Hermit crabs using plastic waste for shells, study finds

Hermit crab species are increasingly choosing to use discarded plastic waste as a protective armour for their bodies over shells, a study has found.

Scientists published their research in the journal Science of the Total Environment and found that 10 of 16 terrestrial hermit crab types exhibit this behaviour globally.

They used a research method, known as iEcology (internet Ecology), which analyses photos, published on digital platforms - including Google and Flikr - by wildlife enthusiasts.

Typically, hermit crabs scavenge shells from gastropods (molluscs) for their protection from predators, while previous studies have found that the animals' choice can play an important role when females choose which males to mate with.

But the study identified a growing trend of the crabs now choosing artificial shells, along the majority of tropical coastlines in both hemispheres.

Some 386 photographs were identified in the research as showing a hermit crab wearing an artificial shell, of which the majority (84.5%) were made out of plastic - such as bottle caps.

Metal and glass were the other most common materials identified as artificial shells.

Researchers Marta Szulkin, Zuzanna Jagiello and Lukasz Dylewski hypothesised a number of theories for their findings.

They suggested that a simultaneous rise in global plastic pollution alongside declining mollusc populations were to blame.

Hermit crabs could also choose artificial shells for their protection as a point of preference, although the researchers stressed scientific studies have yet to explore the weight of this theory.

The trend, meanwhile, could have evolutionary implications for hermit crabs, the researchers concluded, and has opened up new questions around how the animals interact with discarded human waste.

Hermit crabs have evolved to scavenge for gastropod shells which, when in short supply, are fought over by competing crabs.

But the introduction of artificial shells could offer a solution to help smaller, weaker crabs survive because of their high quantity and light weight.

The researchers also said they would like to study how the "colour and/or chemical property of the artificial shell may add a further unknown dimension for an ecological or evolutionary trap to arise as artificial shells come in different colours and textures, which do not necessarily correlate with protective attributes".

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