Crayfish

Crayfish usually mate in the fall. Females excrete pheromones which are detected by the antennules of males. The openings of the sex organs are located on the front end of the abdomen just below the thorax. In the male, the first two pairs of abdominal pleopods are used as organs of sperm transfer. Using his first set of pleopods, the male deposits sperm into a sac on the female's abdomen. The female stays well hidden as ovulation draws near, lavishly grooming her abdominal pleopods which will eventually secure her eggs and hatchlings to her abdomen. Strenuous abdominal contractions signal the onset of egg extrusion. Cupping her abdomen, the female crayfish collects her eggs as they are laid (they can number 400 or more), securing them with her pleopods, fastidiously cleaning them with thoracic appendages, and discarding any diseased eggs.

Young crayfish hatchlings emerge from the eggs in the spring, and closely resemble adult crayfish in form (although much smaller). The hatchlings cling tightly to their mother's pleopods, eventually taking short foraging forays and scurrying back for protection at the slightest disturbance. During this time, the mother remains relatively inactive and is extremely aggressive in protecting her young from other, non-maternal crayfish, which would cannibalize the young. The mother and young communicate chemically via pheromones; however, the young cannot differentiate between their own mother and another maternal female.