One of nature’s most extraordinary survivors. Found along the eastern shores of North and Central America—from Maine down through the Gulf of Mexico and as far as the Yucatán Peninsula—it is the only horseshoe crab species native to the Americas. Often called a “living fossil,” this animal has existed in nearly the same form for over 200 million years, long before mammals, birds, and even flowering plants evolved. Its hard, helmet-like shell and long tail spine make it look armored and prehistoric, and in many ways it is. Unlike true crabs, though, it is more closely related to spiders and scorpions, making it a fascinating example of how appearances can be deceiving in evolution.

What sets the Atlantic horseshoe crab apart from its Asian relatives is its size, range, and life cycle. It is generally the largest of the living horseshoe crabs. Their anatomy is remarkable: a rounded carapace, five pairs of walking legs, and a long, rigid tail, or telson, that serves as a balancing tool rather than a weapon. Their eyes are another unique feature. In addition to compound eyes on the sides of their shell, they have five smaller eyes on top that are sensitive to light, helping them navigate both shallow tidal waters and moonlit beaches during breeding season. Perhaps the most dramatic behavior of the Atlantic horseshoe crab is its spawning ritual. Thousands crawl ashore in massive gatherings each spring, especially during full and new moons. Males often attach themselves to females, hitching a ride to the nesting site while she buries tens of thousands of eggs in the sand.

The Atlantic horseshoe crab is a relic of ancient seas and a cornerstone of modern ecosystems and medicine. Its eggs are a vital food source for migratory shorebirds like the red knot, which times its long journey from South America to the Arctic to coincide with the spawning season. Without their energy-rich eggs, these birds would struggle to survive their migration.

Distribution

Country

Population est.

Status

Year

Comments

Gulf of Mexico

2016

Mexico

2016

United States

2016