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Tree Weta  Tree weta (Hemideina). This adult male weta is performing its best defence display with raised hind legs and mandibles agape. Weta can communicate with each other with a rasping sound made by rubbing pegs on the inside of their hind legs across a row of ridges on their abdomen (stridulating). It is thought that males are territorial and that they stridulate at night to let other males know where they are and to call females to them. All tree weta find holes to hide in during the day, the holes are usually in tree branches and are formed by beetle larva. Adult female tree weta will share a hole in a tree trunk or tree branch if the space is large enough. A male that owns a large tree hole (or gallery) can mate with the females inside and so males fight for access to the best galleries. Male tree weta have much longer and wider jaws than the females do. Females have a long curved ovipositor, which they use to lay eggs straight into the ground. The eggs hatch about eight months after laying and the little weta look just like the adults, only smaller. In most places within New Zealand just a single species of tree weta is found but where two species overlap they often share galleries. This leads to mating between species and we have been studying hybridisation between species and between chromosome races of the same species. For example on Bank Peninsula the two species H. femorata (the Canterbury tree weta) and H. ricta (the rare Banks Peninsula tree weta) meet and a few hybrids are produced. These hybrids are infertile so there is no gene flow between this pair of species. Also visit Tree Weta Genetics page.
References: Wellington Weta  The Wellington weta (Hemideina crassidens) is found in the lower North Island and down the west coast of the South Island. A similar species is found in Hawkes Bay (H. trewicki). The Hawkes Bay species looks similar to the Wellington tree weta except the latter usually has a dark pronotum (the shield shaped structure directly behind the head) whereas the Hawkes Bay tree weta usually has a pale pronotum with striking black lines. These two species were recognised on the base of genetic differences, including differences numbers of chromosomes. The Wellington weta has two chromosome races. The race in the North Island and in the north of the South Island has 15 (XO) chromosomes in the males and 16 (XX) chromosomes in the females. South of the Buller River this species has 19 (XO) chromosomes in the male and 20 (XX) in the female. By studying the chromosomes of hybrids produced from a cross between these two races we know that the difference in chromosome number is due to a simple break of two chromosome pairs at their centromere. A subspecies of the Wellington weta (H. crassidens crassicruruis) is found only on Stephens Island, the Cooks Strait. The weta in this population are darker and have thicker legs than Wellington tree weta from the mainland.
References: Auckland Tree Weta  Auckland tree weta (Hemideina thoracica). This species comprises at least eight chromosome races with parapatric ranges throughout central and northern North Island, New Zealand. Members of the chromosome races look the same on the outside so to study them one must look at mitotic cells and count their chromosomes. In Northland there are many chromosome races and it is thought these races evolved while populations were isolated on islands during the Pliocene. The races are now in contact with one another but small disadvantage suffered by the hybrids appears to be maintaining the chromosome races as distinct.
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