Hermit Crabs Are Dying by the Millions After Swapping Their Shells for Plastic

Hermit crabs look pretty vulnerable outside of their shells - and plastics are no replacement. Arnstein Rønning/Wikimedia Commons [CC license 3.0]

If turtles with straws in their nostrils or seabirds with stomachs full of garbage weren't enough to rouse your concern about plastic pollution, perhaps this will: hermit crabs are now the latest victims of the endless barrage of plastic waste washing upon our shores, reports The Washington Post.

Hermit crabs, of course, are those adorable little beach bugs that occasionally peek out from underneath sea shells. Part of what makes them so cute is their vulnerability; hermit crabs are not born with shells of their own. Instead, they take residence in the shells of other critters — often, sea snails — after those shells have been vacated by their original inhabitants. As hermit crabs mature, they outgrow their shells and must swap them out for newer, larger ones.

But as plastic trash accumulates in our oceans and increasingly collects along our shorelines, we're now seeing a disturbing new trend in hermit crab shell-swapping behavior: they're trading in their shells for plastics, and with dire consequences.

This was just one of the findings of a shocking new study about plastic waste in the Cocos (Keeling) Islands, a remote chain of islands in the Indian Ocean. Despite their isolated location, researchers found that these islands were "literally drowning in plastic": 414 million pieces of the synthetic stuff, to be exact.

As they scoured through the heaps of trash, the team began noticing another morbid tendency. Scoops of dead hermit crabs kept pouring out of overturned plastic containers.

It was easy to figure out what had happened. Hermit crabs are instinctually drawn into small crevices and holes during their near-constant search for new homes. Unable to distinguish between artificial containers and shells, they crawled inside the plastic tombs only to become trapped, unable to climb back out of the slippery, unnatural environment.

To make matters worse, hermit crabs emit a chemical signal when they die to alert others that their shell has become vacant. So the plastic containers only become more alluring as they entomb growing numbers of crabs.

"It's not quite a domino effect. It’s almost like an avalanche," explained Alex Bond, a curator of London’s Natural History Museum, which assisted in the study. "Hermit after hermit going into these bottles thinking they'll get their next home, when in reality, it's their last home."

In total, researchers estimate that 570,000 crabs were killed in this fashion in Cocos alone, which is composed of 27 islands. These are very small islands, however. Imagine how this might be harming hermit crabs around the world.

Right now it's too early to say exactly how steeply hermit crab populations might be declining, but if the relatively small sample size of this study is a clue, the numbers will be significant. "This is a perfect opportunity for those who were thinking about getting involved” in beach cleanups, said Jennifer Lavers, who headed the research team. "It's not just removing plastic from the beach because it's unsightly, but it's potentially doing a lot for hermit crab populations."