Key Points:

Three Auckland girls were stung in a tree by venomous Australian caterpillars that have become widely established here.

It happened in February when the girls, aged around 10, were climbing a eucalyptus tree at their school in Avondale, today's New Zealand Medical Journal reports.

The hairy caterpillar, called the gum leaf skeletoniser, was first discovered in New Zealand in 1992 and is now firmly established throughout the Auckland region, Ministry of Agriculture and Forestry human health adviser Dr Jose Derraik says in the journal.

The long-haired caterpillar, which grows to 25mm in length and develops into a moth, has brown and yellow markings. It eats the leaves of gum trees and closely related plants, although the young caterpillars do not eat the veins, leaving leaves "skeletonised".

Short, stiff, hollow bristles on the caterpillar contain venom that can be injected into skin on contact and even dead caterpillars can cause stings.

In Auckland, the caterpillars are usually present from January to March and from May to October. They are not known to be established outside Auckland, but individuals have been caught in traps at Katikati and Warkworth.

"Due to its wide distribution, eradication was deemed to be not feasible," Dr Derraik says. "[The insect] is now the focus of a long-term management programme aiming particularly at filling current knowledge gaps and controlling the existing population."

The three girls were in "some distress" from the intense itching they experienced.

One had allowed a caterpillar to crawl onto her, before shaking it off. She ended up with welts on the back of her hands and lower arm.

The other two seemed not to have handled the caterpillars but were exposed to them on the tree. One had welts on her ankles, the other had them on the forearm and thigh.

Antihistamine applied to the skin provided some relief and by the following day the girls' itchiness and discomfort had gone.

Dr Derraik said the number of children being exposed to the caterpillars in Auckland was unknown. It appeared to be a rare occurrence, based on the ministry's figures, but there had been at least one previous incident involving kindergarten children in Manukau and several cases on private properties.

The possibility of severe reactions could not be discounted, but in the report he says none had been seen.

"Although exposure may still cause considerable discomfort, the reactions seem to be relatively minor."

Treatment can involve using ice packs, antihistamine tablets or cream - and corticosteroids for inflammation.