The sequential histological development of Argas vespertilionis (Acarina: Argasidae) feeding sites on Eptesicus serotinus (Mammalia: Chiroptera) was evaluated. Neutrophils, followed by Langerhans cells, were the major components of the cellular infiltrate throughout the earliest phase of tick infestation. The host tended to isolate the tick mouthparts by means of a progressive formation of epithelial tissue in the feeding cavity.