This, along with genetic differences among the T. penetrans fleas that infect different host animals, may suggest that there are several species of closely related species have been grouped taxonomically under one binomial nomenclature.Though the chigoe flea resembles most others in morphology, the flea has a hypertrophic region between tergites 2 and 3. As stated in Eisele et al. (2003), tergites 2 and 3, as well as the abdominal sternites, stretch considerably and are bent apart. Chitinous clasps that are built for the abdominal enlargement surround these regions and hold onto the hypertrophic zone, giving them the appearance of a three-leafed clover. (See image 7 of the life cycle diagram.) Surprisingly, the rest of the flea, including the head and the thorax, do not change in shape.,With the rapid expansion of the flea, the morphology of the flea is now vastly different. It has gone from the smallest flea in the world to a bulging mass that measures 5–10mm in diameter. This results in a volume that is 2000 to 3000 times what it used to be. Reproduction
Females have a depression or groove at their abdominal end whereas the males have their protrusive copulatory organs in that same region. These morphological differences reflect the way the male and female copulate. In the first step toward copulation, the female penetrates an organism in an ungravid state. It is only there that the male will find her and copulate. Copulation of adults has not been observed in the wild.
With the female reproductive organs pointing outward, the male will place his reproductive organs "in direction to the upright abdominal end of the female" to copulate. Having copulated for only a few seconds to 2 minutes, the male will then begin to search for another female. After copulation is complete, the male will die, although sometimes he will take a blood meal before doing so. Eggs will be expelled whether or not they have been fertilized.The chigoe flea eggs’ average length is 604 μm and the just hatched larvae, in their first instar, have an average length of 1,500 μm. At the second and last instar (T. penetrans is unique among the fleas in that it only has two, instead of three, instars.) the larvae decrease in size to 1,150 μm after growing to at least 2,900 μm. The development from instar 1 to instar 2 lasts less than one day.On the whole, Tunga penetrans does not do very well in terms of its Darwinian fitness. In a laboratory setting in which different mediums were provided for larval growth, the rate of survival from egg to adult in the best medium was 1.05%. Only 15% of the eggs were found to develop into larvae, and of those, only 14% formed a cocoon. Moreover, only half of the pupae reached the adult phase, resulting in gender disequilibrium.