The Delaware Bay hosts the world’s largest concentration of spawning horseshoe crabs. People come from all over the world to view the spawning crabs and the associated migratory shorebirds. Horseshoe crabs can be viewed on several Delaware Bay beaches and from DNREC’s DuPont Nature Center.

When Spawning Occurs

The bulk of annual spawning typically occurs in May and June and is usually highest around the new and full moons. Spawning coincides with the daily high tides. Often, the highest numbers are present during the nighttime high tide. Choosing to view the crabs at night allows the shorebirds to feed undisturbed during the day.

It is important to remember that horseshoe crabs will delay spawning in rough surf, to avoid being stranded.

Male and Female Horseshoe Crabs

Males can be distinguished from females by their typically smaller size and the presence of a clasper (a boxing glove-like structure) on their first pair of walking legs.

When engaged in spawning, the female may bury herself to an extent that only the males are apparent.

Males often greatly outnumber females on the beaches.

When You Visit

A few things to keep in mind when going to view the crabs (particularly at night).

• Have clothes available for cool weather. It can be clear, calm and warm less than a mile inland, but unusually cool, breezy or foggy on the beach. It’s always a good idea to bring along a dry change of clothes.
• Boots or old sturdy sneakers are a good choice in footwear.
• Biting flies can be troublesome, particularly on warm, calm nights.
• Take some water with you. It is often very hot on the bay beaches.
• Note where you access the beach.
• At night, keep your flashlights pointed down and voices low to avoid disturbing beach residents that otherwise welcome your interest in viewing this amazing spectacle.
• Consider doubling up! Use the daytime portion of your visit to view migratory shorebirds and focus on the crabs at night.
• Keep in mind that the shorebirds don’t arrive until May and are usually gone by the first week in June.
• Look for the crab’s little green eggs (just a little smaller than a BB) on the beach’s surface. Later in the season, developing eggs get clear and the tiny larva can been seen swimming inside.
• Leave only footprints in the sand…take your trash with you!

For more information on Delaware’s horseshoe crabs, contact DNREC Fisheries Biologist Jordan Zimmerman at 302-735-2960 or Jordan.zimmerman@delaware.gov.

Related Topics:  dfw, fish and wildlife, fisheries, fishing, horseshoe crabs, outdoors, outdoors and recreation, recreation, research