Overview of White-spotted Tussock Moth in New Zealand

After white-spotted tussock moth (Orgyia thyellina) was discovered in Auckland's eastern suburbs in April 1996, the Government decided to take the once-only opportunity to eradicate it.

The tussock moth is a member of the same family (Lymantriidae) as gypsy moth, which is a serious forest pest in North America. It is native to Japan, Korea and Taiwan and possibly also China and the Russian Far East but not a serious pest in those countries.

As far as it is known, the white-spotted tussock moth has not been successfully introduced either accidentally or deliberately to any country (apart from New Zealand) outside its natural range.

Dave Bartram Surveying
Auckland gardens in April 1996

Its discovery in Auckland presented a serious potential risk to the New Zealand environment and economy. There are many examples of pests which, when introduced to new environments without their normal predators and parasites and with a whole new range of hosts, have caused enormous damage. The possum is probably the best known example of this in New Zealand.

Feeding trials after the discovery of tussock moth in Auckland have confirmed its leaf-eating caterpillars would damage trees and shrubs in parks, streets and private gardens. They could also seriously damage willow trees used extensively in New Zealand for shelter, soil and water conservation. Organically grown horticultural products would also be affected.

Left alone, scientists believe the white-spotted tussock moth would spread throughout the country in 5 to 10 years. This would have environmental, trade and health implications.

In response to this risk, the Government decided upon an eradication programme which included a combination of aerial and ground spraying in its first year. In its second year, the programme was focused on high density trapping to find out if and where any tussock moths remained.  The programme ended in June 1998, having successfully eradicated the pest from Auckland's eastern suburbs.

The Life Cycle of the Tussock Moth

The white-spotted tussock moth goes through up to three generations in a year.

The first two generations produce winged female moths. The female mates with a male moth and lays between 50 and 300 eggs which hatch within a few weeks. Both female and male moths die a day or two after the eggs are laid. These eggs are likely to be found on leaves and twigs but might also be deposited on vehicles, outdoor furniture or buildings.

The last generation of females is flightless. After mating with a male moth, the flightless female lays her eggs directly onto the pupal case (chrysalis) from which she emerged.

The eggs of the flightless female are laid in autumn and don't hatch until spring. These over-wintering eggs are usually found in sheltered places such as under the eaves of houses and garages. Pupae can also be found in sheltered places or wrapped up in dead leaves still hanging on trees.

White-spotted Tussock Moth

What to look for

Tussock moth lays clusters of white to buff coloured eggs, which look like tiny clay pots about the size of pin heads. Each mass will contain 50 to 300 eggs and will be about the size of a ten cent coin. Eggs are usually laid on the brown felt-like cocoon from which the female moth emerged. They tend to be found in sheltered spots on fences, buildings, trees and shrubs.

Eggs laid on a pupal case by the female moth

When it hatches the caterpillar looks like a black and very hairy ant. As it grows, the caterpillar develops an orange stripe down each side and two spots on its tail. The fully grown caterpillar has four distinctive fair-coloured tufts of hair on its back and is about 30 millimetres long.

Flightless female moth

Fully grown caterpillar

Male Moth

Winged Female Moth

The male moth is generally grey/black, but can be lighter, with one white spot on each wing. It is about 13mm from tip to toe. The female is generally a creamy white colour with a dark spot on the wings, and is bigger.

What to do if you find one

Call the Forest Health on 0800 765 000 to report any possible sightings of tussock moth eggs or caterpillars.

Don't try to remove the eggs - these are very tough and the hairy cocoon on which they are usually laid can cause skin irritations.

If you think you have found a caterpillar, keep hold of the specimen in a closed jar or container. Try not to handle it as contact causes an allergic reaction in some people.

For more information please call
Exotic Disease and Pest Emergency Hotline - 0800 809 966

Page last updated: 30 April 2008