The demon grasshoppers
What insects have the tusks of an elephant, can weigh as much as a thrush and yet live like mice? Only the New Zealand weta. As many as 100 species of these thorny creatures dwell in burrows , caves and crevices, from lush islands to snowy mountain crests.
Slogging through cold, wet beech forest at midnight is not my favourite pastime. Yet in January of this year, that’s what a group of us were doing: searching an old coal mine incline near Woolshed Creek, Canterbury, for a giant insect which had become something of a legend. Through the long night the flickering beams of our torches showed up plenty of wet leaves and dripping black trunks—but no weta. Patches of bush lawyer tore at our clothes. We tried a tussock area nearby, scanning the bare ground, looking under plants and probing crevices in the rock. At 1 A.M. we gave up, empty-handed.
Twenty-four hours later, our mood was one of elation. The Mount Somers weta had been rediscovered, alive and thriving, 37 years after the one-and-only previous specimen had been collected nearby.
The Mt Somers weta saga is more a detective story than an entomological one. It begins with a large, long-legged weta found in 1957 and passed on to the Entomology Division of the Department of Scientific and Industrial Research, Nelson. The brief inscription on the label read: “Mt Somers, 2000 ft. V. Hunt, 1957.” Within the inner circle of weta biologists it came to be referred to as the “Mt Somers weta” or simply the “mid-Canterbury weta”—if mentioned at all.
Fast-forward to 1991, and two biologists who are interested in the question of how many species of giant weta we have in New Zealand. Mary Richards, a doctoral student, and I begin investigating each of the known kinds and some unnamed ones as opportunities arise.
In November 1992, I borrow a number of giant weta specimens from the New Zealand Arthropod Collection at the Mt Albert Research Centre in Auckland. Among them is the Mt Somers weta. Although its colours are almost totally faded after years in alcohol, this sub-adult male proves to be very similar to a recently discovered mountain weta from the Kaikoura Ranges known as the “bluff weta.”
Armed with this information and the data label, we spend a day in January 1993 climbing the western slopes of Mt Somers, looking for the weta. The mountain yields little of help, but progress is made when a local resident identifies V. Hunt, the name on the label, as a former Canterbury deer stalker and tramper now living in England. On an impulse, I telephone him. His answer is all I could have hoped for. He clearly remembers the day and the exact spot where the weta was found. “In the beech forest near the tramway,” he says. He had picked it up because it looked remarkable: “black and red with maybe some white.” No ordinary weta, this one!
I become convinced that the Mt Somers weta will turn out to be identical with, or at least very similar to, the Kaikoura bluff weta, a species which hides in deep crevices by day—a vital clue, as it turns out.
In January 1994 I return to Mt Somers in the company of two Department of Conservation officers, a science technician and a rock-climber to look again for the elusive quarry. After our abortive Saturday night search in the forest, we decide to spend the next day looking for the weta on the cliffs—the sort of place the Kaikoura weta would inhabit. Tom Davies, our rock-climber, is in his element. Perched on a bluff high above the river, his excited yells tell us he has struck entomological pay dirt.
We follow him up, spread-eagling ourselves across the rocks. There it is, the unmistakable rear end of a large weta jammed deep into a 15 mm-wide crevice. We tickle it out gently with two slivers of manuka and hold in our hands the evidence that this giant weta is not extinct after all.
Seven more are seen during the next half hour. As we hang on to that cliff, we experience the thrill that Dr Orbell must have felt when he rediscovered the takahe in the Murchison Mountains in 1948.
The mt somers weta belongs to a group of insects known as giant weta—Deinacridaliterally the demon grasshoppers. Some of them are New Zealand’s largest insects. These monsters have survived here some 70 million years, in much the same form as they are today. They have watched the demise of the dinosaurs and the rise of the birds to dominance in primeval Aotearoa. Now they are under threat.
Finding new insects this size, or, in our case, re-finding one that was presumed extinct, is exciting stuff in 1994, although discoveries of this magnitude must have been almost commonplace to the early naturalists and explorers. Long before them, of course, the Maori were aware of these insects, and incorporated them into their knowledge system, calling the gigantic northern ones wetapunga, punga being the deity presiding over ugly things. The shortened version gives us the common name used in New Zealand for all these large night insects. On the West Coast, weta were referred to as taipo, “devils of the night.” The tree weta we now call by the uninspired pakeha name “Auckland weta” were referred to as putangatanga or tokoriro weta.
The Reverend William Colenso, best known for his discovery of many of New Zealand’s plants, was probably the first to secure a specimen of our largest weta. He collected one in 1839 at Paihia in the Bay of Islands and preserved it in a glass jar of alcohol.
It was not until 42 years later that he peered into the jar (he couldn’t get the lid off) and officially described it. However, the name he gave it was invalid, because the same insect had been described in 1842 by a Mr Adam White of the British Museum as Deinacrida heteracantha. The specimen seen by Mr White also came from the Bay of Islands, taken during the voyage of the Erebus and Terror in the spring of 1841.
These gigantic insects (reaching the weight of a song thrush), attracted much attention and comment. Considering their awesome size and presence in the Bay of Islands in those days (now they are confined to Little Barrier Island), one wonders why Captain Cook’s naturalists did not come across them much earlier.
Knowledge of our weta species built up steadily over the next century, and in 1950 a review by John Salmon indicated that we had six species of giant weta and possibly eight species of tree weta, as well as a number of smaller ground weta and many of the jumping cave weta types.
However, the excitement of discovery did not end in 1950. At least four more of the secretive nocturnal giant weta were to be revealed, including one of the most extraordinary insects in our fauna.
The first recent surprise came in 1962 when a small colony of giant weta were found in two patches of gorse on a farm near Te Kuiti. This was long after scientists had assumed that giant weta had become extinct on the North Island. Referred to as the Mahoenui weta (but lacking a scientific name), this species, which was probably once widespread in tawa forests, owes its existence to the protection of gorse spines. While it doesn’t seem particularly fond of gorse as food (it does eat the flowers, though) its thorny habitat has probably kept the rats at bay.
The second surprise came in 1970 when a party of herpetologists found a large weta on a tiny island in the Mercury Group, off the east coast of the Coromandel Peninsula. This creature was no ordinary giant weta because the jaws of the male carried elongate curved tusks projecting in front of the head. This elephant among weta is one of the most remarkable insect discoveries of the century.
For the third recent discovery we go to the mountains of the South Island in 1988 when Tony Whitaker, finder of the Mercury Island tusked weta, was exploring the Kaikouras, looking for records of a black-eyed alpine gecko which he had discovered a few years earlier. This gecko, which hides in rock crevices high in the mountains by day, was found to be sharing its habitat with a spectacular new grey weta with orange legs. As it happened, Tony’s handsome new insect matched a sun-bleached weta skeleton which had been found in 1953 but had languished in the Museum of New Zealand virtually unexamined ever since.
Our part in the quest for new weta had begun during Easter 1992 and led to the fourth discovery. Colour photos of a weta shown to us by climbers Jan and Arnold Heine provided the stimulus to head for the Southern Alps in search of a large brown species.
A helicopter lifted our party into remote Price’s Basin, a tributary of the Whitcombe. Jan, who was with us, led the way to a point at about 1350 m and indicated the sort of place where the photo had been taken. It was only a matter of minutes before a pair of giant weta was revealed, hiding in a shallow burrow under a stone.
In the course of the day, 36 individuals of the new weta were observed. They were of all sizes, indicating a healthy population. Not rare, they had simply eluded earlier naturalists by their inaccessibility and nocturnal activity. Our specimens matched up with us, led the way to a point at about 1350 m and indicated the sort of place where the photo had been taken. It was only a matter of minutes before a pair of giant weta was revealed, hiding in a shallow burrow under a stone.
In the course of the day, 36 individuals of the new weta were observed. They were of all sizes, indicating a healthy population. Not rare, they had simply eluded earlier naturalists by their inaccessibility and nocturnal activity. Our specimens matched up with several earlier ones which had been collected from other parts of the Southern Alps, and had been referred to as the Mt Cook giant weta.
History almost repeated itself in January of this year after the Mt Somers experience when I was again heading towards a mountain top in a helicopter, accompanied by a West Coast tour operator, Owen Dennis Owen had photographed a large weta on Mt Faraday in the Paparoa Range. Since there were no records of giant weta from there, his sighting was intriguing.
After what seemed like only a few minutes on the high granite slopes, Owen turned up a specimen. Is it yet another kind of giant weta? We cannot be sure yet, but there is a strong possibility that the Paparoa weta represents a new species, the fifth in the last 30 years. The age of discovery continues.
Interest in weta has never been greater. The reason? These cumbersome armour-plated insects—particularly the giants—represent another fragment of our unique New Zealand fauna, a fauna that is not coping well with modernity. We have lost over half our birds since humans arrived, and the largest of the weta totter on the brink of extinction. While weta may lack the cute and cuddly appeal of birds, they are the insect equivalent of the distinctively New Zealand moa, kakapo or takahe.
Giant weta represent a past era of animals which were heavier and slower than those of today. An age in which Aotearoa was home to large, flightless, ground-dwelling animals of many kinds—animals which had evolved in the presence of few predators. To be sure, these insects had to avoid the tuatara, large nocturnal lizards and a few insectivorous birds like owls, but during their millions of years of quiet evolution in the forerunner of New Zealand, they had experienced nothing so devastatingly efficient as the nocturnal, warm-blooded predator that arrived with the humans: the rat—first kiore, then Norway and ship rats.
The story is the same for so many native New Zealand animals. They could not cfoot it with the new invaders. Hence giant weta now remain only on protected islands or high in the mountains where the rats do not reach them. Some of the more agile hole-dwelling weta, however, have beaten the odds and survived despite the predators.
If you live almost anywhere in New Zealand except in Otago or Southland you are likely to have tree weta populations in your garden. These are the “street-wise” kinds of weta, fully capable of withstanding the stresses of modern living.
Their lives revolve around shelter holes in which they spend the daylight hours. Although they chew neatly and cleanly around the entrance, weta do not actually excavate their own tunnels. All sorts of holes are used. The second-hand tunnel of a large woodboring beetle such as a huhu grub makes an excellent retreat, but they are equally at home in the folds of corrugated iron or any dry crevice on the outside of a building. Or inside a gumboot, for that matter.
Ron Ordish, entomologist at the Museum of New Zealand, has been putting weta nest boxes in his garden in an inner Wellington suburb and monitoring tree weta comings and goings since 1988. His back yard always sustains over 30 individuals, and often as many as 60.
In the bush, you will find them inside hollow trees or in the hollow stems of just about any kind of plant. They enter head first, leaving the massive spiny hind legs blocking the passage to any intruder. In the evening, they back down the tunnel so that sense organs on their rear are able to assess the weather conditions.
Only if everything seems right do they venture out fully. Warm, damp, very dark nights without a moon are preferred. Activity is greatest in summer, but weta emerge throughout the year to feed and wander about.
Most tunnels are occupied by only one weta. However, given the choice, it seems they prefer to snuggle together in larger holes. Weta social aggregations are not haphazard. Adult males are in charge, and they welcome adult females as companions, and tolerate juveniles. But enter another mature male and all hell is let loose. A territorial fight ensues to establish which male is to be responsible for the accompanying females. Usually, the male with the bigger head wins.
Each “harem” is a loose association, since females do not show strong site or male affiliation. They can mate within the shelter with the dominant male, but may equally well find another male while out on their nocturnal walkabouts.
For an insect, a weta enjoys a long lifespan. It takes from one-and-ahalf to two years to develop from egg to adult, and then the adult weta may survive anything from six months to two years or more. Tree weta tend to live longer than giant weta. Equivalent-sized warmblooded mammals have a shorter life. A mouse, for instance, can expect to live only 18 months.
Female tree weta will lay eggs at almost any time of year except midwinter, but April and May are the peak times. This timing is related to the ease of burying eggs when the autumn rains soften the soil.
Females are distinguished by their long scimitar-shaped ovipositor or egg-layer. This structure is made up of several slivers of hard tissue which separate to allow an egg to pass down the centre. The female probes the soil with the ovipositor, testing its suitability, then thrusts it deep beneath her body before releasing several eggs at a time. In the course of her reproductive life she can lay as many as 300 eggs.
The eggs can hatch in as little as a month or remain in the soil throughout the winter, hatching some time the following spring or summer into tiny, jumping baby weta which scatter to make their own lives in the surrounding vegetation.
Their growth takes place over the next 12-18 months by a long series of moults. Like all insects, moulting is the only way they can increase in size. Each moult involves splitting their skin, working their way out of it, and finally inflating themselves to a bigger size before the new outer skin hardens. During the process the weta is excruciatingly vulnerable, so it happens under cover of darkness.
Insects typically undergo a fixed number of moults to reach adulthood—in tree weta, usually nine. However, Wellington zookeeper and weta enthusiast Paul Barrett has recently discovered some anomalies in weta growth.
Paul has been keeping weta at the zoo since 1986, and has established breeding colonies of giant weta from Mana Island, Mahoenui and the Poor Knights Islands, as well as a number of tree weta colonies.
Over the years, he has spent untold hours raising baby weta. Each is kept isolated due to their cannibalistic tendency when crowded. Careful measurements of this horde of adolescents has provided us with a fascinating growth story which may prove to be a world first.
It goes like this: Territorially successful male tree weta can be recognised by their excessively large heads—just as in stags or bull fur seals. This enables them to win fights with other males and thus gain control over a number of breeding females.
However, not all males have large heads. In fact, if you were to measure the head size of all the adult weta in a large colony, you would find a whole range of sizes for males from normal to huge, but with females all would be normal. You might suppose that the small-headed males would simply grow up to become big-headed males in the fullness of time (like stags or bull seals), but with insects that is impossible due to their moult system: once sexually mature they cannot moult again.And once their head has hardened after a moult it cannot grow. Thus there is no way that a small-headed, sexually active male can grow into a large-headed male.
Paul’s breeding experiments have shown that while it takes females nine moults to reach adulthood, it may take nine, eight, seven or as few as six moults to become a sexually active male. In other words, small-headed males have become sexually mature after fewer moults than large-headed males—hence the wide range of head sizes in males.
This capacity to reproduce before reaching full adulthood is known as neoteny and is virtually unheard of in insects. There are more details to be worked out, such as which factors determine how many moults an individual male will undergo, and what is the advantage of having a smaller head, but Paul has already shown that small-headed males do not miss out on breeding opportunities. Indeed, small-headed males often secure a partner while the bigheaded male is busy defending his territory.
Only the tree weta species have this sort of territoriality and enlarged male head size. In the more docile giant weta, both males and females have similar head measurements. They live solitary lives, and are not aggressive toward one another.
One of the most studied of the giant weta is Deinacrida rugosa, which lives on Mana Island, off Wellington’s west coast, and on two other islands in the region. Ever since the Department of Conservation eradicated mice from Mana Island in 1991, the giant weta population has flourished. The insects had coexisted successfully with the mice for over 100 years, but with reduced predation on young weta now the mice have gone, the weta population has boomed.
Mary McIntyre of Victoria University uses radio tracking to learn about the nocturnal movements of these weta. With the aid of a tiny transmitter attached temporarily to the weta’s back, she can follow female weta around all night long, and locate their hide-outs during the day.
Males are excused from carrying radios because they are not as big as females, but, as it happens, they are still included in the study. During late summer, Mary has found her radio-tagged females being trailed by one or two ardent males, following closely. One may eventually lay a leg across her back to stake his claim. The pair frequently spend the day in the female’s campsite.
During their nightly walkabouts the big mature females (reaching over 25 grams in this species) may wander up to 50 metres in a night—no mean feat in the long, dense grass. Lack of a regular home base or shelter hole distinguishes this and some other giant weta from tree weta, and perhaps explains why the giants have been so much more vulnerable to introduced predators than have the tree weta. The giant weta of Mana Island used to be found on the North Island at Wanganui and on Kapiti Island but has now been exterminated by rats at both localities.
Mary’s radio tracking also takes her to a remote island in the Mercury group off Whitianga, home of the Mercury Island tusked weta. Males of these large weta (9 cm body length) sport a pair of extraordinary tusks attached rigidly to their jaws. The tusks project forwards, and must be an awful curse during everyday life, but they come into their own for solving territorial disputes.
We had the good fortune to watch one of these battles in captivity when an outsider male was placed near a resident male in a large enclosure. The two met head-on, locked tusks and engaged in a pushing contest, each trying to upend his opponent. After some minutes, one lost its footing and was overturned. He crept away, vanquished but not physically damaged. Indeed, for all their fearsome weaponry, male tusked weta probably suffer less damage in this stereotyped fighting than do tree weta males in their jaw-biting contests.
Young tusked weta and females lack the tusks. On their remote 10-hectare island—the only habitat of this species in the world—tusked weta spend their daylight hours concealed in chambers which they excavate in the loose soil, back into, then seal with a soil-saliva plug over the entrance. They venture out only on pitch black nights, disappearing under cover as soon as the moon rises—a useful defence strategy given that the island is populated by tuatara and several kinds of large lizards who probably all enjoy weta on their menu.
Another quite different tusked weta lives in the far north between Cape Reinga and the Waipoua kauri forests. It is a tiny insect, reaching only 1.7 cm, but the male carries tusks just like the Mercury Island species. Nothing is known about its gladiatorial activities, but it is a hole dweller, occasionally turning up in manuka firewood.
Over the last five years, Jackie Davidson of Kohukohu has befriended and studied a number of tusked weta in her garden. Her first was “Charlie,” whom she found living in a hole in a Muehlenbeckia vine which hung beside her outside toilet. He occupied the hole rear end first, tusks and antennae out. Over a period of two years Jackie and her family came to regard Charlie as a member of the family. They noted that his tusks lengthened and straightened as he grew, that they were raised when the weta was agitated and lowered when he was relaxed, and other such details.
Jackie has caught several of these fascinating little Northlanders and observed their behaviour in captivity. Most seemed happy living in holes, which they periodically sealed over with pieces of bark so as to be virtually invisible. However, one female, “Mary,” who turned up on Christmas Day, made herself a cavity in the soil just like the Mercury Island weta. What other surprises might this relic, which hangs on to survival in the shrublands of the north, have for us?
A whole branch of the weta lineage has tended to escape the scientific limelight because of the retiring behaviour of its members. These are the forms referred to as ground weta. Known to science as Hemiandrus, they are mostly small (2-3 cm), although one from the Takitimu Range in Southland reaches giant weta dimensions at 6 cm.
The distinctive characteristics of these weta centre on their burrowing lifestyle. They spend their days in tunnels which they excavate in the soil. They can either enlarge burrows of other insects or worms, or make their own, but their tunnels are always very smoothly finished off. In some species the females brood eggs and hatchlings in an underground chamber—a most unusual behaviour for insects elsewhere in the world, but one present in a number of New Zealand species.
The ground weta group as a whole have a more cricket-like appearance than do tree or giant weta, due to the absence of heavy fixed spines on the hind legs. They also do not flick up their hind legs in defence. Lack of defence equipment and kicking ability does not imply, however, that these creatures lead peaceful lives. On the contrary, they are extremely aggressive towards one another. They enter their burrows tail-first so that the head faces any intruder. If aroused, they display an impressive wide gape of the sharp jaws.
Peter Johns of Canterbury University considers that there are about 36 species of ground weta in New Zealand, with others likely awaiting discovery.
The four categories of weta mentioned so far are all classified in the family Stenopelmatidae, which has an almost worldwide distribution. North Americans call them Jerusalem crickets or ground crickets, whereas in Africa or Australia they are king crickets. New Zealanders would easily recognise these overseas insects as cousins of the weta, although ours reach larger sizes.
As well as stenopelmatids, we have another kind of large jumping insect that is regarded as a form of weta. These are the cave weta, exceptionally long-legged, agile creatures which lurk in damp, dark places and leap vigorously when disturbed. Scientists place these insects in a separate family, the Rhaphidophoridae, distinguished by the fact that the bases of their antennae almost touch and they lack adhesive pads on their feet. Like ground and tusked weta, they lack heavy fixed spines on the hind legs.
Various kinds are found anywhere from the summits of high mountains (the Mt Cook “flea” is one) down to sea coast caves; in all, some 60 species are known. They are by no means restricted to caves, and are most often seen stalking about on the ground or on tree trunks on damp, mild nights. Even cave populations generally have access to the forest outside, where they make nightly foraging trips.
Although often encountered in masses by day (e.g. in an abandoned water tank) they are not highly social. Their aggregations seem to be simply a case of tolerating each other in a desirable roost. Territorial fighting is not part of their repertoire.
Extremely similar types of cave weta to the New Zealand ones occur in caves near Cape Town, South Africa, in the rainforests of Tasmania and eastern Australia, and from southern Chile—forming what is known as a Gondwanan distribution.This southern hemisphere pattern indicates that cave weta have been living in these places for more than 70 million years.
Just how unusual are our weta? It often takes an overseas visitor to alert us to the significance of what we have become familiar with. A British ecologist, Dr H. N. Southern, when visiting Little Barrier Island in 1964 and seeing a wetapunga for the first time, commented that he had been aware that moa were to the prehuman New Zealand environment what deer, goats and horses were to other parts of the world, but he had not realised that we had “invertebrate rats” as well.
Giant weta, he suggested, had occupied the niche elsewhere held by rodents. Common features between rats or mice and weta include their size, nocturnal foraging, daytime shelters, polygamy and diet. It is ironic, but not unexpected, that now these warm-blooded equivalents have been introduced to this country, they have supplanted the cold-blooded weta from its niche, and are largely to blame for their demise.
Iveta are omnivorous. All the tree and giant weta species can be maintained in captivity on an entirely vegetarian diet consisting of leaves of a wide variety of trees and shrubs and pieces of fresh carrot or apple. Most will also accept living or recently dead insect prey, but their heavy design and cumbersome rate of movement is not well suited for catching active prey. Ground weta are more active and are much more reliant upon animal prey, while cave weta are primarily scavengers, picking up bits of lichen and fragments of dead organic matter.
What goes in must come out, and weta droppings are not devoid of interest. Firstly, they are surprisingly large for the size of the insect—more like rat droppings than those of insects. However, their neat cylindrical form with rounded rather than tapered ends enables them to be distinguished from rodent or possum droppings. Field biologists thus have a quick way of detecting the presence of weta, and, by examining organic fragments in the droppings, can identify the kinds of leaves the weta has been eating.
The scent of the droppings is significant to weta. Odours permeate their lairs and tracks, enabling them to recognise their home territory. The smells may also enable males to find females. Animal scents that convey messages of this type are known as pheromones. Weta certainly use pheromones for communication, but little is known about this aspect of their biology.
Unfortunately, these days their odours reach the extremely sensitive noses of rats and stoats, which hunt their prey by smell. The weta olfactory communication system is thus contributing to their downfall.
More is understood about the role of sound in weta life. Frogs croak, bats and mice squeak, kakapo boom, crickets chirp and weta call “tsit,tsit, tsit” in the dead of night. No one would describe the sound as singing, a term used for grasshopper or cicada sounds, but the calls are a notable part of our nocturnal bush noises.
The technical term for noises of the weta kind is stridulation, which means that the sound is a vibration produced by rubbing together two parts of the body. Crickets and grass
hoppers vibrate their wings in order to chirp, but weta, being totally wingless, use their hind legs like the bow of a toneless violin.
Their musical instrument is made up from three parts: a file situated on the sides of the body, a scraper on the inside of the hind leg and a resonance chamber underlying the file. Although the structures are tiny, you can readily see them in use. When you disturb a tree weta, it goes through a ritual of leg-raising, during which it emits the short rasping notes of its defence call. If you watch carefully, you will note that it is silent during the upstroke of the legs, but that as the hind legs are brought rapidly down the sound is produced.
The tree weta species all have a file with a series of 4-9 parallel ridges. It is just visible on the side of the body at the point normally obscured by the thick muscular part (femur) of the hind leg. The scraper is a patch of microscopic pegs on the inside surface of the femur. The weta amplifies the sound by using air pressure to inflate the body rigidly in the vicinity of the file. Positioning the file over a taut air bag gives it a drum-like quality.
Weta sounds have fascinated Canterbury University zoologist Larry Field, who, since 1978, has been recording and analysing their “speech.” He has found that tree weta make the greatest use of sound for communication, and has made considerable progress in deciphering their language (see box page 108).
Male tree weta are professional aggressors. As juveniles they begin their “apprenticeship,” and as adults it dominates their lives. It shows in their big heads, heavy jaws and erect, head-high stance compared with females. Stridulation sounds are emitted during their pitched battles, which involve pulling opponents out of tunnels by the leg, kicking with the spine-covered hind legs, grappling, biting and lunging. Despite all the ferocity, relatively little physical damage is inflicted. At the conclusion of a bout, the victor stridulates triumphantly while the loser slinks away in dejected silence. Each male has to accept his place in society the hard way, but will always come back to have another go.
Giant weta use the same leg-kicking and rasping sound for defence as tree weta do, but their lifestyle is a solitary one, not based on the social hierarchy of tree weta. Thus, even in a dense population of giant weta, such as occurs on Mana Island, stridulatory sounds are seldom, if ever, heard.
As well as normal stridulation, giant weta have two further ways of producing sounds. One is a hissing noise generated by telescopic contraction of the body segments. The other is a ticking sound made while the legs are being held vertically in the threat posture. Male tusked weta are capable of a further type of sound, generated by rapidly drawing the tusks across one another to produce a rasping sound due to a series of tiny ridges in the zone where they rub together.
Weta ears are positioned not on the head but on the insect’s front knees, where they are visible as slightly sunken oval patches. This is a very practical position for ears, because their distance apart gives weta excellent stereo reception for working out what direction sound is coming from. Orientation of battling males in pitch darkness is almost certainly guided by sound.
Eyesight probably plays a limited role in weta—as would be expected for a nocturnal insect. Like all insects, weta have compound eyes, but how precise an image these form is not known. About all that has been observed is that weta can tell light from dark, and can also assess the intensity of darkness. For example, some types of weta will emerge from their burrows only on moonless nights.
Not all tree weta live in trees. Although North Island species are mainly forest dwellers, in the South Island more species are found in grassland than in forest. For one of the species that lives in treeless areas, this has meant quite an adjustment from the typical tree weta lifestyle.
The mountain rock weta, Hemideina maori, hides under stones instead of sheltering in tree holes, but in other respects is very much a tree weta. It has remained common despite the presence of rats, and it exhibits the social features of other tree weta. One fascinating difference, though, is the way it reacts to disturbance. The rock weta is able to raise its hind legs in defence, but more often will roll over on to its back. The exposure of its soft under-surface may not be as stupid as it first appears. If you try poking it with your finger you will find it swiftly swings all its legs up to grab the finger and sink its jaws in—a particularly painful experiment. Many a would-be predator has probably had this experience … just one of the many reasons why tree weta can be classed as more “advanced” than giant weta.
Recently the mountain rock weta made cryogenic history. A group of physiologists at Otago University had been testing the ability of this weta to withstand the freezing temperatures in its high altitude habitat. John Leader and Jennifer Bedford looked at the blood composition of specimens from the Rock and Pillar Range near Dunedin, and reasoned that they could probably tolerate temperatures well below freezing. What they discovered was that the weta could be frozen solid and yet return to life when thawed. Further research has shown that there is no evidence in the blood of antifreeze, which is often found in insects which survive freezing, so these in‑sects must have the ability to tolerate internal ice formation. The mountain rock weta is the largest known insect capable of this sort of winter survival.
Will do many people find weta such alarming creatures? Is their reputation as devils of the night really justified? Weta “demonstrations” at zoos and public gatherings prove that many people are capable of handling weta without fear, and soon become entranced by their lumbering gait and waving antennae. However, like many animals, if handled roughly or cornered, weta will bite and scratch in their attempts to escape.
The bites of large ones can draw blood. Sir Walter Buller gave us a graphic description in 1896 of a young man bitten by one of the common tree weta: “He was bitten on the wrist, and had an awful arm; indeed, the pain nearly drove him mad.” This was probably an exaggeration, but the golden rule for peaceful weta handling is not to grab them but simply to let them crawl. The pincer-like claws on the ends of the legs are extremely effective on rough surfaces, but will come free from, say, a jersey if you allow the weta to walk off of its own accord.
It is not difficult to study weta behaviour or keep them in captivity. A glass aquarium tank can be set up with rocks or leaf litter in the base and a few branches for the insects to climb on. Weta require fresh leafy food every few days, and are particularly partial to a slice of fresh carrot. Two-litre plastic ice-cream containers make the best cages but, of course, you cannot see what is going on inside. Make sure there are some small holes punched near the centre of the lid for aeration. Avoid making holes near the corners because an adult weta can brace itself across the corner and chew a neat escape hole in the lid if you give it a “starter,” but they cannot tackle the smooth plastic. For comprehensive instructions on weta husbandry, see Paul Barrett’s book Keeping Wetas in Captivity, published by Wellington Zoo.
Heightened public interest in weta has paralleled an increase in conservation activity. Forewarnings of the vulnerability of giant weta came from Sir Walter Buller when he wrote that wetapunga was formerly “abundant in the forests north of Auckland; but of late years (in 1871) it has become extremely rare. The natives attribute its extermination to the introduced Norway rat, which now infests every part of the country and devours almost everything that comes in its way.”
Today, several species of weta have been reduced to very small populations and could be in need of outside help if they are to survive. Though Little Barrier Island was declared a sanctuary for wildlife in 1895—the first legal protection offered (indirectly) for a giant weta species, since by then this island held the only remaining population of wetapunga—it was not until 1980, when the Wildlife Act was amended to include some insects and snails, that formal protection was instituted for individual endangered weta species. All species of giant weta, except the scree weta, were placed on the list, as was the Banks Peninsula tree weta.
Some biologists realised the need to actively do something to save vulnerable weta populations well before the legislation came in. Foremost among these was insect conservationist Mike Meads, who initiated DSIR’s studies of giant weta on Mana Island in 1971.
At that time, Mana was a private farm which was about to be taken over by the Department of Agriculture for sheep quarantine. The thought of regular shipments of building supplies, hay and food to the island from a rat-infested warehouse stimulated Mike to attempt a transfer of giant weta to another island. He chose Maud Island in Pelorus Sound, which was also rat-free, and in 1977 made the transfer of 43 giant weta of various ages. They accepted their new island and have steadily increased in numbers until today they occupy a large area of grassy shrubland.
Mike’s fear of rat infestation of Mana was vindicated when on two occasions rats came ashore. Fortunately, they were killed before they had moved far from the barge, and both islands remain rat-free.
This translocation of a vulnerable insect to a new protected site was a first for New Zealand. The other major effort to protect a vulnerable giant weta has taken place on the North Island mainland, with the gorse-dwelling Mahoenui weta. First, the Department of Conservation created a reserve around the gorse patches where it was found, then initiated a breeding programme so that populations of the weta could be established in less vulnerable situations. To date, this hashappened on Mahurangi Island off the coast of the Coromandel Peninsula, where some 300 Mahoenui weta were released last year.
Although some reassuring remarks can be made about weta conservation to date, future prospects for these oversize, outmoded monsters are unlikely to be bright. Threats to their existence will not go away without modern intervention technology. So far, we have learned how to eradicate rats from islands, move weta to safe places, and breed them in zoos. All will help to save them in the long term.
The good news is that no weta species that we know of has become extinct in recent times, and we are still finding new gentle giants.