Lobsters communicate primarily through the use of chemical signals called pheromones. While hormones are chemical signals working inside of bodies "telling" organs to function, pheromones are secreted to the outside and trigger specific responses in members of the same species.

In previous columns, I wrote about how varying the sex ratio within a group had a dramatic impact on the lobster mating system. Interfering with the sense of smell results in similarly aberrant behavior and, again, compromises lobster mating success.

Under normal conditions, a premolt female chooses a dominant male as a mate, moves into his shelter, lives with him during a brief pair bond, mates after molting, and then moves out a few days later.

The female gains at least two advantages from this situation: protection from predation and/or cannibalism during molting; and a replenished sperm supply to fertilize her eggs.

The male benefits by procreating and consuming part of the female molt shell.

The lobster detects odors using chemoreceptors located at the base of the tiny hairs on the antennules, the shorter pair of antennae. Although it may seem odd to think about smelling underwater, scents require a moist medium for sensing. That's why we have moist nostrils.

By removing the antennules, I blocked the female lobsters' ability to smell and they would not move into a male shelter. Molting occurred in the open and females were cannibalized when they molted. Although these females mated, they were not protected by the male. Mating was consequently unsuccessful.

Establishing a pair bond and cohabiting appear to require that the female be able to smell the male. This suggests that a male pheromone triggers appropriate female courtship behavior.

When I blocked the males' ability to smell, the behavioral aberrations were far less dramatic.

Typically, the male stands back and waits patiently while the female molts. It takes a one-pound female about a half-hour to escape from her old shell once she has rolled over on her side. During this time, the male stands at a shelter entrance raised up on the tips of his walking legs fanning his swimmerets incessantly with the tips of his claws pointed downward. This is the typical posture of an excited lobster.

Instead, males that can't smell walked up to their mates while they were shedding and hovered while poking with the pinchers on the second pair of walking legs. The pinchers on the little legs are covered with chemoreceptors that lobsters use for taste. Males lacking the ability to smell seemed to substitute touching and tasting as a way of recognizing the female as a mate rather than a meal.

Clearly, smelling and tasting are imperative for successful mating in lobster.