Their diet mainly consists of clams, worms, and other invertebrates. Horseshoe Crabs reach sexual maturity in eight to 10 years after about 17 molts and may live as long as 18 years. The appearance of the shell is a general indicator of the age of this animal . As the horseshoe crab ages, the shell is exposed to a sand-abrasive environment, the larvae of epibionts, and diseases. They are the most active at this age making them more difficult to catch.
Females have large black areas on the middle and back portion of the abdomen caused by mating.
These adults are usually sluggish. Horseshoe crabs reproduce in the spring during lunar high tides. The female digs a shallow nest in the beach where she deposits approximately 2000 to 30,000 large eggs. Meanwhile the smaller male is clasped onto the female's carapace and fertilizes the eggs as she is laying them. The eggs hatch following the next lunar high tide and the crab larvae swim into the surf.