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Tourism-Related Thai Hermit Crab Boom Causes Crustacean Housing Crisis

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Rachael Funnell

author

Rachael Funnell

Writer & Senior Digital Producer

Rachael is a writer and digital content producer at IFLScience with a Zoology degree from the University of Southampton, UK, and a nose for novelty animal stories.

Writer & Senior Digital Producer

Without a decent shell supply, crabs are forced to opt for trash. FocusMaster/Shutterstock.com

Without a decent shell supply, crabs are forced to opt for trash. FocusMaster/Shutterstock.com

The start of the year saw swathes of positive content (some real, some fake) detailing how nature was “healing” as the anthropause triggered by Covid-19 saw human activity grind to a halt. While the influence of global lockdowns was seen in momentary dips in air pollution and a rise in wildlife sightings, most effects are believed to have been temporary, but for one group of animals in Thailand, the reduction in tourism has caused an unexpected crisis.

Hermit crabs on the islands in the Mu Koh Lanta National Park in southern Thailand have seen their numbers boom by the tens of thousands as travel restrictions have axed the country’s usually thriving tourism industry. Empty beaches free from international tourists appear to have encouraged the crabs to go forth and multiply to the point where there aren’t enough cone-shaped shells for members to move into. Weather, sea currents, and the presence of plankton or predators may have also contributed to the change, but the steep reduction in human traffic will have improved the survival rates of these beach-going species.

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Hermit crabs begin their lives as larval forms on the seafloor. As they grow, they need a hard case to protect the squishier bit of their bodies so they take the cast-offs from creatures like snails or sometimes even living coral. When hermits get too big for their shell, they form a conga line on the shore with other crabs, each queueing up in size order. Once ready, one member will eject themselves from their calcified castle and wiggle their pale tuchus into the available shell of another. The event sees a cascading effect of bare butts seeking neighboring shells, with the desired result being everyone walks away with a new shell that is a better fit than their old one.

The dance requires an ample supply of shells to be effective, but as numbers have boomed in 2020 it seems the hermits can’t get their foot on the property ladder. The hermits are having to get inventive and there have been increased sightings of crabs making do with discarded cans and bits of rubbish, which are far from ideal for a developing hermit. The situation has gotten so bad that the national park authority made a plea on Friday for the public to donate extra shells in the hope that an influx of calcified condos might alleviate the crisis.

A fall in tourism has seen a spike in hermit crabs in Thailand, but there aren't enough shells to go around. LuFeeTheBear/Shutterstock.com

“The reason [we need shells] is because of surging numbers of hermit crabs, I think tens of thousands,” the national park director, Veerasak Srisatjung, told AFP.

The national park authority is inviting people to post cone-shaped shells to its office in Krabi province and has so far received around 200 kilograms (441 pounds) of hermit crab real estate. The donations will be distributed by volunteers during a Thai Father’s Day event on December 5.


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