Mass Gatherings
When hundreds of thousands of horseshoe crabs cover Delaware Bay beaches
Every spring, Delaware Bay beaches become spawning grounds for enormous numbers of horseshoe crabs, creating one of the East Coast's strangest seasonal wildlife spectacles.
Video: National Geographic. Embedded from the original YouTube source.
Delaware Bay can look completely overrun when horseshoe crab spawning peaks. The animals move out of deeper water, crowd into the shallows, and climb onto beaches in numbers large enough to cover the shoreline.
The spectacle is tightly tied to spring conditions and reproduction. Large gatherings are especially visible where protected beaches provide suitable spawning habitat.
What to know
- This is a recurring natural spawning event, not an infestation.
- Peak activity is usually concentrated around spring high tides.
- The eggs are also an important food source for migrating shorebirds such as red knots.
Good questions
What people usually want to know
Why are there so many horseshoe crabs on Delaware Bay beaches?
They gather in large numbers each spring to spawn in shallow water and on suitable beaches.
When is horseshoe crab spawning season in Delaware Bay?
Spawning activity builds in spring and commonly peaks in May, especially around favorable tides.