By Victoria Gill
Science and nature reporter, BBC News
Baby fiddler crabs take up refuge in seashells
Baby fiddler crabs "move in" to empty snail shells for shelter, scientists have found.
Researchers made this discovery whilst studying salt marsh ecosystems on Tybee Island in Georgia, US.
The finding shows how "resourceful" these primitive crustaceans are, they say, as unlike hermit crabs, fiddlers do not carry seashells on their backs as a permanent home.
It also reveals how crabs can benefit when snails are eaten by predators.
Professor Sophie George from Georgia Southern University in Statesboro, who led the study, explained that fiddler crabs are important in the establishment and maintenance of the salt marsh ecosystem.
In the Journal of Experimental Marine Biology and Ecology, her team explained that the crabs were a source of food for many animals.
"They are eaten by resident and migratory birds, by [other] crabs and by shrimp and fishes," wrote the researchers.
"Small mammals and reptiles feed on fiddler crabs as they move across the salt."
The tiny baby crabs - with a soft shell less than 3mm wide - are particularly vulnerable.
"Settlement of the first fiddler crab stage during high tide exposes them to a variety of habitats but also to predators," said Professor George.
On top of this, the juvenile crabs are too small to dig their own burrows.
Previous studies had found that some animals used shells for shelter.
So to find out if the baby fiddler crabs might also hide in the empty snail shells, the researchers visited the island 20 times to collect the shells.
Out of every 100 empty shells, they found that 79 were occupied by the tiny crabs.
Professor George said: "An abundance of Littoraria irrorata [snail] shells [provide] a welcome refuge for juvenile fiddler crabs."