Img 1 Cat flea larva under a microscope (1 mm measurement scale on the right).
Newly hatched flea larvae are 2 mm long. When fully grown, they’re 4-5 mm long, and 0.5 mm thick. The larval body is long and slender, like a worm or maggot. Prior to pupating, the body slightly shorten in length.
Larval Instars & Growth
Flea larvae develop through three stages, becoming 1st, 2nd, and 3rd instars. They molt once between each stage. Through this process, the larvae shed their outer cuticle to allow for growth. As a result, each instar is progressively larger in size.
Flea Larvae Size
Flea larvae have thin, worm-like bodies. Upon hatching from eggs, first instars measure about two millimeters in length. When they’re fully grown, third instars are four to five millimeters long, and 0.5 millimeters wide. Before pupation, third instars will slightly shorten in length.
Vid 1 Video of a cat flea larva on a dog bed. See the pointing finger for a size comparison.
For comparison, an average piece of medium grain rice is 5 mm long, a sharpened #2 pencil’s tip is around 1 mm, and dimes have diameters of 17.9 mm. So, while cat flea larvae are very small, they’re still big enough to be seen by the naked eye.
Img 2 Comparison of the size of a cat flea larva to the tip of a sharp #2 pencil.