"T. penetrans" eggs, on average, are 604 μm long, The larva will hatch from the egg within one to six days, assuming the environmental conditions (e.g., moisture, humidity, etc.) are favorable. After hatching, the flea will progress through two instar phases. This is unique in that most fleas go through three, instead. Over the course of that development, the flea will first decrease in size from its just-hatched size of 1,500 μm to 1,150 μm (first instar) before growing to 2,900 μm (second instar).