Hermit crabs snap up bright litter in hope of finding a mate

HERMIT crabs are using litter as makeshift shells in an apparent attempt to find a mate, scientists have discovered.

Plastic caps are the most popular form of rubbish adopted by terrestrial hermit crabs, data show.

Two thirds of the 16 known terrestrial hermit crab species were found to have used litter as a shell by scientists from Poznań University in Poland.

Photographs posted online by members of the public were analysed and a total of 386 crabs were seen using waste rather than natural snail shells, covering 10 of the 16 known terrestrial species. The increase in the amount of litter in the sea was believed to be one of the reasons for the change.

Shells made of plastic are also more colourful than some natural options, the scientists say, which may be useful in attracting a mate. “Artificial shells may be attractive for females, as novelty per se is a premium in the evolution of sexual display and sexual selection,” the authors write in their study, published in Science of the Total Environment.

Crabs may be choosing plastic over snail shells because they are lighter and easier to carry, they add. A third possible reason is that the creatures are drawn to a chemical that the plastic emits called dimethyl sulphide (DMS).

This chemical is also produced by the decomposing bodies of dead crabs, and hermit crabs that detect it are drawn to the odour as they know it will present an opportunity to steal their shell.

The scientists do not yet know whether plastic shells are harmful to the crabs, and call for more research to analyse their effect on crab fitness.

Because of the rising amount of litter in the ocean, hermit crabs are using brightly coloured plastic waste as their shells – which increases their odds of finding a mate