Sometimes the sexually immature adult stages are called L5's In most species sexual reproduction by adult nematodes is the norm and occurs within an infected definitive host. Eggs are laid by the female and pass from this host into the external environment. In the vast majority of nematode life cycles the stage that passes from the definitive host is not the same stage that is infective for another definitive host. A first stage larva develops inside an egg, then hatches. Initiation of the hatching process is controlled by several factors including temperature and moisture levels in the external environment.
Hatching occurs only when environmental conditions are favorable for survival of hatched larvae.
These conditions stimulate the enclosed larvae to assume its own role in hatching by secreting enzymes to digest the surrounding egg membranes, then exerting pressure against the weakened membranes to rupture them and escape. This newly hatched L1 feeds on bacteria and grows until constrained by its outer skin or cuticle. At this point further growth is possible only if the larva grows a new, more flexible, cuticle and casts off its old outer cuticle. This process is called molting and involves two steps. Synthesis of a new cuticle by the hypodermis.