Biochemical characteristics and pathogenic effects of Paederus Fuscipes Curtis are identified by morphological and biochemical markers in patients from northern IRAN. All inspection data from patients, skin lesions, sleep locations, beetle activity, and interviews with directors of the clinical laboratories are documented. The patients were infected by a plague of rove beetles, Paederus fuscipes. The arthropods do not bite or sting but accidental crushing of the beetle on the skin provokes the release of its coelomic fluid which contains paederin, a potent vesicant agent. With Paederus fuscipes, symptoms are mild, disappearing in a few days on develop lesions, which, become full developed with new peripheral vesicles. Biopsy of hand skin demonstrated epidermal atrophy, hyper vascularity and vasodilatation of dermal vessels, and degeneration of dermal connective tissue. The best approach of controlling the paederus infection is to avoid contacting the beetles. Paederus fuscipes needs little treatment. Topical steroids, with antibiotics, if necessary to prevent impetiginisation, may be useful in the acute phase.