Lobster claws grow and change throughout life.Claws of the earliest juvenile lobsters make up only about 5% of total body weight,while the largest adult males can carry almost 50%of their weight in the claws.

Male lobsters develop proportionately larger claws than females of the same weight once they reach sexual maturity. Sexually mature males boast an enormous crusher claw that is highly attractive to female lobsters.

Lobster claws become asymmetrical, meaning uneven,during development. Handedness is based on the side of the dominant,bulkier crusher claw.

The crusher claw has large,rounded, molar-like teeth on the outside. Inside, the closer muscle of the crusher is comprised of 100%slow-twitch muscle fiber.Slow-twitch muscles are noted for strength and endurance and are characterized by their ability to sustain long, strong contractions.

The fast lobster claw has a variety of names,including cutter,pincher,and seizer.This claw has a serrated edge with great tufts of sensory hairs lining the sharp, pointed teeth.On the inside,the closer muscle of the seizer is made up of fast-twitch muscle fibers.Fast-twitch muscle is characterized by rapidity,but is less able to sustain contractions for long periods of time.

By the time a young lobster begins benthic life by settling to the bottom, it has two claws.However,the claws have not yet differentiated into a crusher and seizer.In the beginning,each claw has both fast-and slow-twitch muscle and there is an equal probability of the lobster becoming right or left handed.Claw type is not preordained genetically. Instead,handedness is shaped during the first two stages of benthic life depending on which claw is used the most by the juvenile lobster.

If a lobster is deprived of sediments in the first juvenile stages, claw differentiation fails to occur and the lobster develops two seizers.By depriving juvenile lobsters of substrate and prodding either one or the other claw on a daily basis, experimental biologists can cause the manipulated claw to become dominant.

Although scientists have been unable to encourage lobsters to develop two crusher claws,double crusher lobsters are sometimes seen in nature. While both claws resemble crushers on the outside,they differ in composition of the muscle tissue.The true crusher has 100% slow-twitch fibers in the closer muscle,while the other claw has 40%fast fibers and closes more rapidly.

Once the claws have developed as crusher and seizer,the lobster remains right-or left-handed throughout life. A missing claw regenerates to replace the type of claw that was lost.