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Paedarus dermatitis

Author: Maham Ghani, Medical Student, CUNY School of Medicine, New York City, New York, United States. DermNet New Zealand Editor in Chief: Adjunct A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. October 2019.

What is paedarus dermatitis?

Paedarus dermatitis is a skin irritation due to contact with certain species of the rove beetle, such as the Nairobi fly. It is also known as rove beetle rash, dermatitis linearis, spider lick, night burn, and Nairobi fly rash.

A blistering rash occurs 24–48 hours after brushing against or crushing the beetle against the skin, and can take several weeks to disappear [1,2]. 

Paedarus dermatitis

Who gets paedarus dermatitis?

At least 60,000 different species of rove beetle have been identified — the largest group of insects worldwide. These insects are of the family Staphylinidae, in the order Coleoptera (beetles) [2,3]. The beetles have narrow bodies, ranging from 0.5–1.5 cm [4]. They tend to have a shiny black head and thorax, with blue or black elytra (forewing), and an orange-red abdomen [1,4].

Rove beetles can be found in decaying vegetable and animal matter in most environments around the world, except Antarctica [4]. There are more than 1000 different species of rove beetle in New Zealand. They are more prevalent in warmer climates [5]. The beetle breeding period is during the rainy seasons, typically between March and April or July and August [1,4].

Paedarus dermatitis is due to contact with one of more than 622 paedarus species of rove beetle, which have a blistering agent in their haemolymph (haemolymph is analogous to blood in vertebrates).

Outbreaks of paedarus dermatitis are most commonly reported in Europe and Asia, but outbreaks have occurred in many other countries including:

  • Australia
  • Malaysia
  • Sri Lanka
  • Kenya
  • Iran
  • Central Africa
  • Uganda
  • Okinawa
  • Sierra Leone
  • Argentina
  • Brazil
  • France
  • Venezuela
  • Ecuador
  • India [2,5].

The beetle is attracted to ultraviolet radiation (UVR); epidemics have been reported in warm regions with military units and hospital wards with open windows and fluorescent lights [4].

Paederus beetle

What causes paedarus dermatitis?

Paedarus dermatitis is due to pederin, a toxin produced by pseudomonas bacteria in the haemolymph and released by the female paedarus beetle [2,4,7]. Pederin causes a release of epidermal proteases and a loss of intercellular connection, inhibiting protein synthesis, DNA synthesis, and mitosis [2,5].

What are the clinical features of paedarus dermatitis?

A localised streaky or linear erythema arises 24–48 hours after contact with the beetle and is typically followed by vesicles and pustules after 2–4 days [2,4,8]. Symptoms take a week or more to disappear [2]

The cutaneous features of paedarus dermatitis include:

  • Erythema [1,4]
  • Vesicles and pustules [4,8]
  • A burning sensation [1,4–8]
  • ‘Kissing lesions’ where two adjacent flexural surfaces come together [1,4]
  • Periocular dermatitis and keratoconjunctivitus (‘Nairobi eye’) [1,2,4,8]
  • Balanitis (inflammation of the glans of the penis) [1,2].

What are the complications of paedarus dermatitis?

The primary complication of paedarus dermatitis is the pain associated with the rash. Secondary complications include:

  • Infection
  • Exfoliation and ulceration (sometimes requiring hospitalisation)
  • Postinflammatory hyperpigmentation
  • Scarring [2,5].

How is paedarus dermatitis diagnosed?

Paedarus dermatitis is diagnosed clinically.

  • A skin biopsy of an early lesion shows neutrophilic spongiosis, vesiculation, and reticular necrosis of the epidermis [4]. The inflammatory infiltrate in the epidermis contains many neutrophils [4,8].
  • Later biopsies show irregular acanthosis, pallor of superficial keratinocytes, overlying parakeratosis, confluent epidermal necrosis, and suprabasal acantholysis [7,8].

What is the differential diagnosis for paedarus dermatitis?

Paedarus dermatitis may be confused with:

The distinguishing features of paedarus dermatitis include [1]:

  • Irritation confined to exposed areas
  • Kissing lesions
  • Occurrence during rainy/warm season
  • Other individuals presenting with similar lesions
  • Histopathology.

What is the treatment for paedarus dermatitis?

Once symptoms have appeared, the initial step should be to wash the affected area with soap and clean water in an effort to remove the pederin toxin.

After cleaning the area, apply a cold wet compress and a topical steroid [1].

How can paedarus dermatitis be prevented?

Paedarus dermatitis can be prevented by limiting the chance of exposure to the rove beetle.

  • Use insect-proof netting at night.
  • Select light sources that do not emit UV.
  • Turn lights off when sleeping.
  • Remove any beetle found on the skin without crushing it.
  • Wash skin in contact with a rove beetle with soap and water [4,5,7].

What is the outcome for paedarus dermatitis?

It can take a few weeks for paedarus dermatitis to resolve, and postinflammatory pigmentation may persist for several months [1,2].

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Related information



  1. Nasir S, Akram W, Khan RR, Arshad M, Nasir I. Paederus beetles: the agent of human dermatitis. J Venom Anim Toxins Incl Trop Dis 2015; 21: 5. DOI: 10.1186/s40409-015-0004-0. PubMed
  2. Asgar A, Sujitha K, Sivasankaran M, et al. Study on Paederus Dermatitis Outbreak in a Suburban Teaching Research Hospital, Kanchipuram, India. Medicine Science 2013; 2: 764–9. 2013. Available at: [accessed 14 October 2019]
  3. Coondoo A, Nandy J. Paederus dermatitis: An outbreak, increasing incidence or changing seasonal pattern? Indian J Dermatol 2013; 58: 410. PubMed
  4. Elston D.M. Bites and Stings. In: Dermatology 4e 2018 85, 1516–35.
  5. Karthikeyan K, Kumar A. Paederus dermatitis. Indian J Dermatol Venereol Leprol 2017; 83: 424–31. PubMed
  6. Singh G, Yousuf Ali S. Paederus dermatitis. Indian J Dermatol Venereol Leprol 2007; 73: 13–5. PubMed
  7. Mammino J. Paederus dermatitis: an outbreak on a medical mission boat in the Amazon. J Clin Aesthet Dermatol 2011; 4: 44–6. PubMed
  8. Patterson J.W. The Spongiotic Reaction Pattern. In: Weedon’s Skin Pathology 4e 2015: 5, 103–134.e14.

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