Crayfishes are born from fertilized eggs, which are extruded by a gravid female and subsequently attached to the swimmerettes (pleopods) on her abdomen. This process occurs during the spring months, usually between March and June (Taylor et al., 2015), in most North American crayfishes. The fertilized eggs usually hatch within a few days of oviposition, although the newly-hatched, juvenile crayfish stay attached to their mother for a few more days in order to increase their body size. Once large enough, the juvenile crayfish detach from their mother’s abdomen and become functional, free-living individuals. Juvenile crayfishes spend the warm summer months foraging for food in order to grow as much as possible before food becomes limited during the cooler fall and winter months. Juvenile crayfishes grow rapidly during their first few months of life, and as a result, they molt frequently during this period.
All crayfishes have a calcified exoskeleton that is somewhat hard and inhibits their growth. Therefore, they will periodically exude this exoskeleton in order to grow more rapidly. Freshly molted crayfishes are quite soft (and vulnerable to predation), but this allows them to grow quickly before their new exoskeleton calcifies. Juvenile crayfishes are often recruited to the adult population the following spring, although there is evidence in some species that individuals can become reproductively active at the end of their first summer (Pflieger, 1996). Once adulthood is reached, molting usually only occurs once or twice each year in most North American species (Taylor et al., 2015).
The timing of the adult molt cycle often corresponds to the annual reproductive cycle. Male crayfishes in the family Cambaridae (most North American crayfishes) exhibit cyclic dimorphism with respect to their reproductive morphology. Most notably, the gonopods (sperm transfer organs) alternate between a reproductive (late fall-early spring) and a non-reproductive (late spring-early fall) form, with the reproductive forms often much more slender and with more pointed tips. Males in this reproductive state are often referred to as ‘form I’, and such specimens are often the basis of taxonomic identifications. There is also some evidence to suggest that female Cambarid crayfishes exhibit similar patterns of cyclic dimorphism, with respect to the width of their abdomen (wider in reproductive females) and the presence of glair, the glue-like substance used to adhere fertilized eggs to the abdomen (Wetzel, 2002).
Copulation occurs during the fall and winter months in many species (Taylor et al., 2015), while the summer months may be primarily used for foraging and growing. Most crayfish species in the Great Lakes and the broader Midwest region are thought to live approximately 2-3 years (Taylor et al., 2015). However, some species, such as those in the genus Cambarellus, may live for less than a year, while others, such as those in the genus Cambarus, may live closer to five or more years (DiStefano et al., 2016).