Horseshoe crabs mate in spring and summer on sandy, protected beaches. (Amy Roe/Flickr)
The horseshoe crab is a primitive-looking arthropod with a hard, brownish-green exoskeleton and a spike-like tail. It visits the Chesapeake Bay’s sandy beaches each spring and summer to spawn.
Appearance:
Hard, rounded, brownish-green exoskeleton
Spike-like tail
Widely spaced eyes that look like bumps on the top of the shell
Five pairs of jointed legs
Gills have folds of membranes that look like leaves of a book
Juveniles are sand-colored
Grows to 2 feet long
Habitat:
Juveniles are found in shallow, protected waters with a sandy bottom
Adults live in deeper waters
Range:
Found year-round in the middle and lower Chesapeake Bay, as far north as the Chester River
Most visible in spring and summer, when it spawns on sandy beaches
Feeding:
Eats mostly worms and mollusks such as razor clams and soft shell 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
Spends most of its time rooting through bottom sediments looking for food
Predators:
Several types of shorebirds eat horseshoe crab eggs
Various fish, invertebrates and sea turtles feed on eggs and larvae
Humans catch adult horseshoe crabs to use as bait and for medical research
Reproduction and Life Cycle:
Spawning takes place in spring and summer (peaking in May-June), usually during evening high tides when the moon is full or new
Large numbers of adults crawl up onto sandy, protected beaches to mate and lay eggs
Females lay clusters of about 4,000 greenish eggs in the sand around the high-tide mark. They return to the beach to lay more eggs during high tides throughout the season.
Eggs take about one month to develop and hatch
Young swim to shallow, sandy, protected nursery areas, where they remain for up to two years
Other Facts:
Horseshoe crabs are not true crabs. They are more closely related to terrestrial spiders than blue crabs.
Horseshoe crabs have existed for more than 300 million years
Although their spikes and spines may look dangerous, horseshoe crabs are harmless
Just like other arthropods, horseshoe crabs must molt to grow. They leave their old shells behind and grow a new, larger shell.
Horseshoe crabs swim upside down
Can survive out of the water for an extended period of time if its gills are kept moist
