Few animals, it would seem, have done more to help humans than the horseshoe crab.

“They are super important to us medically,” said Mark Bullinger of this sea creature.

A naturalist for the Weekapaug Inn, Bullinger recently led a group of us on a field trip into the shallow waters of a salt marsh to observe mating horseshoe crabs and told us their blood has a clotting agent in it that detects toxins and bacteria harmful to humans.

Bullinger said horseshoe crab blood is used to test vaccines and intravenous solutions for contaminants.

If the solution has any bacteria, “It coagulates and turns to jelly,” Bullinger said.

Startled by this news, I did some digging online and learned horseshoe crab blood is also used to test medical equipment that has come in contact with the human body; spinal fluid for bacterial contamination, like spinal meningitis; urinary tract infections; food spoilage; and quality of air and water. How amazing is that!

In 1971, scientists discovered horseshoe crab blood has a compound in it called, Limulus Amebocyte Lysate, or LAL, “which immediately binds and clots around fungi, viruses and bacterial endotoxins,” according to pbs.org.

Since then, harvesting horseshoe crab blood has become big business. Pharma companies, for example, extract the copper-rich, blue-colored blood from about 250,000 horseshoe crabs (without killing them) and sells the valuable fluid to medical facilities for $50 million annually.

Bullinger said Pharma companies are careful to harvest less than 30 percent of the horseshoe crab’s blood. Then they tag the crab, place it in a holding pen for 1-2 weeks to allow the animal to recuperate, before releasing them back into the wild.

Wading in ankle-deep water, Bullinger occasionally bent down and picked up a horseshoe crab (females are almost twice the size of males) to show us their anatomy. He said the spike-like tail of a horseshoe crab, called a telsen, is not a weapon, but a “tool,” used to right the animal when they’ve been flipped on their backs by waves or ocean currents.

From roughly spring to mid-summer, thousands of male and female horseshoe crabs crawl out of the deep to spawn and lay their eggs along our shorelines, Bullinger said.

Female horseshoe crabs can lay up to 20,000 eggs each, which provide a valuable food source to many migratory shorebirds.

Bullinger said horseshoe crabs are not actually crabs, but arthropods, related to ticks, spiders and scorpions. “That said, horseshoe crabs are completely harmless,” Bullinger said, adding, “They are very gentle creatures.”

He also said fossils of horseshoe crabs have been carbon dated to the Ordovician period, some 450 million years ago.

“They are literally living dinosaurs,” Bullinger explained.

Finally, our talented guide said horseshoe crabs can live up to 40 years — and have helped save the lives of many humans.

Bill Hobbs is a life-long wildlife enthusiast and lives in Stonington. He can be reached at whobbs246@gmail.com.