Road Trip Adventure- The Crabs of Delaware

The horseshoe crab is possibly the most bizarre critter you will encounter on a sandy Atlantic beach. Resembling a helmet with legs and a tail, they are not actually crabs at all, but are more closely related to spiders. They are nearing the end of their spawning season, and I traveled to Delaware to get some time in the field and see for myself.

Horseshoe crab (left) and traditional  Dungeness crab (right)
side by side for comparison

Horseshoe crab undercarriage

These marine arachnids are an ancient species dating back over 300 million years. I’m sure they’ve been spawning since then, but unlike most sea creatures, they come ashore to lay and fertilize eggs. Mid-May to early June is prime time for spawning. The crabs haul ashore at high tide and they prefer full or new moons. I just happened to arrive a day after full moon, so the event was in full swing when I got there. Check the video raw here. 

Horseshoe crabs spawning at midnight

Males are smaller than females, and will climb on the backs of females to fertilize the eggs as they are released. There are more males than females, so sometimes there will be one or two “satellite males” clinging to the sides in addition to the first male to attach. Females lay a few thousand eggs per shot, and will emerge to spawn several times over the course of the season.

She’s laying that many eggs for good reason: there are tons of migratory and seasonal shorebirds on the coast looking for a quick and easy meal. Eggs and freshly hatched larva really hit the spot. Eggs hatch after two to four weeks. Larva hang out in the shallow water for a few years, while the adults return to the briny deep.

Horseshoe crab returning to sea

Walking the beach the day after watching the midnight spawning, there were a few stragglers. In some cases, all that remained were the crab tracks. The shell plows a path in the sand that ends in a horseshoe shaped depression (or a crab, if it hasn’t made it back to sea yet), which is how the crab got its name. There were also a few dead ones that were stranded after the tide went out. 

Leaving behind a crab track

Seeing a live horseshoe crab for the first time was an interesting experience. I’m not a diver so my only in-person encounters with marine life has been tidepool critters that don’t move, such as a sea anemone. Getting down to the beach and turning on a flashlight and seeing all those crabs together in a writhing, tumbling mass of helmets was incredible. If you ever get the chance to watch, I highly recommend it. Just remember to leave no trace. I picked up about 2 ½ gallons of garbage before leaving.

Nature Minute now has a Youtube channel! I will add videos as I feel like making them. In addition to the video linked above, there are others from my weekend adventure in Delaware. Next week I'll have some stories from the road.