Parasite Morphology
The adult female mite, the stage most commonly seen, can be up to 4mm long. The adult male (that dies following copulation) is considerably smaller. Females do not have a distinct head, but oftentimes the mouth parts on the anterior side are misinterpreted as the head. Scabies mites have four pairs of legs; the front two pairs end in "suckers" (that assist in walking), while the hind two pairs end in long bristles that trail behind the body. The female is round, which allows her ovaries and developing eggs to occupy the majority of her body's volume. (Orkin 8)
Adult female scabies mite
The female possesses many anatomical adaptations that enable her to burrow beneath the host's skin. The numerous legs allow the mite to cover relatively large distances quickly (2.5 cm per minute). The front four legs have sharp blades on the "elbows", which are used to both submerge the mite underneath the skin (an hour-long process) and to dig through the stratum corneum. The female mite will continue to dig until she reaches the boundary between the stratum corneum and the stratum granulosum, where she will remain to feed. Once she has burrowed under the human host's epithelium, the female mite will remain there for the remainder of her life.
A) Adult mite; B) Larva; C) Egg containing developing embryo
Copulation takes place when a transient male comes into contact with a female mite that has been waiting in her burrow. After the female has been fertilized for the first time, she will remain fertile for the rest of her life. The female scabies mite lays her first eggs within hours. Eggs tend to be roughly 2mm in length, or just over half of the female's length. From then on out, the female mite will lay 2 to 3 eggs daily. The eggs stick to the burrow surface throughout the incubation period of 3 to 4 days. Observations indicate that just under 10% of all eggs laid survive to adulthood, even when circumstances are favorable.
Scabies egg