Majoid crabs are also known as decorator crabs due to their practice of meticulously covering themselves in materials found in their environment.
Scientists have suggested that this behaviour was a means of camouflage, but were unsure which environmental factors were the cause of it.
“The Indo-Pacific decorator crab Camposcia retusa is a perfect study example,” says Danielle Dixson, a marine scientist and assistant professor at the University of Delaware. “It has Velcro-like substances on its shell and hooks on its appendages that enable it to secure items on its exterior.”
The study crabs were placed in individual containers, and while all were provided with craft pom-poms, only half had access to a shelter.
The scientists photographed the crabs over a 24-hour period then analysed the results. All of the crabs were fully decorated, with most having completed their task within the first six hours. Such speed suggests that the behaviour is an important predator adaptation.
While some other species decorate their bodies first, the scientists noted that the study species placed items on their appendages first when the shelter habitat was present.
Other crabs usually protect their vital organs first, but Dixson points out that the crabs’ legs were still visible when hiding.
The team now want to discover if the crabs choose items of a particular colour, or if their selection is based on smell, known as chemical camouflage.