Before a horseshoe crab molts it forms a new shell under its old shell.
The new shell has pleats, like a folded umbrella, so it can get bigger
in size. Then, unlike some animals that split their shells along the back,
it splits the front seam of its shell and crawls forward, pulling its soft
body out. It looks like itís crawling out of its own mouth except that
is impossible. The mouth of a horseshoe crab is beneath its shell, buried
between the attachments of the legs. While the crab waits for the outer
layer of the soft skin to get hard, it remains motionless. It may take
a young crab less than an hour to molt. An older crab might take up to
24 hours. While an older crab is molting, it digs down into the sand to
protect itself from predators that could easily bite through the soft shell.
After it molts a crab is about a fourth larger in width and length and
thickness than it was before.
Horseshoe crabs molt throughout their whole lives. It molts for the first time after it leaves the egg sac in six days. Then in the next three or four months, it may molt up to five times, although it is still only about 2.5 cm wide. These are some of the molts of our crabs the first few months.
the first two or three years a horseshoe crab may molt several times. After
that, it usually molts only once a year until it become a mature adult
in nine to eleven years.