Most of the differences between male and female crayfish are relative differences: females are smaller overall, with smaller chelipeds (claws), wider tails, and larger swimmerets. Females also lack hooks on their 2nd pair of walking legs and have a single circular orifice at the base of the cephalothorax, called a gonopore. Mating occurs in the fall, but the eggs are not immediately fertilized. Instead, after mating with one or more males, the female will store the sperm through the winter in a spermatheca. When she releases the unfertilized eggs in the spring, she’ll simultaneously secrete a substance, called glair, that breaks down the sperm plug that has encased and protected the sperm throughout the long winter. The now fertilized eggs are held in place on her tail.
After hatching, the larvae also stay attached to her tail. Her wider tail and larger, stronger swimmerets help create a safe and secure environment for the young crayfish, protecting for the next few weeks before dispersing. But there’s always a risk that the young will get knocked free of their mother’s tail. Fortunately, adult females secret a hormone that larvae can detect. If displaced the larvae will swim back towards their mom.