Horseshoe Crab Migration Arriving on Maryland Shores

Annual Event Spawns New Generation of ‘Living Fossils’

Maryland’s shores welcome back the annual return of the horseshoe crab – Limulus polyphemus — in one of the world’s oldest and largest wildlife migrations. 

For an estimated 350 million years, these prehistoric creatures have migrated into Maryland’s coastal bays from their winter habitats to spawn along the coastline and subtidal habitats. Although called “crabs” they are in fact arthropods.

The height of horseshoe crabs spawning revolves around late spring and early summer high tides, culminating on or around each full and new moon in June.  On average, one spawning female horseshoe crab will deposit 20,000 eggs into the sand.  

Biologists from the Maryland Department of Natural Resources monitor the returning horseshoe crab population for ecological and scientific research purposes.  The department encourages the public to report any spawning activity and sightings of horseshoe crabs to the Horseshoe Crab Volunteer Angler Survey. 

The horseshoe crab’s blue copper-based blood is critical for biomedical research — the animals are collected by specially permitted fishing operations, have blood drawn in a biomedical facility, and then are released back into the water. 

Also, horseshoe crab eggs are a natural part of the diet for migratory shorebirds preparing to return to their summer nesting grounds in northern Canada. 

Despite a horseshoe crab’s armor and menacing tail, they are gentle creatures that do not bite or sting, and can only survive outside of water for a short amount of time.