Spawning Season Is Nearly Done But Horseshoe Crab Work Isn't

Horseshoe crab tagging participants learn about the anatomy of horseshoe crabs, May 31, 2024

By Trevor Metz, Littoral Society Delaware Seasonal Technician

While the month of June typically sees a decrease in horseshoe crab spawning activity, our work in Delaware hasn’t slowed down at all! I have been from Wilmington to Lewes with a horseshoe crab in tow, helping talking with people and advocating on behalf our state’s official marine animal.

​So far this season, despite a mix of beautiful and inclement weather, we have tagged 200 crabs in support of the Fish and Wildlife Service’s Cooperative Tagging Program. The rain held off during our most recent effort and we were lucky enough to have a beautiful rainbow cap off our evening.

With a full moon later this week, we will host one more tagging event at Slaughter Beach on Wednesday, June 19.

Spawning activity lasts from May through June, and sometimes into July. If you haven’t already, check for a convenient high tide at a local bay beach and witness this ancient migration firsthand!

Horseshoe crab tagging volunteers enjoy a sunset rainbow at Slaughter Beach, June 6, 2024

While most of the migratory shorebirds have moved on from Delaware beaches in their seasonal journeys, the reason for their stop over is still easy to see.

The tiny green horseshoe crab eggs that become valuable forage for migratory birds must be displaced by nesting females. While they will not survive to adulthood, these loose eggs get washed up the beach and can be found along the wrack line.

In years past, large masses of eggs provided a super abundance of nutrients for migratory birds to recover from and prepare for the rest of their migration.

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Crashing waves wash unearthed horseshoe crab eggs into the wrack line, Slaughter Beach, DE, June 6, 2024

The unregulated overharvest of horseshoe crabs 20-plus years ago resulted in a drastic reduction in the number of spawning females, and subsequently the number of eggs available as forage. While less abundant than previously, this food source is still sought after by a litany of birds and marine animals and continues to exemplify why horseshoe crabs are a keystone species in our estuary ecosystem.

During the spawning season, Delaware’s bay beaches are an endpoint of horseshoe crab migration. Sometimes, rather than getting folks out to the shore, it’s easier to recruit a volunteer crab for outreach and education events.

The Littoral Society has made a few new connections in Delaware this month by partnering in such events, which included activities with the Delaware Museum of Nature and Science, Bombay Hook National Wildlife Refuge, and Delaware Sea Grant.

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A cluster of horseshoe crab eggs.

A favorite type of interaction I have is when someone leerily asks: “What is that thing?!” Then we end up chatting long enough to have an understanding and appreciation for how unique, interesting, and important horseshoe crabs are.

Even here in my hometown of Milford, where horseshoe crabs are a familiar sight, there are often misconceptions or misunderstandings that make for great conversation and learning opportunities. Paramount to the Littoral Society’s conservation efforts is sharing knowledge with citizens and empowering them to engage in the conservation issues in and around where they live.

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Original student artwork featured on an advocacy sign.

To recruit some local voices, we worked on a sign contest with elementary students who had recently visited Slaughter Beach, DE.

On their field trip they learned about the importance of horseshoe crabs and how migratory shore birds depend on horseshoe crab eggs to survive their migration. For the contest, we offered a few suggested phrases and recommendations for designs, and wow did these children do a great job!

We ended up featuring five student designs, but the whole class enjoyed some snacks and sweet treats to show our appreciation for their efforts.

Posting these signs on neighboring beaches will help draw attention to the sensitive nature of horseshoe crab spawning sites, the importance of leaving migratory birds undisturbed during their visit, and a general need for humans to be good stewards of nature.  

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My seasonal position with the American Littoral Society is almost finished for 2024, but we still have a few more exciting things coming up this month. We are continuing to make connections here in Delaware, while also working on community relationship, advocacy, and calls to action.

Keep an eye on our upcoming events page, follow us on social media, and hopefully my horseshoe crab volunteers and I will see you soon!​