Hemideina crassidens, The Wellington Tree Weta

Order: Orthoptera     Family: Anostostomatidae

Weta comprises of about 70 species in the genus Hemideina native to New Zealand. These members of the family Anostostomatidae are renowned for being the heaviest insects in the world, with the largest recorded individual weighing in at 71 grams (Salmon). Weta have colonized a plethora of environments but the Wellington Tree Weta, as indicated by its common name, resides in trees in forested environments. Its distribution reaches southern parts of North Island, northern parts of South Island and the west coast of New Zealand (Johns).

Members of the species Hemideina crassidens are generalists, feeding on small insects, lichen and plant tissue. Weta are also nocturnal. The males live with their harem of females in holes in trees formed by where rot has set, where beetle or moth larvae have previously grown in or where a twig has broken off (Johns). This hole is called a gallery and it is maintained by the weta; any bark that grows around the opening of the gallery is chewed away. A gallery might house 10 juveniles of either sex, several females and one male (Gibbs).

Weta are katydid-like in appearance with large spines on their hind legs. They have dark stripes running the length of their abdomen and a darkly colored pronotum. Tree weta are typically 40 mm long and wingless. Females of the species have a distinctively long and thick ovipositor which is used to dig into rotting wood to lay her eggs (Salmon). After the young hatch they undergo hemimetabolous development, spending their entire lives in the trees.

Males of the species have characteristically huge mandibles which they use to protect themselves and their harem of females from predators and competing males. When threatened, males will open their large mandibles while raising their hind legs in the air to display the spines along them (as pictured below). Despite being so large and intimidating, weta are relatively docile. Confrontations between males are rarely lethal; one will usually give up and leave (Gibbs). When facing off against a predator, the weta will attempt to flee while performing its threat display. However, a bite from a male tree weta is strong enough to break human skin and draw blood (Salmon).

Weta’s evolutionary history is thought to have occurred exclusively in the southern hemisphere. They were probably present in ancient Gondwanaland before Zealandia separated from it, although this does not explain their presence in New Zealand (Trewick). Although they are of an ancient lineage, the Wellington Tree Weta and many other present species are quite young, which conflicts with those earlier ideas about dispersal of weta forebears around the Southern Hemisphere (Wehi).

The Wellington Tree Weta in particular does not have any special conservation status but 16 of the 70 species of weta in New Zealand are either endangered or at risk (Sherley). This has been the result of the alteration or destruction of their habitat in tandem with the introduction of urban pets (cats and dogs) which have acted as additional predators of weta.

Female Wellington Tree Weta
Female Wellington Tree Weta
Male Wellington Tree Weta
Male Wellington Tree Weta
Male Tree Weta performing threat display
Male Tree Weta performing threat display

 

Links

http://www.asktheexterminator.com/Crickets/Giant_Weta_printer.shtmlhttp://wetageta.massey.ac.nz/Text%20files/treeweta.html

http://www.sciencedump.com/content/new-zealand-giant-tree-weta

http://www.terrain.net.nz/friends-of-te-henui-group/local-insects/tree-weta.html

http://www.dailymail.co.uk/sciencetech/article-2068547/Weta-insect-Heaviest-world-weighs-3-times-mouse.html

References

  • New Zealand. Department of Conservation. Biodiversity Recovery Unit. Weta. NZ Department of Conservation, n.d. Web. 24 Nov. 2015.
  • 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 (Orthopterists’ Society) 6 (6): 125–138. Doi:10.2307/3503546. JSTOR 3503546
  • Greg H Sherley (1998).”Threatened Weta Recovery Plan” Department of Conservation. Retrieved 2007-11-07.
  • Salmon, J. T. (January 1956).“A Key to the Tree and Ground Wetas of New Zealand”Tuatara 6 (1).
  • Gibbs, George. “Story: Weta.” Wētā –. The Encyclopedia of New Zealand, 9 Nov. 2015. Web. 24 Nov. 2015.
  • Trewick, S. A. and Morgan Richards, M. 1995. On the distribution of tree weta in the North Island, New Zealand.Journal of the Royal Society of New Zealand, 25(4): 1-9.
  • Wehi, P.M. & Hicks B.J. 2010. Isotopic fractionation in a large herbivorous insect, the Auckland tree weta.Journal of Insect Physiology 56: 1877 – 18882.

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