Page last updated at 09:00 GMT, Thursday, 6 August 2009 10:00 UK

Sea snake's two-headed illusion

Researcher and sea snake (Arne Rasmussen)
Dr Arne Rasmussen discovered the sea snake's secret

Venomous sea snakes use skin markings and movement to fool predators into thinking their tail is a second head, according to a study.

Scientists found that the yellow-lipped sea krait twists its tail, giving the illusion of having two heads and a double load of deadly venom.

The team published their work in the journal Marine Ecology.

They believe this two-headed mimicry has evolved to protect the sea snake from attack while it searches for prey.

Despite being extremely venomous, the snakes are vulnerable to a number of predators, including larger fish, sharks and birds.

Arne Rasmussen, from the Royal Danish Academy of Fine Arts' School of Conservation in Copenhagen, Denmark, led the study.

He and his team studied the snakes whilst diving off the coast of Bunaken Island in Indonesia.

They followed the kraits as they were swimming between corals and crevices hunting for food.

Dr Rasmussen noticed the two-headed illusion when he spotted one snake with its head apparently facing him while it probed the coral with its tail.

The snake's second head then emerged from the coral and he realised that the first head he had seen was actually a tail.

Dr Rasmussen and his colleagues then examined almost 100 sea kraits from three major museum collections in Paris, Berlin and Copenhagen, while also monitoring the behaviour of the wild snakes during an expedition to the Solomon Islands.

This research confirmed that each sea krait species had a distinctive colouration pattern - a bright yellow horseshoe marking on the tip of both the head and the tail, and similar patterns of black markings.

"This may increase the chances of (the snakes) surviving predator attack by exposing a less 'vital' body part," explained Dr Rasmussen.

"But more importantly it may deter attack in the first place if [predators] perceive the tail as the venomous snake's head."



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