Definitions

Weta

Weta

Weta are around 70 insect species endemic to the New Zealand archipelago. Weta are large by insect standards, some species among the largest and heaviest in the world. Their physical appearance is that of a cross between a cockroach and a cricket with the addition of large legs. The name comes from the Māori language word 'wētā'.

General characteristics

By virtue of their ability to cope with variations in temperature, weta can be found in a variety of environments including alpine, forests, grasslands, caves, shrub lands and urban gardens. They are nocturnal and flightless. Different species have different diets. Most weta eat other invertebrates but one group of weta endemic to New Zealand (the tree and giant weta) have evolved to eat mostly leaves, flowers 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 are known to arc their hind legs into the air in warning to foes. The female weta looks like she has a stinger, but it is really an ovipositor which enables her to lay eggs inside rotting wood

New Zealand had no native land mammals apart from native bats for millions of years before humans arrived. Ecological niches that were filled by mammals in other parts of the world were filled by native fauna in New Zealand. It has been suggested that the weta’s place in the ecosystem is comparable to that held by mice and other rodents elsewhere in the world. For example, like their foreign mouse equivalents, they are hunted by an owl: in this case the Morepork, New Zealand’s only surviving native owl. Weta also pass seeds of some plant species through their digestive tracts unharmed, thus acting as seed dispersers. It is yet to be seen how decreases in weta populations are affecting native plant species that rely on the weta's help.

Taxonomy and evolution

Weta may have survived virtually unchanged since the Mesozoic era, although there is no fossil evidence of this. In this respect, they can be compared with the tuatara. Fossilized orthoptera have been found in Australia, and weta there are called King Crickets. Some people think that weta were present in ancient Gondwanaland before New Zealand separated from it although it is also possible they dispersed as they must have done so to colonise New Caledonia and the Chatham Islands.

Giant, tree, ground, and tusked weta are all members of the family Anostostomatidae (traditionally in the Stenopelmatidae, but recently separated). Cave weta are members of the family Rhaphidophoridae called cave crickets or camel crickets elsewhere], in a different Ensiferan superfamily.

Giant weta

There are 11 species of giant weta (Deinacrida spp.), most of which are significantly larger than other weta, despite already being large by insect standards. They are heavy insects with a body length of up to 10cm (4in) not inclusive of its lengthy legs and antennae, and weigh about 20-30g. A captive giant weta (Deinacrida heteracantha) filled with eggs reached a record 70g, 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.

Tree weta

Tree weta (Hemideina) are those most commonly encountered in suburban settings. They are up to 40 mm long and most commonly live in holes in trees formed by beetle larvae. A large hole, called a gallery, might house up to ten females and one male. Tree weta are nocturnal. Their diet consists of plants and small insects. The males, which have much larger jaws than the females, hiss and bite when threatened.

There are seven species of tree weta:

  • The Auckland tree weta Hemideina thoracica (also called tokoriro) can be found throughout the North Island apart from the Wellington-Wairarapa region.
  • The Wellington tree weta H. crassidens occupies Wellington, the Wairarapa, the northern parts of South Island, and the West Coast.
  • H. trewicki in Hawke's Bay.
  • H. femorata in Canterbury.
  • A rare H. ricta species in Banks Peninsula.
  • The West Coast bush weta H. broughi largely overlaps with the Wellington tree weta on the West Coast.
  • H. maori, the mountain stone weta, lives in the drier areas of the central South Island High Country. At most sites it lives on the ground, under stones or in crevices but in at least two sites which have not be modified greatly it happily lives both in trees and on the ground

Mountain stone weta can survive being frozen for months at a time in a state of suspended animation down to temperatures of -10°C. This is because their haemolymph (the insect equivalent of blood) contains special proteins which prevent ice from forming in their cells.

When the territories of species overlap, they may interbreed, although offspring are sterile.

Tusked weta

Tusked weta are distinctive because of the males having 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, the Middle Island tusked weta Motuweta isolata, and a newly-discovered species called the 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 only 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 and a Department of Conservation breeding program is establishing new colonies on other islands of the Mercury Island group. The Raukumara was discovered even more recently, in 1996, in the Raukumara Range near the Bay of Plenty. There are probably more species still to be identified.

Ground weta

Ground weta are classified in the genus Hemiandrus There are about 40 species of ground weta in New Zealand and another seven in Australia. Most of the Hemiandrus have not been described. They hide in burrows in the ground during the day and conceal the exit hole with a door. During the night ground weta hunt invertebrate prey and eat fruit.

Cave weta

The sixty species of cave weta have extra-long antennae, longer legs, a passive demeanour and deafness. Cave weta may be active within the confines of their caves during the daytime. They are classified as being in genera in Subfamily Ceuthophilinae of family Rhaphidophoridae, thus making them distant cousins of the other types of weta.

Conservation

Although the weta had native predators in the form of birds, 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 that 16 of the 70 species of weta are now at risk. Programmes to prevent extinctions have been implemented since the 1970s.

Cultural references

Footnotes

References

  • Johns, P. M. (1997). "The Gondwanaland weta: family Anostostomatidae (formerly in Stenopelmatidae, Henicidae or Mimnermidae): nomenclatural problems, world checklist, new genera and species". Journal of Orthoptera Research 6: 125-138.
  • Steve Trewick; Mary Morgan-Richards New Zealand Invertebrate Speciation. Retrieved on 2006-05-08..
  • Greg H Sherley Threatened Weta Recovery Plan. Department of Conservation. Retrieved on 2007-11-07..

External links

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