Tuesday, January 4, 2011
The weta is one of NZ’s most infamous creatures. The Maori called them Devils of the Night, or Gods of Ugly Things. An early scientist, Sir Walter Buller, once attempted to collect and kill some wetas for studying. One was held underwater for four days but survived; another was still alive after being dropped into near-boiling water; while yet another ate its way out of his handkerchief. But in spite of their fearsome appearance they are quite harmless, and very rarely aggressive.
Wetas are found in several Southern Hemisphere countries apart from NZ. The largest species found here are the heaviest insects in the world, weighing up to 70g- however there are over 70 species of weta in NZ. Even older than the tuatara, wetas are a very primitive creature. Our wetas have changed very little since NZ was isolated from the rest of the world many years ago. In fact some species are very similar now to when they lived with the dinosaurs.
Wetas can be divided into four major groups - cave wetas, tree wetas, ground wetas, and giant wetas.
Cave Wetas can be identified by their small bodies with relatively long legs. One species in Northland has a body length of about 2.5 cm - but its total length from antennae to hind legs is 35cm. They choose to live in dark places- not just in caves but in crevices and mine tunnels, and under logs and houses. Deep in caves, there is not always a good food supply, so they are seldom found far from entrances.
Because they live in little or no light, they have very small eyes- so their long legs and antennae are needed to help them feel around in the dark. The antennae are also waved around in the air to detect air currents. If disturbed, they can move very quickly and can jump up to 2m.
Cave wetas occasionally eat each other before their shells get hard, but usually they just eat soft plants like algae, as well as fungi and dead animals. On dark moonless nights, they often come outside in large groups to feed.
Tree and Ground Wetas: Tree wetas (or bush wetas) are NZ’s most common weta, found everywhere except in the far south. They are often unearthed hiding in piles of firewood, and are distinguished by their large heads. Like grasshoppers they have ears on their front legs, while the back legs are rubbed against their stomach to produce mating and fighting noises. Fighting is common amongst males competing for a group of females- the winner is usually the weta with the biggest jaws.
Tree wetas eat the leaves of many different plants, but prefer the softer leaves of some species such as mahoe or karamu. The females will sometimes eat their own discarded skins or other dead insects, to get extra energy for egg laying.
Ground wetas are much smaller than tree wetas and don’t have such big heads. As the name suggests they live in the ground, often in holes left by other insects, such as grass grubs and cicadas. Ground wetas, like cave wetas, are silent and have no ears.
Giant Wetas are the least common, but most fascinating type of weta found in NZ. Ten species have been discovered so far, in a variety of habitats - some live in burrows, some in the tops of trees, and some on alpine rock slopes. Most species are found in only very small areas, such as the Mahoenui giant weta - found only in a 300 hectare area of gorse in the King Country.
They are too large to jump (some are up to 8cm long), and are quite slow moving. This makes them readily preyed upon by rats, more so because the burrows of some species are large enough for a rat to enter. Because of this, and their limited distribution, most species are in danger of becoming extinct. Many of the largest species are now found only on offshore islands where rats have been eliminated. All our species of giant weta are protected by law.
The various types of wetas lay their eggs in various ways, because of their diverse habitats. Female cave wetas use their ovipositor (an egg laying organ extending form the rear end) to find soft cave mud of the right texture and depth, then lay just one or two eggs per hole. Tree wetas lay roughly 250 eggs in the soil (about 15mm down) near the base of their tree- the only time in their life that they descend to the ground.
Ground wetas lay their eggs in the burrow walls, where the young wetas end up spending much of their early life; giant wetas lay up to 400 eggs when they reach their maximum size (just before dying), usually in soil near their natural habitat.
Most wetas live for around two years, during which they evolve form an egg to a series of immature forms known as nymphs, in instars, and finally to full adult maturity. However, the details of the life cycle are poorly known for many species. Cave wetas lay their eggs in late autumn. The eggs take about 8 months to incubate, after which the nymph goes through three moults (each moult is an instar) before reaching maturity. A typical ground or tree weta goes through 10 instars. Each stage is only slightly different from that before it, so that by the time the weta reaches the sixth or seventh instar it is almost mature. Giant wetas also go through about ten instars. The often break their antennae while shedding skin between instars, but can easily regenerate them.
Posted by FireCat14