Caterpillars have two types of hair: urticating and stinging. Urticating hairs are itchy, non-venomous and can cause localized dermatitis by mechanical irritation or foreign body reaction. Stinging hairs are hollow spines with poison-secreting cells at the base that cause local or systemic effects after they enter the skin and break off.
With dermal exposures rashes, pain, pruritus, erythema and edema are possible. However, because of an animal's coat, such dermal reactions are not very likely. Oral exposures, while not common, are definitely possible and may lead to drooling, head shaking, pawing due to discomfort, gastritis, esophagitis, difficulty swallowing, enteritis and tongue, lip and oral irritation.
Treatment for a pet exposed to a caterpillar is largely symptomatic and supportive. Rinsing the pet’s mouth out, cold compresses, pain relievers such as NSAIDS may be considered, but tramadol or local anesthetics may be needed in severe cases. Antihistamines and corticosteroids may also be used.
If hairs are present in the skin, they may be removed using tape.
Allergic or hypersensitivity reactions are possible and should be treated by removal of the hairs, antihistamines and possibly corticosteroids.
Ocular exposures are possible but rare, and hairs may be difficult to remove. The first step is to thoroughly flush the pet’s eyes. If signs persist, closer examination by an ophthalmologist may be needed.