“Lepidopterism” refers to various skin & systemic reactions secondary to contact with moth and butterfly larvae or caterpillars (order Lepidoptera). It is worth noting that the adult forms of moths and butterflies do not sting. “Erucism,” taken from the Latin derivation “eruca” (caterpillar) refers to the cutaneous reactions only.

Toxic dermal reactions are commonly due to physical contact with caterpillar's setae (hair or spines). These are hollow structures with a single basal poison gland. These spines fracture and inject venom under pressure. Some species release these toxic setae into the environment where they can be inhaled and affect both the upper and lower respiratory tract. Another source of exposure, direct or aerosolized, is from the caterpillar's hemolymph (invertebrate's blood equivalent).

Toxicologic studies of caterpillar venom are most prevalent in the toxicology & dermatology literature; however, more studies are necessary for complete understanding. From current research, the venom has been found to contain peptides, hyaluronidase, phospholipase A, and bioamines such as histamine (or histamine releasing substances).

Prehospital treatment is as simple as washing the affected areas of skin with soap and water and drying without contacting the skin (such as using a hair dryer or fan).  Remember to remove any constricting clothing or jewelry as soon as possible. 

Consider local cooling measures: gentle application of ice packs and topical isopropyl alcohol.

All suspected ocular exposures should undergo immediate irrigation with copious amounts of water.  Placement of a topical anesthetic will significantly ease eye pain and facilitate treatment/examination.  Consider using a Morgan lens if available.  Analysis with a slit lamp using fluorescein will help to determine if any setae remain on the cornea or if resultant corneal abrasions are present.  Consider urgent ophthalmologic consultation for any caterpillar-related eye exposures.  

For suspected setae exposures, adhesive tape applied to the skin then removed will remove remaining caterpillar spines.  Duct tape is most useful for this approach; however, any available tape will do. 

Cutaneous symptoms are manageable with oral antihistamines and application of topical corticosteroids.  Systemic steroids can be considered in refractory cases or with severe symptoms. 

Supplemental oxygen, antihistamines, and beta-agonist inhalers or nebulizer treatments can control respiratory presentations. 

Patients presenting with anaphylaxis or severe allergic reactions should receive therapy according to standardized treatment algorithms.

Systemic toxicity requires management in a supportive manner (patient monitoring, following baseline renal and coagulation function, intravenous fluids). Emergent consultation with a toxicologist or poison control center can be beneficial in providing treatment algorithms and/or specific recommended treatment.

The best prevention is by assuming all caterpillars are toxic.  Teaching children and outdoor workers avoidance will alleviate most exposures. 

It is essential to have a heightened level of alertness during peak caterpillar seasons (spring/summer), particularly in endemic areas.

Protective clothing like long-sleeved shirts, long pants tucked into socks, work gloves along with a wide-brimmed hat minimizes the likelihood of accidental exposure.

For known areas of heavy infestation or presence of toxic setae, persons in areas where exposure might occur should utilize a tight-fitting respirator mask and eye protection.