The largest population of horseshoe crabs in the world lives in the United States, in the Delaware Bay. Although the horseshoe crab's sword-like tail may look dangerous, this animal is harmless. In fact, the health of the horseshoe crab is critical to the health of both the coastal ecosystem and humans. Horseshoe crabs are important because their eggs provide food for migrating shorebirds, which stop along the Delaware Bay shores each spring to rest and feed on the protein-rich eggs before resuming their flight north to breeding and nesting grounds.
Some birds double and even triple their weight on horseshoe crab eggs.
The horseshoe crab is also invaluable to human health. If you or someone you love has ever been hospitalized, it's likely that the horseshoe crab played a role in your recovery. A clotting factor in the crab's blood, which can be removed without harming the crab, is used to detect bacteria in human blood, in intravenous drugs, and even in prosthetics such as heart valves prior to implantation. Human eye research also has been advanced by studies of the horseshoe crab' s large compound eyes and optical nerve. This research has resulted in several Nobel prizes.