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Lepidoptera (moths and butterflies) contain several species of caterpillars that are armed with stinging hairs and/or fragile spines. These modified hairs serve as an effective means of protection against predators interested in the soft bodied caterpillars. Skin contact with these specially equipped caterpillars can produce severe irritation and inflammation which is often referred to as lepidopterism.
The body surface of various urticating (irritating) caterpillars are adorned with microscopic dart hairs, or rigid bristles, or long and flexible tapering hairs. Hairs may be arranged in a pattern or tubercle on the side or dorsal surface of the caterpillar, depending on the species. The location and structure of the hairs, or group of hairs on the insect, can be used as a diagnostic tool to identify the species of caterpillar.
Urticating hairs can be of two distinct types. The first are envenomating hairs, which are tubular or porous spines capable of holding a venom or irritant produced by a gland at the base. On contact, the tips of the hair break under pressure and release their fluid contents, which is generally a mixture of histamines. There are only two families of lepidoptera within Australia that have caterpillars which possess these stinging hairs; they are the Limacodidae ("cup moths" or "Chinese junk" caterpillars) and the Nolidae (gumleaf skeletonisers). Other hair types on caterpillars are referred to as non-envenomating hairs and these produce a mechanical irritation on contact. These hairs are fragile and easily dislodged from the caterpillar, they adhere to the surface of skin when the caterpiller is contacted, or they become airborne and on settling the barbed or dart hairs easily fragment and penetrate clothing or skin.
Hairs that are air-borne can drift and settle on nearby washing or other surfaces which humans will contact. Accidental disturbance or handling of old larval skins and spent cocoons, deposited under leaf litter, bark, wood piles, timber or any other material that caterpillars have had contact with, can result in irritation. These hairs retain their urticating properties long after the caterpillars have pupated. The families of Lepidoptera that contain these special hairs include, the Arctiidae (tiger moths), Anthelidae (white stemmed gum moth), Eupterotidae (bag shelter moths), Lymantriidae, the tussock moths (mistletoe brown-tail moth and the white cedar moth) and Notodontidae (bag shelter moth and processionary caterpillars).
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