Paederus dermatitis is caused when a pederin-containing beetle is crushed, even partially, against the skin. This skin irritation is also called "dermatitis linearis" or "linear dermatitis" because one can inadvertently drag a beetle across the skin in a more-or-less straight line when trying to brush it away. The resulting inflammation will also be linear. Because Paederus species are widely dispersed around the world, this syndrome has many different local nicknames including "whiplash dermatitis", "spider lick", and "Nairobi fly dermatitis". In East Africa, conjunctivitis from getting pederin in the eye is called "Nairobi eye".
Once pederin is on the skin from the initial beetle contact, it may also be spread elsewhere on the skin. "Kissing" or "mirror-image" lesions where two skin areas come in contact (for example, the elbow flexure) are often seen. Washing the hands and skin with soap and water is strongly recommended, if contact with a rove beetle has occurred.
Initial skin contact with pederin shows no immediate result. Within 12–36 hours, however, a reddish rash (erythema) appears, which develops into blisters. Irritation, including crusting and scaling, may last from two to three weeks.From Wikipedia http://en.wikipedia.org/wiki/Paederus