Horseshoe crab blood is key to making a COVID-19 vaccine—but the ecosystem may suffer.Conservationists worry the animals, which are vital food sources for many species along the U.S. East Coast, will decline in number. Each spring, guided by the full moon, hundreds of thousands of horseshoe crabs clamber onto beaches across the U.S. mid-Atlantic to lay their eggs. For hungry birds, it’s a cornucop
![Horseshoe crab blood is key to making a COVID-19 vaccine—but the ecosystem may suffer.](https://cdn-ak-scissors.b.st-hatena.com/image/square/871751213c1cad6e9bc24596bc59253facd513e9/height=288;version=1;width=512/https%3A%2F%2Fi.natgeofe.com%2Fn%2Fa44c1d56-6382-4371-9dde-83f790d5699c%2F01-horsehoe-crab-harvesting-nationalgeographic_1092243_16x9.jpg%3Fw%3D1200)