Flea larvae develop through three stages of varying duration, where they take the form of first, second, and third instars.. To reiterate, the stages are called stages, and the physical forms of the larvae are called instars.
Stages & Instars
Cat flea larvae develop through distinct three stages. At each respective stage, the larvae are referred to as first, second, or third instars.. To clarify, the stages are called stages, and the physical larval forms are called instars. The stage durations vary, but each stage lasts progressively longer as the larvae become older. The three larval stages are sometimes denoted as L1, L2, and L3.
Img 1 Illustration of a cat flea larva passing through 3 instars as it develops from egg to cocoon.
Molting & Growth
Flea larvae molt twice, once between each of their three stages. Through the process of ecdysis (molting), the larvae are able to shed their outer cuticle to allow for growth. As a result, each larval instar is progressively larger than the last. However, all three instars look alike and are structurally similar. Apart from an increase in size, there is no clear-cut way to differentiate between the instars.