Blister (rove, vesicant) beetles produce chemical irritants which are used for defense. Beetles of the genus Paedrus secrete the toxic chemical pederin which can cause a contact dermatitis in the evening or at night in tropical countries.
Synonyms: Spanish fly, Nairobi eye
Order: Coleoptera (beetles)
Blister beetles include:
(1) Paederus (may be referred to as “Nairobi fly” in Africa)
(2) Meloidae (Cantharidae): includes Epicauta, Lytta (Spanish fly), Mylabris (Chinese blister beetle)
(3) Oedemeridae
Distribution: worldwide, especially in tropical countries
Chemicals involved: cathardin, pederin
Risk factors:
(1) The beetles are attracted to light bulbs or other light sources.
(2) Exposures are most often in the summer but may also occur in the autumn (peak insect numbers; time of maximum skin exposure; longest time spent outside in the evening).
Clinical features of Paederus dermatitis:
(1) sudden onset of a stinging, burning sensation, often at night ("night burn")
(2) may give a history of brushing an insect away from the site shortly before the onset
(3) vesicles, bullae and small pustules on an erythematous base
(4) present on uncovered parts of the body, usually on the face, neck and upper extremities
(5) may occur as a "kissing" lesion (symmetrical about a flexural site)
(6) nonlinear and nondermatomal distribution
(7) no signs of a bite or puncture site
Laboratory features:
(1) Cultures for bacteria and viruses are negative.
Differential diagnosis:
(1) impetigo (positive bacterial culture)
(2) herpes zoster (dermatomal distribution and/or positive viral culture)
(3) insect bite or sting
