The difficulty that hungry blood-sucking insects have in locating their next blood meal depends upon the closeness of their association with the host. At one extreme we have the permanent ectoparasites which are in the happy position of having food continually ‘on tap’. Only by accident will they find themselves more than a few millimetres from the skin of the host and the blood that it holds. At the other extreme are those temporary ectoparasites, such as blackflies and tabanids, that do not remain permanently in the vicinity of the host. When these insects are hungry their first problem is to locate the host, often a difficult and complex behavioural task. These differences in lifestyle are reflected in the number of antennal receptors different types of blood-sucking insect possess (Chapman, 1982). Not surprisingly the more independent, host-seeking insects possess the most receptors. Thus, lice have only 10 to 20 antennal receptors and fleas about 50, but the stablefly, which spends most of its time at some distance from the host, has nearly 5000 antennal receptors. Considering two bugs, we see that Cimex lectularius has only 56 antennal receptors compared to 2900 on the more adventurous Triatoma infestans.

The level of reliance on blood is also an important factor in host location. So for obligate haematophages such as the tsetse fly and triatomine bugs regular host location is absolutely essential.