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For each COVID-19 vaccine shot in the arm, we have the horseshoe crab—and the collaboration between a Johns Hopkins immunologist and hematologist—to thank.

Fear at first sight: That was Jack Levin's reaction upon meeting the creature that put him on the path to lasting scientific achievement. The year was 1963, two years before Levin would begin a 17-year stint on the faculty of the Johns Hopkins School of Medicine. He was a hematology fellow at this point, shipped up to Cape Cod for a summer research project at the Marine Biological Laboratory.

Levin met his new boss, , and soon followed the then chair of Pathobiology at the Johns Hopkins School of Hygiene and Public Health into a primitive-looking laboratory containing a rudimentary "sea table" and a dingy aquarium tank. When the prehistoric-looking marine arthropods inside that tank moved, seawater splashed onto the floor.

"Pick one out," Bang said, pointing to the creatures. Levin knew nothing of Limulus polyphemus, or horseshoe crabs as they're commonly known. On first glance, the creature looks to be 10 claws set under a military helmet and backed by a long, malevolent-looking tail. They can grow to be 19 inches long.

"I was scared to death," he says. 

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