The phenomen El Niño that affected Peru at 1998, made possible the growth of copious vegetation in traditionally dry places. On this way, Paederus irritans, dipterous of the order Coleoptera that produces dermatitis when croushed on the skin, found substract that allowed the natural growth of its population. The coming of occasional rains on the months of February to April 1999, attacked the habitat of this insect, that looked for urban areas, exposing seriously the general population of Piura on north Perú to the contact. During February and May 1,451 cases of dermatitis caused by Paederus irritans, called latigazo because of its linear and eritematous characteristic lesions on the skin, were notified at Piura. The more affected body areas were head (56.6%) and neck (30.9%), but there were also cases of conjunctivitis and genital injuries, because of hands contamination.