Should you be worried about killer caterpillars?

Should you be worried about killer caterpillars?

We recently received a number of questions about venomous caterpillars. This is probably because of recent reports and sightings of fuzzy tussock moth caterpillars. Let’s take a deeper look at these mysterious insects and try to expel some common myths.

Poisonous vs. venomous:

A poisonous organism (or substance) is one that will harm you if you eat, inhale or touch it because of a toxin it contains. A venomous organism is one that actively injects a toxin through a bite or sting. Most of the poisonous organisms that you’ll likely encounter in Ontario are plants or mushrooms.

Four species of stinging caterpillars found in Ontario: (a) buck moth, Hemileuca maia; (b) Io moth, Automeris io; (c) spiny oak slug, Euclea delphinii; and (d) crowned slug, Isa textula. Photos courtesy of

Caterpillars in Ontario that can cause a human harm fall into two categories: localized stings and allergic reaction or irritation to the skin. Caterpillars that cause localized stings are fleshy, not fuzzy or hairy. They have branched spines coming out from several points along their bodies and spines connected to venom glands. The list of stinging caterpillars in Ontario includes some (but not all) species from the families Saturniidae (giant silkworm moths) and Limacodidae (slug caterpillars). Some people describe the feeling of touching these spines as similar to a bee sting.

Four species of caterpillars in Ontario that may cause dermatitis: (e) gypsy moth, Lymantria dispar; (f) whitemarked tussock moth, Orgyia leucostigma; (g) hickory tussock moth, Lophocampa caryae; and, (h) spotted tussock moth, Lophocampa maculata. Photos courtesy of

Caterpillars that cause allergic reaction or irritation to the skin are very hairy and are from the families Lymantriidae (tussock moths) and Arctiidae (tiger and wasp moths). Their hairs are connected to or contain venom glands and break off very easily. These hairs can get stuck in your skin and cause itchiness and inflammation, or even be inhaled and cause irritation in your airways. Different people may have different levels of sensitivity to these caterpillars.

Here are safety tips to keep in mind when encountering caterpillars:

  1. Don’t touch spiny, spiky or hairy bugs, or bugs with bright colours. Animals often use these signals to indicate that they’re not tasty or can do you harm. Some are faking but if you don’t know, don’t risk it.
  2. Don’t eat caterpillars or pupae.
  3. Teach your children points 1 and 2 above, and also that there are safe ways to pick up bugs (like picking up the twig, leaf, etc. that they’re sitting on, holding them in the palm of their hand without squeezing, not petting them, etc.). Most caterpillar-related medical reports involve children so this is important.
  4. If you or your child is exposed to one of these caterpillars, don’t panic. The poisonous caterpillars that we have in Ontario may cause temporary discomfort but they won’t cause serious harm.

If you do come in contact with one of these caterpillars, remember:

  • First aid for both types of caterpillar injuries is the same.
  • Wash the affected area with soap and water to remove any loose spines or hairs.
  • Dry with air, not a towel.
  • Use tape to remove any remaining spines or hairs.
  • Treat with rubbing alcohol and apply ice.
  • Treat with antihistamines or pain killers as needed.

Insects are an important part of a healthy watershed. Learn what to plant in your garden to attract butterflies, moths and bees here.

2 Comment
  • Elsie Dales says:

    Thank you for sharing. Interesting information.

  • Melanie says:

    Thanks for taking the time to prepare and post this well-written article. You cleared up some questions I’ve had since childhood about touching caterpillars. Now I can pass on the information to my curious kids!

Leave a Comment