Horseshoe crabs: ancient animals in Casco Bay

Linda Stimpson has lived in Maine for much of her adult life, but it wasn’t until recently that she first spotted this prehistoric creature – with nine eyes and ten legs – scuttling along the shore of Casco Bay.

In her Water Reporter post from July 12, Linda photographed a horseshoe crab on the stretch of beach between Wolfe’s Neck State Park and Googins Island.

“They’re ancient creatures,” said Linda, referring to the fact that these invertebrates have been on earth for over 300 million years (that is even older than dinosaurs). Despite the threatening impression that may come from their spike covered shell and long pointy tail, “they’re really quite docile,” shared Linda.

Adult horseshoe crabs live deep in the ocean, but they search out sandy shores in the spring and summer to spawn. Once on shore, females dig nests in the sand where they deposit their eggs to be fertilized by males. In Casco Bay, horseshoe crabs are known to spawn in Middle Bay and Thomas Point Beach in Brunswick, though Linda’s photo clearly shows that they also make their way further west. Linda also shared that she recently saw a horseshoe crab on the shores of Mackworth Island.

Horseshoe crabs play an important role in coastal food webs, as their eggs are a nutritious food source for fish, turtles, and migratory shore birds. In addition to their ecological importance, horseshoe crabs play a critical role in modern medicine. Their blood is used to test for the presence of bacterial endotoxins in sterile pharmaceuticals, like artificial joints, intravenous drugs, and even COVID-19 vaccines!

Linda, thank you for keeping an eye out for these ancient animals in Casco Bay, and for being a Water Reporter.