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.
Butterflies and moths
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.