Caterpillar Stings: Venomous Species, Symptoms, and First Aid

Most caterpillars are harmless. A few possess urticating spines/hairs connected to venom glands causing erucism (caterpillar dermatitis).

Notable Venomous Species (North America)

• Puss Caterpillar (Megalopyge opercularis): Most venomous in US. Furry, teardrop-shaped. Hidden spines. Sting: immediate intense burning, radiating pain, lymphadenopathy, nausea, headache, sometimes hypotension, seizures.
• Saddleback Caterpillar (Acharia stimulea): Green with brown saddle. Prominent spines. Pain, swelling, nausea.
• Io Moth Caterpillar (Automeris io): Green with stinging spines.
• Buck Moth, Flannel Moth, Hag Moth caterpillars.

Symptoms

• Local: Intense burning/stinging, erythema, edema, urticaria, papules, vesicles, grid-like hemorrhagic pattern (spine tracks).
• Systemic (moderate-severe): Nausea, vomiting, headache, fever, lymphadenopathy, tachycardia, hypotension, muscle cramps, respiratory distress (rare).
• Ocular: Hairs in eye → conjunctivitis, keratitis (ophthalmic emergency).

First Aid

1. Remove Spines/Hairs: Adhesive tape (duct tape, packing tape) press-peel repeatedly. Do NOT rub—breaks spines, releases more venom.
2. Wash: Soap and water. Gentle.
3. Cold Compress: Ice pack (wrapped) 10 min on/off for pain/swelling.
4. Topical: Hydrocortisone 1% cream, calamine lotion, baking soda paste.
5. Oral: Antihistamine (diphenhydramine, cetirizine) for itch/systemic. NSAID (ibuprofen) for pain/inflammation.
6. Ocular Exposure: Irrigate 15+ min. See ophthalmologist immediately.

When to Seek Medical Care

• Severe pain uncontrolled by OTC meds.
• Systemic symptoms (difficulty breathing, swallowing, widespread hives, dizziness, muscle spasms).
• Eye involvement.
• Known allergy to insect venoms (anaphylaxis risk).
• Symptoms worsening after 24h.

Most stings resolve in hours to days. Pain from puss caterpillar can last 12–24h.