This orifice allows the flea to breathe, defecate, mate and expel eggs while feeding from blood vessels. It lives in the cutaneous and subcutaneous dermal layer. Tungiasis lesions almost always occur on the feet (97%), but may occur on any part of the body. The toes are afflicted over 70% of the time, with periungual folds (around the toenail) a preferred site. Only once the female burrows into the skin can reproduction occur, as the male and female show no interest in each other in the wild. The male flea dies after copulation. The female flea continues "in vivo" development, described in stages by the Fortaleza classification of tungiasis. Over the next two weeks, its abdomen swells with up to several hundred to a thousand eggs, which it releases through the caudal orifice to fall to the ground when ready to hatch. The flea then dies and is often the cause of infection as the body rots under the thick scales its body chemistry created to protect it. The eggs mature into adult fleas within three to four weeks and the process begins anew. In a seminal paper on the biology and pathology of "Tunga penetrans", Eisele "et al." (2003) provided and detailed the five stages of tungiasis, thereby detailing the "in vivo" development of the female chigoe flea for the first time. In dividing the natural history of the disease, the Fortaleza Classification formally describes the last part of the female flea's life cycle where it burrows into its host's skin, expels eggs, and dies. Stage 1 is characterized by the penetration of the skin by the female chigoe flea. Running along the body, the female uses its posterior legs to push its body upward by an angle between 45–90 degrees. Penetration then starts, beginning with the proboscis going through the epidermis. By stage 2 (days 1–2), penetration is complete and the flea has burrowed most of its body into the skin. Only the anus, the copulatory organs, and four rear air holes in fleas called stigmata remain on the outside of the epidermis. The anus will excrete feces that is thought to attract male fleas for mating, described in a later section. The hypertrophic zone between tergites 2 and 3 in the abdominal region begins to expand a day or two after penetration and takes the appearance of a life belt.