Horned ghost crabs change camouflage from day to night

Juvenile horned ghost crab in light and dark camouflage The same crab can look very different in the day (top) and at night (bottom)

Horned ghost crabs change their appearance from day to night for camouflage, a study has revealed.

The species Ocypode ceratophthalmus builds burrows on beaches from Japan to East Africa to shelter from predators.

Researchers investigating young crabs' defences found they fine-tune their brightness to mimic their background.

The crabs reflected changes in their environment throughout the day, becoming lighter in the daytime and darker at night.

The findings are published in the Biological Journal of the Linnean Society.

Horned ghost crabs are named for their eyestalks which extend upwards resembling horns. The crabs are mostly active at night and juveniles are slightly translucent.

Dr Martin Stevens, working for the University of Cambridge, undertook the study with colleagues from the National University of Singapore.

"They have a remarkable match to the sand on which they live to provide camouflage against predators like birds and primates," he told BBC Nature.

"They can even match the colours of particular grains of sand found on the beach where they occur."

Scientists first suspected the crabs' unusual day to night colour change after noticing differences in images of them taken at different times.

Camouflage contest

See the fish impersonating an octopus... that mimics a fish!

Watch the dresser crab adopt its disguise

Can you spot a leaf tailed gecko hiding in the jungle?

They tested their theory in the laboratory using crabs collected from beaches in Singapore.

Observing the colour of the crabs over a twenty-four period, they recorded a distinctive change from a dark appearance through the night to the lightest appearance at midday.

When placed in a dark tank, the crabs did not change colour but they did become brighter when placed a on a white versus a black surface.

Dr Stevens explained that, rather than directly reacting to the ambient light, the crabs combined a natural daily rhythm of colour change with reactions to the colour of the surface they occupied.

"This changes their camouflage so that they are very well camouflaged against the yellow sand during the day, and dark at night - we think to blend in with shadows on the beach," he said.

Dr Stevens added that if the crabs simply became darker when in shadow, such as when they enter their burrow, they would then appear very noticeable against the sand when they next ventured out in daylight.

Horned ghost crab, Seychelles Adult horned ghost crabs are unable to change colour to the same degree as the young

This camouflage trick directly contrasts with how other species of crabs alter their appearance to suit their surroundings.

Fiddler crabs from the Uca genus are known to appear darker during the day and lighter at night. Scientists have suggested this may help the crabs to regulate their temperature or protect them from UV radiation in the day.

A further oddity of the ghost crabs, according to Dr Stevens, is the fact that only the juveniles can change their appearance in this way.

"The adults probably don't change colour as much... because the carapace becomes thick and dense with pigment when the crabs get big. But why that should happen I'm not sure," he said.

The biologist intends to investigate other crab species in order to understand more about their ability to change colour for concealment.

Join BBC Nature on Facebook and Twitter @BBCNature.

More on This Story

Related Stories

The BBC is not responsible for the content of external Internet sites

More from nature

  • Cardinal fish and ostracodFish filmed spitting 'fireworks'

    Film crew captures ostracods' spectacular defensive lightshow that makes predatory fish spit them out.

  • Arapaima'Locally extinct'

    A giant fish which used to dominate the Amazon river is now absent in many areas


  • DragonflyRapid reactions

    Dragonfly's super quick reactions recorded in slow motion by BBC film-makers


  • Wingless adult male of the midge Belgica antarcticaExtreme survivor

    Antarctic midge's small genome may be an adaptation to its extreme environment


  • Myotis midastactus specimen (previously identified as Myotis simus)Golden discovery

    A bat from Bolivia is described as a new species by scientists


  • Dinosaurs 'shrank' to become birds

    Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, new research shows.

  • Would we starve without bees?

    Honey bees are under threat, and as pollination significantly contributes to the food we eat, what would we do without them?

  • Eggshells may act like 'sunblock'

    Birds' eggs show adaptations in pigment concentration and thickness to allow the right amount of sun for embryos, scientists say.

  • Female shrimps are more aggressive

    Female snapping shrimps are more aggressive than males when defending their territories despite their smaller claw size, a study shows.

BBC iWonder

  • Honey bee close-upInsect intelligence

    Are honey bees as smart as your sat nav?

  • Tyrannosaurus rex skull (c) Mark Williamson / Science Photo LibraryDinosaur dynasty

    One group of dinosaurs survived and their descendants can be seen all around us today


  • Brown rat cluse upRise of the rodent

    Reports of giant, 'super rats' are filling the headlines. But why are we being overrun by rats?


  • Cuckoo portraitHoliday hotspot

    What makes the UK such an attractive destination for visiting wildlife?


There have been 75 solar eclipses and 167 major volcanic eruptions in my lifetime

Nicole Malliotakis on Twitter comments on the events that have happened since she was born by using our personalised Your Life on Earth interactive infographic.

Things To Do

RUN BY THE BBC AND PARTNERS

More Nature Activities >

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.