Locating Blood
Most blood feeders can be put into one of two biting groups; selonophagic or telophagic
Mosquitoes, Triatome Bugs, Ticks (Selenophagic Feeders)
Example Vector: Mosquito. When a mosquito lands on a suitable host it pushes its sharp stylets into the skin in the search of a small capillary, which from a mosquito's point of view, are not everywhere. The relatively tough labial sheaths, fold and stay above the skin surface as chemo-receptors on the end of the stylets try to detect blood. The stylets, made of the labrum and labium (upper and lower lips) have two channels; a relatively large dorsal channel that will conduit blood, and a narrower ventral channel that pumps saliva into the search area. The stylets have recurved "teeth" at their tips that serve to rachet themselves deep into the skin as a result of a back and forth movement of the head. Once blood has been found these teeth act as anchors for the duration of the feeding. Venule canualtion is actually quite rare, and if the mosquito can't find a capillary, it will feed from a haematoma (a blood pool). Haematomas form as a result of the cutting and probing of the stylets through the skin. A cibarial pump in the head moves the blood into the midgut, and stretch receptors there signal the end of feeding. The stylets are forcibly pulled from the skin. The female may not feed again for up to a week if it obtained enough blood to produce a batch of eggs (vitellogenesis). It should be mentioned that triatomes are very deep feeders and, even though they probe and lacerate vessels in search of blood, they actually probe until they can canulate an arteriole or venule to feed (Ribeiro and Garcia, 1981).
Black Flies, Sand Flies, Tsetse Flies (Telophagic Feeders)
Example Vector: Black Fly. Chemoreceptors in the tarsomeres and heat are important cues that initiate probing in black flies. However, their mouthparts are quite short, and breaching the skin surface is accomplished by scissor-like mandibles. In effect, the process is quite unsophisticated when compared to selenophagy; several capillaries are torn and blood wells into the wound (surface haematoma). This blood is pumped into the midgut by the cibarial pump through the labrum and labium which form a short tube.