Two monitor lizard species in Senegal (Varanus niloticus Linne, 1766 and Varanus exanthematicus Bosc, 1792) have the same one-host reptile tick, Aponomma flavomaculatum (Lucas, 1846) (Ixodoidea: lxodidae). In both host species adult female ticks attach mainly in covered areas of the legs, especially in the axillae, where there is minimal disturbance with optimal feeding conditions. Adult female density is very low and nonfeeding adult males may have to wait a long time before locating a mate. During this phase the males attach on the host in places where they are protected but can also receive female pheromone signais, eg. in nasal cavities and around the cloacal orifice. Compared with inactive males few adult males in the activity phase of mate searching were found . The immature stages appear to choose those sites which provide optimal feeding with. minimal disturbance. The nymphs are found mainly on the legs and axillae while larvae attach preferentially on the lateral body sites and on the neck, where they are protected under the posterior edges of scales. It is proposed that the most likely reason for change of attachment site in the stages of the tick is interstadial competition. This mechanism seems to be long established in evolutionary terms, because the stages attach on the preferred sites when other stages are absent, or infestation rate is very low.