Beachgoers up and down the East Coast have been coming across horseshoe crabs. And that's because it's time for the marine arthropods to mate.

Last weekend, the National Parks Service on Fire Island posted a photo on Instagram, noting, "Have you seen horseshoe crabs on Fire Island? Keep an eye out: Horseshoe crabs come ashore around the new and full moons of May and June to mate and lay eggs."

"During the spawn, the larger female crabs, with one or more male crabs in tow, dig into the sand at high tide and lay 80,000 to 100,000 eggs in a clutch, where the male will fertilize them," according to the Press of Atlantic City. And this is what that looks like:

The NY State Department of Environmental Conservation has closed areas to hand harvests of horseshoe crabs, but there is no total moratorium on harvesting. Horseshoe crabs are sought after because of their blood's clotting properties.

It's also considered to be an aphrodisiac in some cultures; in April, a woman was issued a summons for harvesting the crabs in Plumb Beach for her business.

Last year, Gothamist's Emma Whitford went to Calvert Vaux Park to watch the spawning and wrote:

The biggest threat to New York City horseshoe crabs is the proliferation of bulkheads—especially since Hurricane Sandy. Before the Parks department restored Calvert Vaux in 2012, horseshoe crabs weren't able to spawn there. "They would just hit the wall and swim around and that was it," [NYC Parks Department projects manager Ellen] Hartig recalled.

City-wide, Calvert Vaux is the only sandy slip that's been restored specifically as a spawning ground for horseshoe crabs. "The things people do to protect their property are affecting the intertidal zone," [Cornell Cooperative Extension marine educator Matt] Sclafani said. "If the crabs can't lay on the beach, they can't survive."

But horseshoe crabs are notoriously resilient. Coney Island Creek is connected to a sewer overflow pipe that releases road water and, when it rains, sewage. The night we visited, one horseshoe crab swam along with a piece of toilet paper trailing from his shell.

A post shared by SJP (@sarahjessicaparker) on

Have you been noticing more horseshoe crabs than usual at your local beach?