Horseshoe Crab

Limulus polyphemus

The horseshoe crab is a primitive-looking arthropod with:

• A hard, brownish-green exoskeleton, or shell.
• A spike-like tail.
• Widely spaced eyes that look like bumps.
• Five pairs of jointed legs.
• Book gills, which have folds of membranes that resemble leaves of a book.

Horseshoe crabs grow to about 2 feet long.

Where does the horseshoe crab live?

Horseshoe crabs can be found year-round in the middle and lower Bay.

• Adult horseshoe crabs usually live in deeper waters, while juveniles stay in shallower waters.
• Horseshoe crabs have been recorded in the Miles, Chester, Choptank and Rappahannock rivers.
• Horseshoe crabs can survive for extended periods of time out of the water if their book gills are kept moist.

What does the horseshoe crab eat?

Horseshoe crabs feed primarily on marine worms and mollusks like razor clams and soft-shelled clams. Because they lack jaws, horseshoe crabs use the spiny bases of their legs to crush and grind their food, then push it into their mouths.

How does the horseshoe crab reproduce?

Horseshoe crab reproduction takes place beginning in May.

• Large numbers of adults move onto sandy Bay beaches to mate and lay eggs. This usually corresponds with full moons and evening high tides.
• Females lay greenish-colored eggs in nests or clusters in the sand, usually at the high tide mark.
• Eggs take about a month to develop and hatch. The next spring high tide breaks the eggs open, releasing sand-colored young that are carried by the tides to the water.

Other facts about the horseshoe crab:

• Horseshoe crabs are not true crabs. They are actually more closely related to terrestrial spiders and scorpions than other crabs.
• The horseshoe crab's external appearance has remained unchanged for the last 360 million years. While their spikes and spines may look dangerous, horseshoe crabs are harmless.
• Just like all other crustaceans, horseshoe crabs must molt to grow. They leave their old shell behind and form a new, larger shell.
• Horseshoe crabs swim upside down. But they spend most of their time rooting through bottom sediments for food.