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Hairy caterpillars: Pretty, but beware!

Acronicta americana
Credit: Espace pour la vie
Acronicta americana
Hairy caterpillars: Pretty, but beware!

Since late summer, the Montréal Insectarium team has received many requests for information about the arrival of a European caterpillar: the pine processionary (Thaumetopoea pityocampa). It even made the headlines a few days ago as it has been blamed for causing some serious health problems in babies who had put them in their mouth. However, these caterpillars have not yet been observed in Québec, nor anywhere in North America.

Specialists from the Insectarium would therefore like to set the record straight about the pine processionary and a few of Québec’s native caterpillars, which can trigger significant allergic reactions in some people if they touch them or put them in their mouth.

In general, although the vast majority of caterpillars are harmless, those that are hairy or brightly coloured should not be handled unless you know what they are and that they pose no danger.

Defence against predators

To avoid being eaten, some caterpillars are toxic—their hairs contain chemical compounds that make predators sick. They can also spit (regurgitate) or secrete various acids from a gland on their neck. Some of them sting.

Stinging caterpillars’ bodies are covered in tufts of hair that contain chemical compounds. These hairs are very fragile and therefore break easily, releasing these chemicals. When they come into contact with our skin, they can trigger a range of reactions, from a slight stinging sensation to an intense attack of hives lasting several hours—and even more in extreme cases.

Toxic to varying degrees

These chemical compounds act when the caterpillar is eaten; consequently, the toxins contained in the hairs are even more powerful if they come into contact with mucous. Putting one of these caterpillars in your mouth, or inhaling some of its hairs, would expose you to even more severe reactions.

On the other hand, there are hairy and brightly coloured caterpillars that are completely harmless, but imitate species that predators know to sting or be toxic.

Here are a few examples of stinging caterpillars native to Québec: Automeris io, Acronicta americana (American dagger moth), Euclea delphinii, Isa textula, Adoneta spinuloides, Lophocampa maculata (spotted halisidota) and Lophocampa caryae (hickory halisidota) in the Arctiidae family.

Other species are not renowned for triggering allergic reactions, but more sensitive people may develop some skin irritation or respiratory symptoms; the easily recognizable black and rust-coloured “woolly bear caterpillar” Pyrrharctia isabella is one of these.

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