Moth and butterfly caterpillars can sometimes cause an allergic reaction known as caterpillar dermatitis (lepidopterism). So after human skin comes into contact with the hairs on a caterpillar’s legs, symptoms begin to show up. While I’ve seen frequent cases of caterpillar dermatitis, I’m still not sure about one key aspect: what specific allergen in the hairs causes the dermatitis?
It turns out that, like porcupines, caterpillars have venomous quills. These spines, called verrucae, contain poisonous fluids, and are nestled beneath the leg hairs. When they penetrate skin, these verrucae introduce the venom into the bloodstream. Hence, an allergic reaction ensues. While the venom is usually not life threatening because of the caterpillar’s small size, it’s still irritating.
Caterpillar dermatitis manifests in hives, itching, and rashes, to name a few. Treatment is relatively simple and non-invasive due to the reaction’s topical nature. If you or your child should develop mild caterpillar dermatitis, use topical corticosteroid cream in addition to an oral antihistamine. As a result, the lesions usually heal within one week without scars.
REFERENCES:
Caterpillars: MedlinePlus Medical Encyclopedia. U.S National Library of Medicine. https://www.nlm.nih.gov/medlineplus/ency/article/002860.htm. Published July 14, 2015. Accessed July 7, 2016.
Foot NC. Pathology Of The Dermatitis Caused By Megalopyge Opercularis, A Texan Caterpillar. Journal of Experimental Medicine. 1921;35(5):737-753. doi:10.1084/jem.35.5.737.
Müller CSL, Tilgen W, Pföhler C. Caterpillar dermatitis revisited: lepidopterism after contact with oak processionary caterpillar. BMJ Case Reports. http://www.ncbi.nlm.nih.gov/pmc/articles/pmc3082058/. Published April 20, 2011. Accessed July 7, 2016.