Caterpillar dermatitis caused by oak processionary moth (Thaumetopoea processionea)

Synonyms: Thaumetopoea processionea

By Dr. Pascal Bafteh · last updated 09/2026

Definition & cause

• Cause: The triggering agent is setae (urticating hairs) from caterpillars of the oak processionary moth (Thaumetopoea processionea).
• Toxin: the seta-bound protein thaumetopoein plus high-molecular-weight allergens — a combined toxic-irritant + IgE-mediated reaction.
• Distribution: widespread in Central and Southern Europe; in Germany expanding since the 1990s, especially Brandenburg, Saxony-Anhalt, North Rhine-Westphalia, Bavaria.
• Season: Main season is May to August (larval stages L3 – L6) — caterpillars from L3 onward AND moulting / nest remnants on the ground stay hazardous into winter.

Clinical picture (triad)

a) **Cutaneous — caterpillar dermatitis

• Hallmark: intensely pruritic erythematous papules / wheals in streaks, typically within the first 8 – 12 h after exposure.
• Predilection: uncovered skin (neck, nape, décolleté, forearms, ankles) — "contact streaks".
• Course: 1 – 2 weeks; persistence due to retained setae (mechanical re-irritation) is possible.

b) **Mucosal & respiratory

• Conjunctivitis with lid swelling and tearing; severe cases keratitis.
• Rhinitis, pharyngitis, bronchial obstruction with cough, dyspnoea — life-threatening in asthmatics.

c) **Systemic (rare)

• Fever, generalised urticaria, dizziness.
• Anaphylaxis with shock is possible, especially with heavy setae load or pre-existing atopy / insect sensitisation.
• Severity grades: As for every immediate-type reaction, grading follows the anaphylaxis grades of Ring and Messmer: I skin/mucosa (urticaria, flush, angioedema), II additionally circulation/airway/abdomen (tachycardia, fall in blood pressure, dyspnoea, nausea), III shock or bronchospasm, IV respiratory/cardiac arrest.

Diagnosis

• Clinical + history: woodland / oak exposure within the last 12 h, streaky pattern on uncovered skin, seasonal context.
• Useful: adhesive-tape sampling → light microscopy of setae.
• Lab: For systemic reactions the rational work-up is tryptase + specific IgE for Thaumetopoea; for respiratory involvement blood gas + spirometry.
• Testing pitfall: Skin tests (prick/intradermal) are not interpretable under antihistamines — observe an adequate washout before testing; tryptase and specific IgE, by contrast, can be taken from blood at any time.
• DDx: insect bites, photoallergic / phototoxic dermatitis, urticaria, allergic contact dermatitis.
• DDx erythema migrans: After time in woodland always also consider a tick bite: erythema migrans is a slowly expanding, annular, usually non-pruritic and non-scaling erythema (scaling points to tinea) — treatment is doxycycline 200 mg for 14 days, but only from the 9th year of life, before that amoxicillin; serology is of little help in stage I (IgM only after 3–6 weeks).

Differential diagnoses

• Airborne contact dermatitis
• Phytophotodermatitis
• Insect bite reaction
• Urticaria
• Urticaria papulosa
• Nummular eczema
• Atopic dermatitis (atopic eczema)

More parasitic skin diseases

• Demodicosis
• Filariasis
• Cutaneous leishmaniasis
• Cutaneous larva migrans
• Pediculosis capitis
• Crusted (Norwegian) scabies
• Scabies
• Tungiasis

Note: This page is intended for medical education and does not replace diagnosis or treatment decisions in individual cases. Treatment and follow-up content is available in the app.