Does the IO Moth Caterpillar Really Sting?

Knowledge is a funny thing- you think you know things but often the information comes from books, the internet or other people and you do not have personal experience to confirm a fact.

Recently during an interesting presentation on local moths, the subject came up of whether IO caterpillars sting. Based on information in books such as Wagner’s “Caterpillars of Eastern North America” page 238, I had assumed that their spines can deliver a painful sting. But I had never experienced this in person. So it was a strange coincidence that after cutting some 8 foot tall weeds in a field with my tractor recently, I felt something crawling on my neck and whacked it with my hand. Unfortunately the thing on my neck was the IO caterpillar shown in the attached photo. The result was a painful sting on my neck which did not however last long. I did not feel any stinging in my fingers when I picked the cat off my neck. The intensity of the sting is likely related to how hard the caterpillar is squeezed and how many spines are embedded in the skin and how deeply they penetrate.

The coloration of the IO cat is interesting- it is mostly green which seems an obvious type of camouflage. Then there is a bright red line bordered by white along the sides; this would seem to be a warning coloration yet it is not a very obvious sign of toxicity. The numerous spines with which the caterpillar are covered certainly are intimidating.

So beware of the IO caterpillar- it is painful but compared to some other insect stings, such as that of the yellow jacket wasp, the honeybee, or even the nettle plant, it seems relatively mild in my experience. If you have an allergy to the toxin that would be a wholly different situation and much more dangerous.