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Inr. Zoo Yb. (1992) 31: 30-36 0 The Zoological Society of London

Maintaining and breeding the Common tree weta

at Wellington Zoo Hemideina crassidens

PAUL BARRETT Zoo Keeper, Wellington Zoological Gardens, Newtown Park,, Wellington 2, New Zealand

The New Zealand wetas are orthopterans, distantly related to the cricket, and classi- fied into two families, the Rhaphidophor- idae, cave wetas, and the Henicidae, tree and ground wetas, which include the genera Deinacrida and Hemideina (Richards, 1973). The giant wetas Deina- crida spp include D. heteracantha the largest and heaviest insect in New Zealand and among the largest insects in the world. Six species of Deinacrida were mentioned by Richards (1973) and five are included in the IUCN Red List, four in the Vulnerable category and one as Inde- terminate (IUCN, 1983, 1990). Since 1983 a further five species have been recognized all of which are threatened. In the Herni- deina, the Banks Peninsula tree weta H . ricta is known only from a small remnant population and a number of other species and genera are regarded as in need of research and positive action. A Recovery Plan to include a management programme for both wild and captive populations is at draft stage and future plans include the appointment of a recovery group leader and a captive co- ordinator (Garland & Butler, 1991).

As part of this Recovery Plan a breeding programme has been established at Wellington Zoo. On 27 July 1986 ‘Project Weta’ was initiated with a non- threatened species, the Common tree weta Hemideina crassidens, (Fig. 1) as a model. The observations on this species reported here are being used as a basis for the next stage of the programme.

In size H . crassidens is typical of its genus; the adults range from 40-70 mm in

length and from 3-7g in weight. It is widespread ranging from the Central North Island to the western side of the South Island. It probably owes its survival to its ability to hide in holes which preda- tors cannot enter although it is also capable of defending itself; usually it will drop out of foliage to escape but it will also bite strongly if attacked. Important predators are introduced rodents, rats and mice, as well as owls, such as the More- pork Ninox novaeseelandiae, and in its egg and nymphal stages it may be taken by predatory beetles (carabids) and spiders, such as Miturga and Porrethele.

It occupies a wide range of holes and crevices in living and dead trees and, although it is capable of making a hole for itself, it usually enlarges those of wood- boring insects. It forms harems, consisting of an adult d’ with up to ten 99. It is essentially an arboreal species and, except for harem-holding adult dd, tends to wander. It is nocturnal, emerging at night to feed on living foliage, bark, flowers and fungi, and dead leaves. Berries are also consumed and it is fond of insects both dead and living.

The 22 specimens which formed the founder group at Wellington Zoo were collected from the wild in July when the species is comparatively inactive in the cool winter conditions.

HOUSING At the Zoo the colony was housed in three glass aquarium tanks measuring from 60 x 30 x 30 cm high (housing 1.4 insects) to 12Ox48x48cm high (housing 2.8

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/'

/'

Fig. 1. The Common tree wet8 Hernideina crassidens.

insects) and a smaller glass container 30 x 30 x 30 cm (housing one pair). As the insects are capable of chewing through plastic or wood, the tanks were covered with galvanized steel and fine steel mesh lids.

As this species lays its eggs in the ground, the enclosure substrate was soft friable soil to a depth of 50mm and mounded in the middle to assist drainage.

Leaf litter was sprinkled on top both to give the wetas 'occupational therapy' and to help control possible degeneration of the tarsi which can occur from walking on bare soil. Branches of Coprosma or Myo- porum were supplied allowing the wetas to climb about the enclosure and providing bark for chewing and mating sites (Fig. 2).

A special harem gallery (Fig. 3) was made from a small log 450 mm long cut in

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,A -. V Fig. 2. Accommodation for 1.4 specimens of Hemideina crassidens. A.stee1 lid with steel insect mesh for ventilation; B. glass tank, 60 x 30 x 30 cm high; C.barem gallery (see Fig. 3); D.chbing braoches, E. Bnx shelter; F. leaf litter; G. cotton wool wad for water; H. jar lid for water; I. green foliage for food; J. friable top soil.

half horizontally with a channel and chamber cut into the bottom half which was covered with a sheet of perspex before the top of the log was replaced. The entrance hole was 20 mm in diameter. Additional shelter outside the gallery was provided by cutting flower stalks of flax Phormium tenax into 150 mm lengths, splitting them in half to remove all but

Fig. 3. Harem gallery made from a 450 mm log: A. lid; B. bollowed+ut cavity; C. perspex inspection cover; D. entrance; E. cutdown nail to stabilize lid.

30 mm of the central core and securing the two excavated sections together with rubber bands. The almost hollow stalks were then pushed into the soil against the gallery and proved useful for 99 to hide away.

This species is tolerant of a fairly wide range of environmental conditions. We found the that the acceptable temperature range was 10-25°C. Below 10°C the wetas became largely inactive, although they would leave the shelter and feed periodi- cally. If the temperature rose above 25°C they would abandon the gallery to seek a cooler area in the leaf litter.

The wetas appeared comfortable when humidity was kept to 6&70%. Below this range they would eventually abandon the gallery and above 70% the gallery would become soiled and uninhabitable. The desired level was maintained by misting the enclosure every second day in dry weather and every four to five days in cool or damp weather.

FEEDING This species is omnivorous but the staple diet is fresh green foliage. A wide selection of different leaves is consumed in the wild but there is a preference for native plants. The insects feed readily on flowers, bark, fungi, fruit and insects in the wild and a varied diet was planned for the captive programme (‘Table 1). The feeding regime was based on observations in the field by the author.

Foliage was provided in the form of fresh sprigs of eight to 15 leaves in a dish or small container of water. Dead leaves were available in the leaf litter. Fruit, in the form of apple, banana or berry fruits, was provided once or twice a week and placed on a large dead leaf. Strips of ox heart (30 x 40 mm), dead newborn mice, dog sausage and dead insects were also offered on a leaf. Live insects were put into enclosure as food but larvae or grubs were killed to prevent their burying them- selves in the soil. The food was changed every two days and each item replaced with a different one. Water, which is

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DAY DIET OFFERED

Monday mahoe taupata plantain locusts Tuesday ngaio butterfly bush kohekohe apple Wednesday lacebark manuka kowhai crickets Thursday willow veronica euonomous mealworms Friday kanuka taupata ngaio large moths Saturday kohekohe plantain mahoe katydids Sunday kowhai willow veronica dog sausage

ngaio Myoporum laetum; mahoe Melicytus ramijlorus; taupata Coprosma repens: kanuka Kunzea ericoides; manuka Leptospermum scoparium; kowhai Sophora sp; kohekohe Dysoxylum spectabile; veronica Hebe speciosa; butterfly bush Buddleia davidii; lacebark Hoheria populnea; plantain Plantago lanceolata; puha Sonchus oleraceus; dandelion Taraxacum ojicinale; buttercup Ranunculus repens; willow Salix babylonica; chickweed Stellaris media; euonomous Euonomous sp; wax weed Hydrocotyle sp. Table 1. Typical week’s feeding regimen for adult Common tree wetas HemiL.. ina crassidens and list of plants lsed in feeding wetas at various growth stages (see text).

essential to wetas, was provided in shallow lids of jars or by misting the foliage and attaching soaked pads of cotton wool to branches.

BREEDING COLONY The wild-caught wetas were organized into harems with four 99 to each S. with one pair housed on its own. The enclo- sures had been prepared in advance and once acquired the wetas were placed immediately into their quarters. By September the dd began to show an interest in the 99 and harem behaviour commenced. Copulation was accom- plished throughout the spring and summer months from September through to the beginning of autumn in March. Eggs were seen to be laid in April and May.

Copulation The 3 will occasionally copulate with the 99 in the harem gallery but most mating takes place in branches or foliage near the shelter and this was also the case with the captive group. Copulation is brief but quite complex: on locating the 9 the S. will attempt to pacify her by touching her body repeatedly with his palps. During this operation he will

pause momentarily to carry out a curious shuddering motion and then resume the touching. The shuddering encourages the 0 to be more receptive, which she indi- cates by remaining still.

Continuing his attentions, the 6 feels for the end of the 9’s abdomen with his own. He then draws back until he is facing in almost the opposite direction to the 0 and hanging from her and the branch. Connection then takes place and continues for about one and a half minutes. It is broken by either animal. When mating is terminated by the S. he is often aggressive and will threaten to bite. The 9 moves off abruptly and the 8 stridulates emitting a series of short stut- tering sounds by rubbing his abdomen against his hind femurs. A second mating may take place during the same night and the 0 will mate many times throughout the summer months.

Oviposition and hatching The ?Q gained weight in late summer and were heavy with eggs by March. Approximately three weeks before oviposition, we noted an increase in animal protein in the 9’s food intake and we increased the number of insects, which were taken readily.

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In April the 99 began to spend some one to three hours each night laying eggs. These were deposited in the soil substrate, positioned vertically or at c.45" to the vertical at a depth of between 9 and 23 mm. The 9 spent some time feeling and palpating the soil before laying and many exploratory dips of the ovipositor were observed. The eggs are black, cigar shaped and 5-63mm in length. They remained in the soil throughout the winter and hatching began in October.

The emergence of newly hatched weta nymphs was first noted on 16October 1987 and continued until 27 December giving a total of 80 young. During the hatching the adults were removed to prevent possible predation of the nymphs.

Care offirst to fifth instars Weta nymphs will attack and eat other nymphs and through the first five instar stages the young were housed individually in 100 x 100 mm containers. Leaf litter offered hiding places as well as providing a medium which would help to keep a moist micro-environment. Plastic airline tubing, 5mm in diameter and cut into 20 mm lengths, provided hiding places during the day and allowed us to keep an easy check on numbers without undue disturbance to the animals. This method, however, was not practical after the third instar stage for, although the tubes were replaced with larger ones, as the nymphs grew they showed a stronger preference for hiding in leaf litter and avoided the tubes.

While the nymphs used the tube shelters cleaning of the containers was made simple but once they began to use the leaf litter great care was needed to locate the animal before disposing of any rubbish from the containers. Faeces were deposited around the sides of the container, which were cleaned with a damp cloth.

The nymphs were fed every second day with a wide range of plant and animal material. Water, both for drinking and to maintain the required humidity, was

provided by misting the plant food at each fresh feeding. Plant material consisted largely of the common lawn weed, wax weed Hydrocotyle americana, which was dug up in large clumps and divided into smaller portions for each container. Chickweed, dandelion and plantain were also offered. The food plants used all wilt quickly and need to be replaced by the second day. Animal material consisted of freshly killed or live maimed insects. Small moths, midges, house-flies, caterpillars, aphids and cricket nymphs were all popular and the weta nymphs readily accepted insect as well as plant food. Unnatural foods such as dog sausage, apple and lettuce were offered but in moderation as the nymphs quickly became addicted to these items at the expense of more natural foliage and insects. The unnatural food was used once or twice a week and was always offered in conjunction with natural items. The nymphs grew well on this diet but by the sixth instar, their preferences changed and the diet needed to be adjusted.

Care of sixth instars At this stage the weta nymphs were treated on the whole as adults with regard to most of their care and feeding. Now 30mm long, they were more robust and easy to locate. They were rehoused, again individually, in larger containers (2 litre ice cream boxes) still with a leaf litter substrate but with the addition of pieces of bark rolled into a tube or pieces of wood to provide more substantial shelters. These were used constantly by the nymphs. The adult diet was acceptable to the nymphs from this stage onwards. The Hydrocotyle was largely ignored and, since it apparently caused digestive problems, as evidenced by prolapse of the rectum and scouring, it was discontinued. Dandelion, lettuce and chickweed were also removed from the diet. Normal adult fare, such as mahoe, comprosma, hebe, willow, ngaio, euono- mous and plantain, were offered. Insects were still relished and in addition to those fed at the earlier stages, larger items such

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as adult crickets, mealworms, locusts, cicadas, katydids and the grubs of large moths and beetles were added. Dog sausage, newborn mice and ox heart were also consumed. Food was offered every second day and unnatural food once a week. As for the adults, as well as misting water was provided in shallow lids and on cotton wool pads. Consumption of bark, flowers (buttercup, roses, broom) and dead leaf litter was also apparent and was encouraged.

ECDYSIS Up to the fifth instar, nymphs moult approximately every four weeks. After this, the interval lengthens to two to three months. The nymph increases in weight and size with the abdomen in particular distending. Having fed well, two to three days before ecdysis, the nymph reduces its intake or stops feeding. At the same time i t becomes more subdued and unwilling to defend itself. The exoskeleton becomes slightly paler, the thorax and abdomen become wrinkled and the exoskeleton appears stretched. At this stage the moult is one to two days away.

The changes in the insect’s body are timed for moulting at night. The excu- vium splits along a distinct ecdysal line, which is visible running dorsally along the three thoracic segments and over the cranium. Before the moult, the insect will venture out onto branches or the insect- mesh cover and grasp the surface with most or all of its legs. The moult itself will take from two to six hours to complete depending on temperature and humidity; during the moult period the recommended humidity is towards the upper end of the range (70%) but no higher. After moulting, if the nymph is not disturbed, it will consume all or most of the excuvium; an interesting observation as in our experience other insect omnivores, such as crickets, earwigs and cockroaches, usually leave their excuviae.

After moult, the abdomen is thin and withdrawn but begins to fill out again once feeding has begun in earnest. Often

older wetas do not recommence feeding for two to three days, although first and second instars often feed the night after ecdysis. The Common tree weta takes between 13 and 18 months from hatching to reach the adult stage.

As nymphs, wetas have considerable abili- ties to regenerate lost or damaged limbs, palps, cerci, antennae and tarsi, which gradually redevelop after each ecdysis. A damaged knee joint, however, can be entirely repaired by the next ecdysis and a lost antenna can be replaced by a new one three-quarters longer than the broken antenna at the next ecdysis. If an appen- dage is lost one or two instars before the weta becomes adult it will have only a partially regrown appendage which will not grow further.

AGGRESSION, DEFENCE & COMMUNICATION The typical threat posture, raising of hind legs, the subsequent slashing downward movement and associated stridulation, is apparent from the third instar onwards. Even second instar nymphs may threaten but they usually prefer to run away or ‘freeze’. A kick-back action of the hind tibiae is used by the first instar onwards to discourage another weta from attacking or evicting it from its shelter or against enemies of other species. The threat display is readily used by fourth instars and stridulation is clearly audible at this stage. By the third instar the nymphs can communicate with nymphs of their own age and older stages.

The eviction behaviour has brought about an adaptation in large nymphs and adult 99. Males use their mandibles to evict the less assertive 99 and nymphs by grasping their hind tibia and these have become thicker with heavier spines than the corresponding appendages on adult dd and are less prone to damage.

As the first captive generation of nymphs matured they were organized into harems.

REGENERATION

FIRST GENERATION HAREMS

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Any dd which matured before 99 were left in their separate accommodation until sufficient 99 were ready. Seventy of the 80 hatchlings survived to adulthood and many were distributed to other interested individuals and organizations, including Cologne, London and Stuttgart Zoos. Ten 86 and 30 99 were retained for breeding purposes.

The young 66. were introduced into breeding enclosures and once a d was settled in, one 9 was introduced each day until a maximum of four was reached, the gradual introduction preventing skir- mishes over territory. The new harems were formed in December 1988 to February 1989 ready to breed the following summer. In April and May 1989 eggs were laid and treated exactly as before. The second generation hatched in October to November 1989 and of a total of 586 hatchlings, a total of 274 survived to adulthood.

FUTURE With the successful establishment of a completely captive-bred generation, we were encouraged to terminate the breeding programme for this more common species and concentrate our efforts on threatened wetas. The adult H. crassidens were released into the wild and the recovery of marked individuals several months later indicated that the insects were capable of surviving in natural conditions.

Work with the Common tree weta proved extremely instructive and we believe that these experiences can be usefully applied when learning husbandry techniques for more endangered species, in particular in relation to the Banks Peninsula tree weta and even for members of the Deinacrida. Work has begun on

establishing breeding colonies of H. ricta, Poor Knights giant weta D. fallai, Stephens Island giant weta D. rugosa, Mahoenui giant weta Deinacrida sp and the Northland tusked weta Hemiandras monstrosus (name under review).

We recommend that any breeder proposing to carry out work on an endan- gered weta species, should first gain experience with the Common tree wetas. Although not generally considered a diffi- cult species to keep in captivity (Barrett, 1991), it presents ample challenge to anyone interested in working with these unusual insects.

ACKNOWLEDGEMENTS

I would like to acknowledge the kind assistance of Ron Ordish, Curator of Entomology, National Museum, Wellington, and Dr Graeme Ramsay, Plant Protection Division, DSIR Auckland, for their assistance and advice during the H. crassidem breeding project; my thanks also to Keith Taylor, Head Gardener, Wellington Botanic Gardens for preparing the list of plant names.

PRODUCT MENTIONED IN THE TEXT

Lucky Dog Sausage: manufactured by Lucky Pet Foods, PO Box 90, Auckland, New Zealand.

REFERENCES BARRETT, P. (1991): Keeping wetas in captivity. Nos 1-9. Wellington: Wellington Zoological Gardens, Department of Conservation New Zealand and New Zealand Entomological Society. GARLAND, P. & BUTLER, D. J. (1991): Captive breeding index if New zealand native fauna. Christchurch: Orana Park Wildlife Trust for CBSG. IUCN (1983): The IUCN invertebrate red data book. Gland: IUCN. IUCN (1990): I990 IUCN red list of threatened animals. Gland and Cambridge: IUCN. RICHARDS, A. M. (1973): A comparative study of the biology of the giant wetas Deinacrida heteracantha and D. fallai (Orthoptera: Henicidae) from New Zealand. J. Zool, Lond. 169 195-236.

Manuscript submitted 6 January 1992