Paederus dermatitis is a perculiar irritant contact dermatitis characterised by erythemato-bullous lesions of sudden onset on exposed areas of the body. The disease is provoked by an insect belonging to genusPaederus. This beetle does not bite or sting, but accidental brushing against or crushing the beetle over the skin provokes the release of its coelomic fluid which contains paederin, a potent vesicant agent. Due to the pathogenic mechanism, the morphology and location of the dermatitis change from case to case. The lesion usually resembles the accidental dropping of a caustic or hot liquid. The uncommon association of acute dermatitis with minimal or no complaints, which would be noteworthy in the case of chemical or thermal burns, facilitates diagnosis which is corroborated by the season and by the case history.