 Sucking lice are small wingless insects ranging from 0 @.@ 5 to 5 mm ( 0 @.@ 02 to 0 @.@ 20 in ) in length . They have narrow heads and oval , flattened bodies . They have no ocelli , and their compound eyes are reduced in size or absent . Their antennae are short with three to five segments , and their mouth parts , which are retractable into their head , are adapted for piercing and sucking . There is a cibarial pump at the start of the gut ; it is powered by muscles attached to the inside of the cuticle of the head . The mouthparts consist of a proboscis which is toothed , and a set of stylets arranged in a cylinder inside the proboscis , contaiing a salivary canal ( ventrally ) and a food canal ( dorsally ) . The thoracic segments are fused , the abdominal segments are separate , and there is a single large claw at the tip of each of the six legs . 
