Tree Weta (Hemideina) Ecology
There are 7 species within the genus Hemideina (tree weta). Because many tree weta species are common and widespread they have been used extensively in studies of ecology and evolution. Tree weta are common in forests and suburban gardens throughout most of New Zealand. They are arboreal nocturnal orthoptera that hide in hollow tree branches during the day and feed on leaves, flowers, fruit and insects at night.
We now know that tree weta are not much like mice (Griffin et al. 2011). Although weta are nocturnal and produce large poos (frass), they are much slower than mice and have quite a different impact on the forests in which they live. Weta have a slower rate of reproduction than mice and as cold blooded animals (ectotherms) they have a much lower metabolic rate. Thus weta eat less and grow more slowly than small mammals can. Tree weta mostly eat leaves (Wehi & Hicks 2010) rather than the mouse diet of seeds and insects, although tree weta do scavenge dead invertebrates and eat some fruit and seeds. Some tree seeds pass through weta intact and can germinate (Duthie et al. 2006), but the majority of seeds eaten by weta are digested (Wyman et al 2010).
Tree weta hide in holes in hollow tree branches during the day where they are safe from birds and mammals than might like to eat them. Many native birds eat weta (e.g. kiwi, robin, tomtit, ruru) and many introduced mammals also like weta for lunch (e.g. hedgehogs, stoats, possums, mice, rats, cats). During the day while the weta hide in refuge holes (roosts) they are safe, but at night they have to come out to feed. When attacked tree weta raise their spiny back legs above their bodies, looking large and prickly, to try and escape being eaten. When the weta brings its legs down again, the inside of their femur, where there are many small pegs, rubs against the stridulatory ridges on their abdomen. This rubbing of pegs on ridges makes a loud rasping or scratching sound as a defence. Tree weta also stridulate to each other at night by moving their abdomen up and down across the femora pegs (Field & Jarman 2001).
Weta adults like to live together in the summer and autumn but not during the winter (Wehi et al 2012). During the summer 10 or 12 adult tree weta can be found squeezed together into the same refuge hole. Usually there is just one or two male tree weta with many females (the harem). Males have elongated mandibles that they use in combat with other males over access to large tree holes where many adult females hide together during the day. In Hemideina maori the male weta with the largest heads are found hiding together with the largest harems, so it is thought these large-jawed males have won fights for the right to mate with many females (Gwynne & Jamison 1998). In H. crassidens large-jawed males also win fights and mate with many females (Kelly 2006).
Female tree weta lay their eggs into the soil by inserting their ovipositer into the ground. The eggs hatch about 8 months later and the nymphs look like tiny versions of their parents.
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Wyman TE, Trewick SA, Morgan-Richards M, and Noble ADL. 2010. Mutualism or opportunism? Tree fuchsia (Fuchsia excorticata) and tree weta (Hemideina) interactions. Austral Ecology. DOI: 10.1111/j.1442-9993.2010.02146.x.