Nature

The link between the horseshoe crab, which has remained the same for some 350 million years, and the red-knot shorebird, is explored. The horseshoe crab's spawning grounds, the Delaware Bay, are an important feeding ground for the red knots on their way from Tierra del Fuego to the Arctic. Included: how biologists connected a drop in the red-knot population to a similar decrease in the crabs. Also: how horseshoe-crab blood is used to test human medicines.