Mashomack Musings — Living Fossils on Shelter Island

Did you know we have a pre-historic species on Shelter Island? Horseshoe crabs, often called “living fossils,” pre-date the dinosaurs by 200 million years.

Horseshoe crabs spend summers in shallow water, plowing through sand and feeding on small clams, crustaceans, worms and algae. Their harmless spike-like tail is not a stinger, and simply serves as a rudder.

On sandy beaches in May or June they lay greenish-tan eggs, which are an important food source to coastal birds. Interestingly, they are not officially crabs, but are more closely related to spiders, scorpions and ticks.

Despite their hard exoskeleton and persistence as a species, horseshoe crabs are sensitive to their surroundings. Their copper-based, blue blood is significant to the medical field because the blood will clot quickly in the presence of bacterial toxins. This allows it to be used to test for the sterility of medical equipment, intravenous drugs and vaccines.

Horseshoe crabs can be found along the East Coast. But their populations have been declining. Although the species has been on Earth for over 400 million years, horseshoe crabs are not immune to the growing pressures of humans. They’ve been continually harvested for bait and biomedical research and are losing habitat as a result of human development and sea level rise due to climate change.

If you happen to see a horseshoe crab overturned on the beach, pick it up on both sides of its shell and move it into the water.

Do your part in protecting this ancient species.