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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Skin problems due to caterpillars and moths

Background

Moths and butterflies, and their larvae, caterpillars, belong to the order Lepidoptera. Although there are an estimated 125,000 to 150,000 different species in this order, very few are capable of causing adverse reactions in humans. Caterpillars are responsible for the vast majority of adverse reactions. Adult moths are less commonly implicated, and adult butterflies do not appear to be responsible for any adverse reactions in humans.

Bamboo caterpillars, which caused a rash on a gardener Bamboo caterpillars, which caused a rash on a gardener
Images supplied by Tertia Wildy
Bamboo caterpillars, which caused a rash on a gardener

How do caterpillars and moths injure the skin?

How common are skin complaints due to caterpillars and moths?

What are the reactions to caterpillars and moths?

In most cases, adverse reactions to caterpillars and moths are mild and resolve spontaneously. Reactions from contact with caterpillars or moths can be classified based on the predominant symptoms.

Reactions to caterpillars and moths
Type of reaction Clinical features
Localised stinging reaction
  • The majority are caused by caterpillars.
  • In NZ, the gum leaf skeletonizer sting can cause pain, redness, and weal formation (swollen small red bumps or large flat areas).
  • Internationally stings from other caterpillar species can cause varying degrees of pain, itchiness, weal or blister formation, and rarely systemic symptoms such as dizziness, sweating, and abdominal pain.
  • The most severe sting is from the puss caterpillar from the US and Central America. Severe pain occurs in all patients, and 1 in 3 develop systemic reactions such as headache, muscle spasms, breathing difficulty, and convulsions.
Papular urticaria and dermatitis
  • Usually caused by hairs from caterpillars or moths.
  • Reactions range from mildly itchy, papular urticaria (small red bumps and swelling) that resolves within an hour; to moderately itchy, urticarial, scaly, blistering, or widespread eczema-like reactions that can persist for weeks.
  • No Lepidoptera species in NZ cause this type of reaction.
Urticarial weals
  • Three species of caterpillars cause urticaria or angioedema. These species are all from the genus Thaumetopoea and are not found in NZ.
  • Appears to be due to an allergic reaction.
  • Systemic symptoms such as vomiting, abdominal pain, or anaphylaxis are rare.
Widespread haemorrhage (bleeding)
  • Some species of Lonomia caterpillars, found in South America, cause localised stings that may progress to a severe haemorrhagic illness.
  • The sting transmits venom which causes burning pain, headache, nausea, or vomiting.
  • Over the next few days widespread bleeding occurs into the skin, mucous membranes, lungs, brain, or kidneys.
  • This can be fatal, but antivenom is available.
Biting moths
  • Symptoms have been described as painless and transient to intensely painful with swelling that persists for up to 24 hours.
  • Biting moths, from the genus Calyptra, are found only in southern and Southeast Asia and eastern Russia.
Ophthalmia nodosa
  • This is a toxic or allergic eye irritation caused by caterpillar hairs.
  • The hairs may be windblown, transferred to the eye with a finger or other object, or the caterpillar may contact the eye directly.
  • Upper eyelid contact dermatitis usually occurs. Immediately after exposure, chemosis (swelling of the conjunctiva) develops. Patients may feel the sensation of a foreign body. Structures in the eye can become inflamed and granulomas (ball-like collections of immune cells) may form. Caterpillar hairs are frequently found within these granulomas.
  • Any hairy caterpillar can cause this reaction.
Oral exposure
  • Rare. Most cases occur in children.
  • Crying, drooling, and lip irritation occurs immediately. Redness, pain, swelling, and itch develop commonly around the tongue and lips. Occasionally the palate, airways, or oesophagus may be affected.
Dendrolimiasis and pararamose
  • These refer to itchy skin rashes associated with joint pain or inflammation. Cartilage may also be involved in dendrolimiasis.
  • Joint destruction and potentially deforming arthritis can result.
  • Caterpillars and moths that cause these conditions are found in China and Brazil.
Hand irritation from contact with caterpillars
Irritation due to contact with caterpillars

How are reactions to caterpillars and moths diagnosed?

A diagnosis of a reaction to a caterpillar or moth is very difficult to make. The clinical features are non-specific and mimic those of many other insect bites, allergic reactions, and dermatological conditions. Features which may make the diagnosis more likely include:

Laboratory tests are generally not helpful.

What is the treatment for reactions to caterpillars and moths?

General first aid measures include:

There is no specific treatment for most caterpillar and moth reactions (the only exception is the widespread haemorrhagic illness due to Lonomia caterpillars, for which there is an antivenom).

Related information

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Author: Marie Hartley, staff writer.

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If you have any concerns with your skin or its treatment, see a dermatologist for advice.