Weta

Weta
Male Wellington tree weta
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Orthoptera
Suborder: Ensifera
Superfamily: Stenopelmatoidea, Rhaphidophoroidea
Family: Anostostomatidae, Rhaphidophoridae

Weta is the name given to about 70 insect species endemic to New Zealand. There are many similar species around the world, though most are in the southern hemisphere. The name comes from the Māori word 'wētā' and is the same in the plural (like 'sheep'). The Māori word for the Giant Weta is 'wētā punga' (lumpy or jointed weta), sometimes rendered in English as 'god of ugly things'.

Contents

General characteristics

Many weta are large by insect standards and some species are among the largest and heaviest in the world. Their physical appearance is like a katydid or long-horned grasshopper or a 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.

Defensive male Wellington tree weta

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 that 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[1] 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.

New Zealand had no land mammals (apart from native bats) before humans arrived, and ecological niches occupied by mammals in other parts of the world were taken by non-mammals. The weta’s place in the ecosystem is comparable to that held by mice and other rodents elsewhere in the world. For example, they are hunted by an owl, the morepork, New Zealand’s only surviving native owl. Weta 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 may rely on the weta's help.

The weta's lifestyle and habitat, where it may choose to remain concealed in suburban environments until unexpectedly confronted, combined with its notoriously unfriendly appearance, make it a frequent victim of irrational human aggression.

Taxonomy and evolution

Tree weta climbing

Fossilized orthoptera 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. Pratt, Morgan-Richards and Trewick think that weta were present in ancient Gondwanaland before New Zealand separated from it[2] although it is also possible they dispersed as they must have done so to colonise New Caledonia and 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 members of the family Rhaphidophoridae called cave crickets or camel crickets elsewhere, in a different Ensiferan superfamily.

Giant weta

Poor Knights giant weta (Deinacrida fallai) - this specimen has an overall length of 200 mm (8 in)

There are 11 species of giant weta (Deinacrida spp.), most significantly larger than other weta, which are themselves large by insect standards. They are heavy insects with a body length of up to 100 mm (4 in) not inclusive of its 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 [3] 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

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 ten juveniles of both sexes, females and one male. Tree weta are nocturnal. Their diet consists of plants and small insects. The males, which usually have much larger jaws than the females, hiss and bite when threatened.

Female Wellington tree weta

There are seven species of tree weta:

Mountain stone weta can survive being frozen for months 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 that prevent ice from forming in their cells. It also has the 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

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, 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 and 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. 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 several very similar ones in Australia. There 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 the exit hole with a specially made perforated door. During the night ground weta hunt invertebrate prey and eat fruit.

Cave weta

The 60 species of cave weta have extra-long antennae, and may have long, slender legs, 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 rock that are covered with snow up to six months of the year. 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.

Face

Lower leg (tarsus)with two claws and sensory pads

Upper leg

Underside with parasites

Conservation

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 that 16 of the 70 species of weta are now at risk. Programmes to prevent extinctions have been implemented since the 1970s.

Some examples of especially endangered species are even tracked by radio beacons.[4]

Cultural references

Footnotes

  1. ↑ Kleinpaste, Ruud (1997). Scratching for a living. 
  2. ↑ Diversification of New Zealand weta (Orthoptera: Ensifera: Anostostomatidae) and their relationships in Australasia Philosophical Transactions of the Royal Society
  3. ↑ "Book of Insect Records". http://ufbir.ifas.ufl.edu/chap30.htm. 
  4. ↑ Eel's costly snack - The New Zealand Herald, Saturday 16 May 2009

References

External links