Scientists Baffled as Hundreds of Dead Horseshoe Crabs Wash Ashore in Japan

Image: AP
Image: AP

Horseshoe crabs are known as “living fossils” and for good reason. The blue-blooded, side-walking arthropods have been around for 200 million years, surviving the last five mass extinctions. But something appears to be wrong as hundreds of dead horseshoe crabs have recently washed ashore in southern Japan, leaving scientists confounded.


One population of horseshoe crabs, or “warrior helmet crabs” as they’re known in Japan, make an annual trek to their spawning grounds around the tidal flats of Kita-Kyushu. Some inevitably die in the process, but the number of dead this year is uncharacteristically high, prompting concern.

As reported in AFP, a local conservation group had been spotting upwards of five to 10 remains every day during the egg-laying period, prompting a more thorough investigation. By the time the conservationists were finished counting they tallied up about 500 dead horseshoe crabs. That’s about eight times higher than normal, and about 20 percent of the local population. It takes a long time for young horseshoe crabs to mature, so this is a major setback for a species already in trouble.

Scientists have been recruited to explain the dramatic death toll, but the cause remains elusive. Going theories include a parasitic infestation or a disease peculiar to horseshoe crabs. Or, it could be because of us; another theory suggests an oxygen shortage due to higher sea water temperature. Though to be fair, horseshoe crabs are known to dwell in warmer waters to the south. But if these deaths are caused by human activity, it be dreadful that we’re causing such trouble for an animal that’s survived for so long.

Helmet crabs are listed as an endangered species in Japan; its population is in sharp decline owing to coastal habitat destruction. But despite the designation, no legal injunctions exist in Japan to get the ball rolling on meaningful conservation efforts. Let’s hope this latest incident sparks both conversation and action. It would be a tragedy to see the demise of one of our planet’s most enduring species.


Senior staff reporter at Gizmodo specializing in astronomy, space exploration, SETI, archaeology, bioethics, animal intelligence, human enhancement, and risks posed by AI and other advanced tech.



I used to see these (the generic variety?) on the beach in my hometown in NJ all the time growing up. Now I never see them. Creepiest looking critters to find when you’re a kid.