The Delaware Bay is home to the world's largest population of spawning horseshoe crabs. Photo by Michael Darcy

Annual spring horseshoe crab migration celebrated at ‘Sunset on the Bay’

By Isabella Darcy | June 23, 2025

Horseshoe crabs travel onto mid-Atlantic coasts every spring to spawn during what is believed to be the world’s oldest and largest wildlife migration, dating back an estimated 450 million years.

The Delaware Bay is home to the world’s largest population of spawning horseshoe crabs.

The spring horseshoe crab migration happens between March and July, peaking from mid-May until mid-June. On June 14, New Jerseyans gathered along the Delaware bay shore for the third annual Sunset on the Bay event hosted by the American Littoral Society, an organization that aims to empower people to care for coasts.

Sunset on the Bay celebrated horseshoe crabs and the local community, and raised awareness about the vast migration. At the event, members of the American Littoral Society answered questions that attendees had about horseshoe crabs. Members also served food and cast a net into the bay to temporarily catch horseshoe crabs and other wildlife, so the community could learn about what lives in their bay.

Many of those who attended Sunset on the Bay were self-proclaimed horseshoe crab fans because of the many useful roles the marine arthropods assume.

The horseshoe crab spring migration aligns with the migration of hundreds of thousands of red knots, birds that are making their way from South America to Arctic breeding grounds. Those birds stop at Delaware Bay beaches for approximately two weeks to rest and feed on horseshoe crab eggs and larvae, which is imperative to their survival.

Horseshoe crabs also play a significant role in human healthcare. Their blood contains a protein that can act as a clotting agent, and is used by pharmaceutical and medical device manufacturers to test products for the presence of bacterial substances that can cause fevers and even be fatal to humans.

Members of the American Littoral Society told Delaware Currents that they enjoy hosting Sunset on the Bay, and hope to continue holding the event in years to come.

Attendees at the June 14 Sunset on the Bay event hosted by the American Littoral Society. Photo by Michael Darcy

Isabella Darcy

Isabella Darcy is a student at The College of New Jersey where she is studying journalism and professional writing. She serves as a managing editor of TCNJ's student newspaper, and has worked with numerous local news outlets in the past. She enjoys learning new things and bringing stories to light.

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