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, with the preponderance of plastic waste in nature offering other options to the usual discarded snail shell.
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 as a shell, covering 10 of the 16 known terrestrial species.
It is thought that the crabs are using scraps of rubbish instead of shells for a variety of reasons, including the sheer amount of litter that there is, which makes it a readily available resource.
Dimethyl sulphide
Novel 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 therefore easier to carry, they add. A third possible reason for plastic ornaments being worn by the crustaceans 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.
DMS from plastic, therefore, gives the same smell signal as a natural shell.
Another reason for plastic shell use is that it could be strong and camouflaged, helping the animals avoid predation.
The scientists do not yet know whether the switch to anthropogenic shells is harmful to the crabs, and call for more research to be conducted to analyse impacts on fitness.
Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
