.) are very sensitive to ground vibrations sensed through pads on their feet. Specialised hairs on the cerci and organs on the antennae are also sensitive to low-frequency vibrations in the air. Cave weta may be active within the confines of their caves during the daytime, and those individuals close to cave entrances venture outside at night. But most species are forest dwellers and a few are to be found in the high alpine screes living among the broken rocks covered with snow up to six months of the year. The weta stay frozen until spring time. New Zealand species are classified in several genera in subfamily Macropathinae of family Rhaphidophoridae, and are very distant cousins of the other types of weta.
Although the weta had native predators in the form of birds (especially the weka and kiwi), reptiles, and bats before the arrival of humans, introduced species such as cats, hedgehogs, rats (including kiore) and mustelids have caused a sharp increase in the rate of predation. They are also vulnerable to habitat destruction caused by humans and modification of their habitat caused by introduced browsers. New Zealand’s Department of Conservation considers 16 of the 70 species at risk. Programmes to prevent extinctions have been implemented since the 1970s.
Some examples of especially endangered species are even tracked by radio beacons.