It is a common misconception that lobsters find a single partner and remain bonded for life. Lobsters are not monogamous, and the idea of a lifelong pair is not supported by their biology. Their reproductive strategy involves a temporary, tactical bond related to the female’s molting cycle. This short-term pairing is ritualized, centered around the female’s need for security during her most vulnerable state. The reproductive commitment is ultimately a solitary, long-term investment made by the female, occurring long after the male has moved on.
Finding a Partner: Pheromones and Courtship
The initial stage of the reproductive cycle is driven by the release of pheromones by the female. When preparing to molt her shell, she releases a stream of urine containing these chemical signals, which are detected by the male’s antennules. This advertisement signals her readiness to mate and often attracts the largest, most dominant male.
The male’s initial reaction to the female is often aggressive, but the pheromone-laced urine stream she directs toward him subdues his hostility and calms him. This ritualized exchange is a form of active courtship that prevents the male from attacking the smaller female. Once the male is receptive, he allows the female to enter his shelter, typically a secure, defensible rocky den.
The Temporary Cohabitation Den
The cohabitation period within the male’s den is the closest the species comes to forming a temporary pair bond. The female seeks out the den of a dominant male because she needs a protected space to undergo molting. Shedding her hard exoskeleton leaves the female in a highly vulnerable, soft-shelled state.
Mating only occurs immediately after she sheds her carapace. The male’s primary function during the week or two of cohabitation is to act as a security guard, defending the den and the soft-shelled female. After the female molts, the male gently turns her onto her back, and mating takes place with the transfer of sperm packets into a receptacle on the female’s underside. The temporary cohabitation ends shortly after the female’s new shell begins to harden, at which point she leaves the den and the male is free to court the next receptive female.
The Female’s Reproductive Commitment
Following the short-lived pairing, the female begins a long, solitary reproductive commitment. The male deposits sperm packets into the seminal receptacle, where the sperm remains viable for a prolonged period. Females can store this sperm for up to 15 months, allowing them to decouple mating from the timing of fertilization and egg laying.
When the female determines that environmental conditions are optimal, she releases her eggs, which are fertilized as they pass over the stored sperm. She secures the fertilized eggs, which can number between 3,000 and 75,000, to the fine hairs on her swimmerets on the underside of her tail. She carries these eggs externally for an incubation period of 9 to 12 months, during which time she is referred to as “berried.”
Molting and the Cycle of Reproduction
The requirement for the female to molt in order to mate is the biological reason permanent pairing is impossible. Lobsters must shed their shells to grow, and the reproductive cycle is linked to this growth process. Since mating can only occur when the female is in her soft, vulnerable state immediately following a molt, she must repeatedly seek out a protective male’s den for each reproductive cycle.
Female lobsters are long-lived and can reproduce many times, molting and mating approximately once every one to two years. The ability to store sperm allows a single mating encounter to fertilize multiple clutches of eggs before the female molts again. This cyclical, non-exclusive mating strategy ensures the female maximizes protection during molting and maintains reproductive flexibility.