Egg -- Each white, oval-elongate egg is slightly less than 1 mm long and glued to a hair by a relatively large mass of a cement-like substance.
Nymph -- The nymph is smaller than the adult but resembles it in shape.
Hosts -- Man is the only host on which crab lice are known to breed and survive.
Damage -- The crab louse usually infests hair on the pubic area, chest, armpits, and beard. More rarely, the scalp or eyelashes of young children may be infested. While gripping several hairs, the louse pierces the skin with its needle-like mouthparts and sucks blood. This feeding action causes the formation of blue spots 0.2 to 3.0 cm in diameter on the skin. These spots may not appear for several hours after the bite and may last several days.
Reaction to a crab louse infestation varies with the individual. The bits may be only mildly irritating to some persons or cause eczematous skin conditions in others due to constant scratching.
Life History -- All stages of the crab louse may be found during any season of the year. Under experimental conditions, the female has been found to deposit up to 30 eggs at a rate of 3 eggs per day. These eggs are glued to hair and hatch in 7 or 8 days. The nymph which is less active than the adult feeds and develops through 3 instars in 13 to 17 days. The nymph then molts into an adult and the life cycle is repeated. A new generation may be produced every 22 to 27 days.
The crab louse is a very sluggish and slow-moving parasite. Because the crab louse is adapted for clinging to hair, movement in the absence of hair is very difficult. Sexual contact plays a large part in the spread of these insects; however, transmission on objects, such as blankets, used by infested persons commonly occurs.