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).