Deltamethrin (Butox 7.5, Versatrine)-treated hair of cattle and sheep were brought into contact for 15, 30, 60, or 120 s with freshly caught Culicoides specimens, which are the vectors of the Bluetongue virus. The hair was clipped off from the treated animal just above the claws-a region which is one of the predominant biting sites of the midges. Hair obtained on day 7, 14, 21, 28, or 35 after treatment were mingled with the Culicoides specimens for the given contact periods. After separation of the midge from the hair and placing them onto white filter paper in a petri dish, their fate was followed for the next hours by microscopic inspection. It was found that deltamethrin (in both formulations Butox, Versatrine) reaches for 35 days in such sufficient amounts in the hair of the legs to kill attacking specimens of Culicoides in reasonable short periods after very short contacts. The observed speed of kill and the deleting effects were so quick that the midges very probably would not bite before their death.