In the period before spawning, freshwater crayfish develop glair glands on the underside of the pleon. These glands produce the mucus for a tent-like structure in which the eggs are fertilized and attached to the pleopods. Long-term observation of females of slough crayfish, Procambarus fallax, kept in the laboratory without contact to males revealed that glair glands developed in late winter and early autumn of each year. However, in contrast to mated females, unmated females never formed fertilization tents and never spawned. Their glair glands persisted for an unusually long period of time and disappeared only during the next moult. Inhibition of spawning and mucus release from the glair glands suggests that the females had information on sperm availability and saved resources when unmated. Marbled crayfish, Procambarus virginalis, a parthenogenetic descendant of slough crayfish, developed glair glands and spawned in spring and autumn as their mother species although they never mated. These findings suggest that on their way from gonochorism to parthenogenesis regulation of spawning and glair gland activity has been decoupled from mating and sperm transfer.