It is often said that New Zealand is dominated by birds, yet for every type of land bird in the country, there are more than 200 kinds of insects, with the total estimated to be about 20,000 insect species.
Insects are plentiful on sea coasts, forests and mountain tops, but in temperate climates like New Zealand’s, many are hidden underground, in rotten logs, or in places where you have to search for them. New Zealand’s insects also tend to be small and dull-coloured compared with the larger, brilliant tropical varieties, and can easily be overlooked.
A study of Cupola Basin, in Nelson Lakes National Park, showed that the mass of native grasshoppers above the treeline reached 32.5 kilograms per hectare. This was three times greater than the combined mass of introduced pests, deer and chamois. Even so, the grasshoppers did less damage to plants than the mammals.
Of the world’s 29 insect orders, 25 are represented in the New Zealand region. The four missing groups are restricted to very few localities worldwide, so their absence in New Zealand is not surprising. However, two of the most significant orders of winged insects – scorpionflies and alderflies – each have only a single species in New Zealand.
The number of species in the larger orders, such as the flies, beetles and moths, is what you would expect considering the country’s land area and temperate location. But the three freshwater groups – mayflies, stoneflies and caddisflies – are over-represented, meaning that their diversity exceeds predictions based on New Zealand’s size. This could be due to high rainfall during the islands’ evolutionary history, which has created a multitude of streams and rivers. By contrast, another aquatic group, the dragonflies, are relatively poorly represented, with 17 recorded species in New Zealand (of which 10 are found nowhere else).
There is an unwelcome abundance of small, black, biting sandflies (Austrosimulium species, called blackflies elsewhere) in wetter areas, their larvae breeding in swift, clear streams. Mosquitoes are also common in some places. New Zealand has no dangerous native stinging insects. Wasps and bees, introduced from Europe, can be a threat to some people.
The majority – more than 90% – of insects found in New Zealand are endemic – they are unique to the country. Few other places, apart from New Caledonia and Madagascar, have so many endemic species. This is due largely to New Zealand’s isolation in the South Pacific Ocean for tens of millions of years. Groups with the highest endemism (100%) are stick insects, mayflies, stoneflies and caddisflies, and lowest are groups like parasitic lice (20%), which are carried by their hosts.
Notable among the unique insects are wētā, which include the tree wētā (Hemideina species) and giant wētā (for example, wētāpunga or Deinacrida heteracantha). There are 18 species of these flightless, grasshopper-like giants – one species weighs 45 grams. They have been able to evolve in the absence of small mammalian predators such as rats. Like rats, they are long-lived, nocturnal, omnivorous, and often live in social groups. Their nearest living relatives are in Australia.
The New Zealand batfly (Mystacinobia zelandica) is a small, wingless, spider-like fly that lives in the roosts of the country’s endemic short-tailed bat (Mystacina tuberculata). Batflies have evolved in New Zealand from a blowfly ancestor, and depend entirely on the bats for food (bat guano), transport and shelter.
As every fly-fisher knows, caddisflies are common around streams and rivers, and are a favoured food of trout and other freshwater fish. Most of the 239 native species live near fresh water, but a few have taken to the sea. The world’s only marine caddisflies (Chathamiidae family) live on New Zealand’s coastal rocks. Their larvae inhabit rock pools washed by the tides, and feed on coralline seaweeds. There are five species of marine caddisfly, one of which has reached the east coast of Australia, probably carried on a ship’s hull.
A blind, earwig-like, six-legged arthropod (although not strictly an insect) is found in some parts of New Zealand, in rotten wood. Called Heterojapyx novaezealandiae, and not well known, it is probably the country’s most ancient arthropod. Almost identical fossil forms 300 million years old have been found in Canada. Heterojapyx qualifies as a ‘living fossil’, and is older than the native tuatara lizard.
Archaic forms of insect life have survived well in New Zealand. They include the most primitive types of dragonfly (Petaluridae), plant bug (Peloridiidae), moth (Micropterigidae), scorpionfly (Nannochoristidae) and cranefly (Tanyderidae).
To a visitor, New Zealand might seem to have few butterflies. Compared with Australia, where there are 364 species, New Zealand’s selection is small. There are fewer than 20 species of native butterfly; 12 are recognised species, but the others have not been formally described. Apart from the ubiquitous red admiral (Vanessa gonerilla), seen in parks and back gardens, native species live in more remote mountains or along rocky coasts and riverbeds.
Although most insect types are represented in New Zealand, there are some notable exceptions. Inexplicably, social insects are either absent altogether or, if they are present, they are uncommon and the number of species are few.
Social bees do not occur except where they have been deliberately introduced, but there are 28 species of solitary native bees. These are smaller than introduced bees and have short tongues, which limits the flowers they can pollinate. They gather in large numbers on the blossoms of mānuka and pōhutukawa trees.
Social wasps are not part of the native fauna, but a few exotic types have been accidentally introduced. Two species of aggressive black and yellow wasps (Vespula germanica and V. vulgaris) are now established throughout New Zealand.
Ants and termites are the only truly social insects in New Zealand. Only 11 of 39 species of ant are native. This small diversity is surprising considering the country’s proximity to Australia, where there are almost 10,000 species. Ants prefer warmth and sunshine, and climate cooling during the Pleistocene ice ages may have destroyed an earlier ant fauna in New Zealand, leaving only a few species that could tolerate the cold.
Only three species of native dry-wood termite are known in New Zealand, compared with more than 300 in Australia. Dense colonies of these small white insects, numbering many thousands, can be found inside decaying wood, usually on the forest floor. They are a primitive type of termite, lacking the impressive building skills of the more advanced species, but still with castes of soldiers, immature workers and reproducing adults. The adults are winged, and mate briefly in swarms. They then bite off their wings in order to burrow and establish new colonies.
It is difficult to account for New Zealand’s unique insect life. There are three possible scenarios:
Virtually no insect fossils have been found in New Zealand, so it is often a matter of speculation when and how insects arrived. However, DNA research is providing a better picture of the history of certain insect types. Some are claimed as ‘founding’ members of the New Zealand fauna, where the evidence indicates that they were around when New Zealand drifted away from Gondwana. Wētā are one of these groups, and the DNA of a worldwide family of primitive, pollen-feeding moth (Micropterigidae) suggests that they were also in New Zealand when it split from the supercontinent.
Some of the insects that live near water in New Zealand have relatives elsewhere. Cool, clear New Zealand streams and rivers are the habitat of about 350 species of aquatic insect larvae, all of which eventually become winged adults. They include mayflies, stoneflies and caddisflies, and the sandfly Austrosimulium, midge larvae (Chironomidae family), some water beetles, a scorpionfly, Nannochorista and the alderfly Archichauliodes diversus, which has ferocious-looking larvae known as ‘toe biters’. They are the lifeblood of the rivers, providing important food for waterfowl like blue duck, and for native and introduced fish. These insects have their nearest relatives around the southern hemisphere, from Chile to eastern Australia and Tasmania. It is thought that they were formerly part of a freshwater fauna from an area that included Antarctica in the days before New Zealand became isolated and Antarctica became ice-bound.
Many New Zealand insects have their nearest relatives in Australia. There is no certainty when they came, but there can be no doubt that dispersal across the Tasman Sea accounts for a significant number of arrivals.
Every now and again new insects arrive, wafted on the strong westerly winds that circle the Southern Ocean. Long oceanic journeys may seem implausible for these tiny, land-based creatures, but a number are recorded every year. In 2000, more than 1,200 alien insect species were living in New Zealand.
The best-known travellers are butterflies and moths. Some, like the North American monarch butterfly (Danaus plexippus), became established in New Zealand in the 1870s. Others, like the painted lady (Vanessa kershawi) and blue moon butterfly (Hypolimnas bolina nerina) are regular visitors. In the two latter cases, breeding in New Zealand has never been successful, despite a plentiful supply of the plants eaten by their caterpillars. Painted ladies arrive in early spring, when the species is migrating in eastern Australia. Blue moons arrive in the autumn. Their journey can take as little as 40 hours if wind strength is about 30 knots.
Do Australian insects fly to New Zealand, or are they transported on ships or planes? To answer, you need to catch them at sea, before they reach land. When the Sedco oil-drilling rig was stationed 40 kilometres west of Taranaki in 1970, a volunteer, J. S. Benyon, caught Australian moths (mostly greasy cutworms) during westerly winds. He sent them to Dr Ken Fox, a Taranaki entomologist, who proved that the moths were flying across the Tasman Sea.
By 1978, 22 species of Australian moths had been recorded in New Zealand. Several were regular visitors, including the white ‘speckled footman’ moth (Utethesia pulchelloides vaga), the bogong moth (Agrotis infusa), and the greasy cutworm (Agrotis ipsilon aneituma), all of which bred in their new home for a generation or two before dying out. Occasional flights across the Tasman Sea have also been made by dragonflies such as the bright red Diplacodes bipunctata, and various crop aphids such as the grain aphid (Macrosiphon miscanthi).
Cicadas are one of the very few insects that have been researched in sufficient detail to confirm their mode of arrival. According to DNA research, two dispersals account for the origin of New Zealand’s cicadas. About 40 species of these sun-loving songsters are known to be native.
A North Island cicada, Kikihia scutellaris, common on the hills of Wellington, reached Picton in 1966 and is now spreading rapidly across Marlborough. They are thought to have travelled on the Cook Strait ferry, possibly as larvae in a potted plant.
One species arrived from Australia well before the ice ages, about 10 million years ago, and gave rise to four species that are able to tap their wings on the ground while singing. These include the country’s largest cicadas, one of which, Amphipsalta zealandica, choruses loudly in late summer.
Another founder, with its nearest relatives in New Caledonia, arrived at about the same time and has given rise to all the smaller green and black cicadas (Kikihia and Maoricicada species respectively) that can be heard in sand dunes up to high alpine zones.
New Zealand has an unusually high number of wingless, or at least flightless insects whose Australian relatives may be winged. The stick insects (order Phasmatodea, 21 species) are all wingless, as are wētā and most grasshoppers and crickets (of 109 species, five are winged).
Large, short-winged, flightless grasshoppers are extremely abundant in the tussock grasslands of the South Island, where their feeding can have a significant impact on herbaceous plants. New Zealand’s mole cricket or honi (Triamescaptor aotea) is the world’s only mole cricket without wings. Elsewhere, these burrowing insects rub their wings together to produce a loud mating call, but in New Zealand they are silent. It is not known how the voiceless species seeks a mate.
Flightlessness is common in moths (usually only the females), as it is in beetles, wasps, cockroaches, earwigs and stoneflies. On the subantarctic islands nearly 40% of insects have lost the ability to fly.
Being wingless, the female alpine tiger moth Metacrias remains in her cocoon, surrounded by the eggs that she has laid. The tiny hatchling larvae then proceed to eat her. Her energy is recycled to give the larvae a strong start in life – as herbivorous caterpillars.
Flightlessness in stoneflies (order Plecoptera) is associated with low temperatures and high winds. In southern New Zealand, especially where rainfall is high, many stoneflies have left freshwater streams to live among snow tussock or under stones. The adults of 25 of the 104 New Zealand and subantarctic species are wingless or have reduced wings. This contrasts with Australia, where only one of the 196 species is flightless.
New Zealand’s insects are usually active year-round. The surrounding oceans temper the climate and contribute to regular rainfall. Winters are relatively mild, and many forest trees are evergreen. Only a few insects in New Zealand need a dormant phase (diapause) to withstand winter.
Some subterranean larvae are most active in winter. These include grubs of the chafer beetle (Costelytra zealandica, or grass grub) and caterpillars of the Wiseana moth (porina caterpillars). Both are native insects which have become pests, because the larvae feed on introduced pasture and clovers.
Some of New Zealand’s insects have adapted to survive the unpredictable climate. Copper butterflies (genus Lycaena) produce broods made up of normally developing and diapausing larvae (which stop growing for many months). If the normal larvae die off in bad weather, the diapausing larvae will replace them. Alpine wētā can freeze solid over winter and thaw out when the weather improves.
The bush is home to many of New Zealand’s insects. They can be found tunnelling in wood, feeding on leaves, flowers or seeds, or in the fungi, litter or soil below.
The green pūriri moth (Aenetus virescens), the country’s largest moth, is found only in the North Island. Its caterpillar spends a year on the ground among decaying logs, and then climbs a tree trunk to excavate a short tunnel, where it spends the next two or more years. From this tunnel, which is sealed with a silken cap, the caterpillar feeds on the cell layer just beneath the bark. Because these cells regenerate, the caterpillar can survive in the same tunnel until it emerges as a moth. Moths have a wingspan of 13–15 centimetres. Unable to feed, they live only about two days.
The huhu beetle (Prionoplus reticularis), a species of longhorn beetle, is a large bush insect. Its larvae chew into recently dead rimu wood, leaving it riddled with holes. The grubs, as long as your little finger, are a favourite food of the kākā bird, and formerly of Māori. Huhu beetles have adapted well to introduced pine forests and thrive on pine wood.
The giraffe weevil or tūwhaipapa (Lasiorhynchus barbicornis) can be found where karaka or ribbonwood trees grow. Their grubs bore into the recently dead timber of these trees. Adult weevils show marked sexual dimorphism. The male proboscis is up to 3 centimetres long and carries the jaws and antennae at its tip. The female uses her shorter, 1-centimetre proboscis to drill holes into wood for laying eggs. The antennae are some distance back from the tip, leaving the end free to dig the hole.
Exposed shrublands, tussocklands and rocky areas above the treeline are home to some of New Zealand’s endemic insects. Many of these are dark with dense hair, which allows them to absorb the sun’s energy. Included among them are butterflies, grasshoppers and cicadas, which could be described as sunbathers.
The black mountain ringlet butterfly (Percnodaimon merula) rests on warm rocks or floats lazily in the warm air just above a rock surface. They lay their eggs on stones, and the pupae form under thin, flat rocks that heat up in strong sunlight. Caterpillars feed on blue tussock.
Large, flightless grasshoppers are common in the alpine zone. The highest-living alpine grasshopper, Sigaus villosus, is grey and covered with short hair, blending into its rocky habitat. It frequently jumps into tarns, where it floats, or onto snow patches, where its long hind legs work like ski poles to propel it to safety.
Bristly, black cicadas, known as Māori cicadas (Maoricicada species), occupy the same habitat. They are the highest-living alpine cicadas in the world.
Insects often have a chemically complex relationship with the plants they eat, and become dependent on a single type of plant. Black and white alpine weevils in the genus Lyperobius depend on speargrass (Aciphylla), a relative of the carrot. Their larvae tunnel inside the taproot, while adults eat the leaves. Seventeen species of large, flightless Lyperobius are distributed throughout the South Island mountains, each eating particular species of speargrass or its near relative, Anisotome.
Among the foreign insects that become established in New Zealand, some endanger native plants animals, some are harmless, and others pose economic or health threats. Costly aerial spraying of urban areas targets those species of serious concern, such as the painted apple moth (Teia anartoides), the white spotted tussock moth (Orgyia thyellina), the gypsy moth (Lymantria dispar) and the salt marsh mosquito (Aedes camptorhynchus). The remainder are tolerated because eradication is not possible.
The introduction of some insects has been deliberate. Early settlers realised that without native long-tongued (pollinating) bees, the fruit trees and crops they had brought from Europe would not become established. The honey bee (Apis mellifera) was introduced in 1839 by Miss Bumby of Hokianga, the sister of the Hokianga missionary John Bumby. The bee became widespread, even in native forest and shrubland.
From 1885, four species of European bumblebee (Bombus species) were released. One (B. terrestris) became widespread, but the others (B. ruderatus, B. hortorum and B. subterraneus) although successful, were more restricted in their distribution.
Biological control of insect and plant pests began in 1874, when the eleven-spotted ladybird (Coccinella undecimpunctata) was released to control aphids. By 1991, 242 foreign insects had been released for biological control, 75 of which became established. Between 1991 and 2006 a further 12 species were released, all of which seemed to be successful. The native grass grub holds the record for being the most persistent pest: 24 biological agents were released against it between 1921 and 1981, but none became established.
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