Img 1 Cat flea larva under a microscope. It has a translucent white body, yellow head, and red gut from consuming fecal blood.
Cat flea larvae are white with a red digestive track Img 1. After hatching from its egg, a larva is a semi-transparent white to off-white color. However, soon it’ll eat adult flea feces, which consists of blood, and its gut turns a dark red color. The crimson color becomes visible through the translucent cuticle, giving the whole larva a darker, brownish appearance.
Newly hatched flea larvae have semi-transparent bodies, white colored bodies. The larval head is distinct from the rest of the body. It has a slightly darker yellow or brown color.
The primary food source of flea larvae is dried fecal blood (flea dirt) from adult fleas. As a larva feeds on the feces, its digestive tract will turn a dark ruby-red to purple color. The red gut is easily seen through the translucent body, and it causes the whole larva to appear a darker color.
Vid 1 How flea larvae appear to the unaided human eye.
Mature third instar larvae prepare to pupate by shedding and defecating out their alimentary canal (gut) contents. As a result of voiding their red guts, the larvae return to a solid white color. Due to their milky white appearance, mature larvae are sometimes called clear-gut larvae.