Picking their way along the squishy banks of the Bagaduce River, a group of about 30 people searched the shallow, warm waters for a prehistoric creature. The horseshoe crab, with a round, spiny exoskeleton shaped like a horseshoe, has a clear lineage stretching back more than 400 million years, before the dinosaurs.
During high tide on June 20, the day of the summer solstice and the full moon, the Blue Hill Heritage Trust guided local residents to find these ancient creatures.
“This is a huge turnout,” said BHHT outreach and development coordinator Chrissy Beardsley Allen during the event. “People are jazzed about horseshoe crabs.”
The walk started at the trailhead of the Maude E. Eugene Snow Natural Area in Brooksville, where people of all ages followed BHHT board member and local naturalist Sarah O’Malley into the forest. After about 10 minutes of walking along an easy hiking trail, the group clambered down a slope to emerge onto the muddy, grassy banks of the Bagaduce River.
Then they began the search.
Horseshoe crabs spend the majority of their time feeding in the deep sea, far from land, but each spring, they swim ashore to spawn, typically at high tide and during the new and full moons. Farther south, on Chesapeake Bay, horseshoe crabs swarm sandy beaches by the thousands to spawn in late May and early June, but in Maine, the northern edge of their range, horseshoe crabs are less common.
“They come up the Bagaduce River looking for nice warm water,” O’Malley said. “They look for soft sand, mud, and prefer salinity that’s 20 parts per thousand … that makes this a good spot for them.”
In Maine, horseshoe crabs are also found breeding in places such as Damariscotta River Estuary and in Taunton Bay, which is the farthest location north that they’ve been documented breeding.
On June 20, the group spotted two horseshoe crabs near the muddy banks of the Bagaduce River. Linked together in the natural embrace of a mated pair, the two creatures were swimming slowly in the shallows.
During breeding season, males arrive at the shore first and await the females, according to the National Wildlife Federation’s online Wildlife Library. When the females arrive, they release pheromones that attract the males. Once a male horseshoe crab finds a female, he latches onto her with his front claws and together, they swim to shore. Near the high tide mark, the female digs a small nest to deposit her eggs, which the male fertilizes. The eggs hatch in about two weeks, and the offspring appear as miniature versions of the adult, though missing their tails.
Wading into the water, O’Malley carefully picked up the female horseshoe crab by grasping the lip of its bowl-shaped body on both sides. The male, robbed of his mate, slowly swam to a nearby boulder and lingered there, as if waiting.
The group of walk attendees congregated at the edge of the water.
“These are the eyes,” O’Malley said, pointing to two bumps atop the creature’s hard exoskeleton. “And then there are actually some other eyes lower down as well.”
As marine arthropods, horseshoe crabs are closely related to arachnids. Their body is divided into three sections, they have 10 walking legs and nine eyes scattered throughout their body, including two large eyes at the top of their head that are used to find mates. They also have light receptors near their tails to help them determine movement and changes in moonlight.
As O’Malley held the creature, its legs, each tipped with a harmless pincher, moved along her forearm.
“Is it tickling your arm?” a woman called out from the group.
“Um, yeah,” O’Malley said to a chorus of laughter. “It feels a little weird. I’m not gonna lie.”
“Let me give her a little breath here,” she said, bending down to place the animal in the water. “And then, if you guys would like to get a closer look, you’ll be welcome to.”
After a minute of letting the horseshoe crab breath through its gills, O’Malley handed the animal to 5-year-old Lena Fisichelli of Winter Harbor. She had been at the front of the group the whole time, listening to O’Malley talk about the creature. With its round body cradled in her small hands, Lena stared at its many moving legs for a few moments, then handed the animal back to the naturalist.
Though its spiny body and long, sharp tail gives the horseshoe crab the appearance of being dangerous, it’s a harmless creature. The tail’s main purpose is to flip the animal over if it gets caught on its back.
As people took turns inspecting the ancient animal up close, someone from the group found a male horseshoe crab. O’Malley pointed out the differences between the two — the male’s smaller size and his larger front claws, which he uses to latch onto the female.
At the conclusion of the talk, the two were released together into the warm waters of the Bagaduce River to carry on with the natural ritual that has kept their species roaming the ocean for millions of years.
To learn more about Blue Hill Heritage Trust and their public nature programs, visit bluehillheritagetrust.org, call 374-5118, or visit the land trust’s office in the William Carleton House at 258 Mountain Road. The office is open year-round, 8:30 a.m. to 5 p.m. Monday-Friday, but due to a small staff, it may sometimes be unexpectedly closed.