Hermit Crabs are Making Homes in Plastic Instead of Shells and It’s Killing Them

At least half a million hermit crabs have died trapped in plastic “shells” too slippery to climb out of, study finds

Australian researchers surveyed the Cocos Islands and found hundreds of thousands of hermit crabs trapped or dead in plastic containers they mistook for shells.

The islands – once thought of as a tropical paradise – are “literally drowning in plastic,” the researchers say.

Hermit crabs mistake plastic cups, buckets, bottles and other debris for shells, climb in, and then can never climb back out because the plastic surfaces are too slippery to get traction.

Whether they are trying to get out because the home is too big, or because they’ve outgrown it, they are stuck, the study‘s authors explain.

“When we were surveying debris on the islands, I was struck by how many open plastic containers contained hermit crabs, both dead and alive,” said Jennifer Lavers, lead study author and researcher at the University of Tasmania’s Institute for Marine and Antarctic Studies.

She and her team counted an average of one or two trapped crabs per square meter, estimating 508,000 had been killed on the Cocos Islands, and 61,000 on Henderson Island.

Each plastic “shell” is used by untold numbers of crabs, as they emit a chemical signal to other crabs when they die, alerting them that there is a shell now available and attracting them to it, the researchers explain.

“Hermit crabs play a crucial role in the health of tropical environments by aerating and fertilizing soil, and dispersing seeds and removing detritus, as well being a key part of the marine ecosystem,” Lavers said.

“Their population degradation is more than just a risk to the natural environment. They are also an important part of marine ecosystems that humans rely on for fishing, recreation and tourism, so ultimately the impacts may also be economic.