Each spring The Nature Conservancy recruits volunteers to survey two beaches along the Delaware Bay during horseshoe crab mating season (see video of what the survey looks like).

The survey is part of a Delaware Bay-wide horseshoe crab population study, and the data collected each year is used to help set the commercial harvesting quotas for the following years. Fertilized crab eggs are harvested for use as bait in the conch and eel fisheries — and their copper-based blue blood contains a compound important to the human pharmaceutical industry.

The eggs are also the perfect protein-rich food for migrating shorebirds — millions of famished shorebirds arrive as the horseshoe crabs emerge to mate. This may be the birds’ only stop on a 10,000-mile odyssey from South and Central America to the Canadian Arctic, and they depend on the feast of horseshoe crab eggs and insects along the Delaware Bay.

And, since the crabs show the most activity during high tides near the full moon, that’s when the survey teams go out, too — 3 to 4 people walking the beaches with clipboards and survey tools. During the course of the night, they will count (and sex) crabs at 100 points (called transects) going from north to south along the high tide line. One night I joined a few dedicated volunteers on their evening surveys — here’s a diary of how it went:

[5:00 pm] Tornado warnings and thunderstorms are not an auspicious way to start a Saturday evening horseshoe crab survey. But I get my bug spray out, find some shoes that can get wet and head out. I meet my friend and Nature Conservancy member Terri, who offered to help with the survey, and we carpool down to Big Stone Beach in Milford, Delaware.

[7:00 pm] We stop along the way to pick up our surveying materials at the local fire house — they let The Nature Conservancy store the equipment here during May and June each year. Our toolkit for the evening includes: a 20-meter long rope; white plastic pipes (used for building a meter-square measuring device); and a clipboard with our forms all ready to go.

[7:10 pm] Big Stone Beach is located on the Delaware Bay, in the middle of nowhere. We drive down country roads through forests, seeing only occasional homes obscured behind trees. As the trees thin, we see the marsh and finally the beach.

[7:20 pm] Nature Conservancy employees and survey volunteers John, Colin and Peggy  meet us at the beach right before our start time.  After going through introductions, directions, job assignments and bug spray application, we head onto the beach. It looks to be a good night for the crabs, with waves less than a foot high.

[7:22 pm] Colin and Peggy take on rope duty, unraveling the rope so that we walk a distance that is 25 lengths of the rope up the beach to our starting point. Their work is so efficient that we take time to explore before starting with the survey at the 7:52 pm high tide.

This beach does not have the hard smooth surface I am used to…rather it is coarse and lightly-packed, so you sink down a bit with each step you take. The horseshoe crabs can be found swimming throughout the surf. Seagulls and red-winged blackbirds fly above us, and a cool breeze keeps the mosquitoes and flies away.

[7:47 pm] Before getting down to business, we spend some time carefully flipping over the crabs onshore that have been overturned on their backs. Their long tails are not stingers, but a tool they use to help right themselves when turned over. Their little claws make a neat pattern in the sand as they slowly walk along the beach searching for a mate. Looking down the beach, it is remarkable how ungraceful these creatures are in the water — flipping over in the surf, tails popping up through the waves. But while odd to look at, they are pretty harmless.


[7:52 pm] We get to work and begin the survey by walking transects. The 20-meter-length rope is marked off with knots at 7 and 17 meters, marking the location of where we should put the white plastic pipe square down on the sand and water to count crabs (again, watch the video at the top of the post to see how it works).

We walk down the beach at a steady pace and start counting crabs as soon as we had the rope in place. You don’t put it on the ground — the two people with the ropes keep it in their hands and stand still while others go to points 7 and 17 on the rope to do the survey at each spot.

As we get into the swing of things we see plenty of crabs — but none are falling into our surveying square. Zero after zero are recorded as we measure and walk south. “Come to papa!” one of us says, urging the crabs to crawl into our white pipe square — but to no avail.

[8:15 pm] Finally at about the 25th or 26th survey point, we start to find some crabs in our white square! The larger ones buried in the sand are the females, and the smaller crabs clasped on top of them are the males (see photo above). They have a special claw they use to hold onto the female. She lays her eggs beneath her in the sand and the males fertilize them. It seems a slow process.

We watch them roll around in the waves as they swim into the beach. We feel like we are watching one big horseshoe crab party and the only sound that can be heard is the wind and the seagulls as we walk by.

[8:25 pm] In our surveying travels, we see a family who has set-up a stretch of the beach for a picnic and some fishing. I think they thought us a strange lot to be out on a Saturday night counting horseshoe crabs…and not collecting crabs to sell as bait. Colin stops to talk with them as we switch positions and continue down the beach.

[8:35 pm] The number of crabs increases as we walk south. We count the number of males and females at each stop and begin to see a couple females with 1 to 4 males, each struggling to get into position. Sometimes we have to stick a finger down in the sand to see if the female is under the male crab, because the waves can cover the females with sand.

[8:40 pm] On the southern end of our survey, we find small houses built over the beach. No one seems to be home. We walk next to and sometimes under the houses to complete our survey. This is good horseshoe crab counting territory — we have crabs in most of our squares. We’re gaining confidence and have become more relaxed as we continue on. “This is one big crab party now!” somebody says.

[8:50 pm] We reach the 100th station. We complete filling in the form and walk back to the cars. It’s still daylight and the threatening storms never arrived. We complete the entire survey before 9:00 pm! Go team!

Our forms will be sent to Limuli Laboratories in Cape May, New Jersey, where all of the survey sheets collected from teams working on 13 beaches on the Delaware side of the Bay and 13 beaches on the New Jersey side will be analyzed. The data is shared with the Sea Grant Program at the University of Delaware, the state and other government agencies who set the commercial harvesting quotas.

Debbie Heaton is senior associate director of philanthropy for The Nature Conservancy in Delaware.

(Image: Two males and a female horseshoe crab. Source: Terri Tipping.)

If you believe in the work we’re doing, please lend a hand.


  1. Debbie Heaton’s article enlightened my wife and I as we never thought much about horseshoe crabs.Another wonder of nature.

  2. This is so interesting. We have these horseshoe crabs at the Ocean City,NJ beach aLso and everyone inds them fascinating.

  3. What a mysterious and amazing creature! I wish I had known more about them while growing up. We would have appreciated them more.

  4. they are sooo cool

  5. Thank you so very much, and to all others who are helping to protect such a wondrous creature and its (and our) environment.

  6. My daughter and I counted horseshoe crabs last night for DNREC. Wasn’t a really good night for it since the waves were coming in very strong and the crabs weren’t coming in. Even though there weren’t that many to count, it was an amazing sight! We go back Saturday night…hopefully it will be calmer!

  7. Just returned from Primehook beach area in delaware and saw hundreds of hs crabs along the shore. Awesome adventure!

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