August 5, 2009—Just as Hercules had the multi-headed hydra to contend with, ocean predators tussle with two-headed sea snakes—or so it appears.
Some sea snake species, such as Hydrophis pachycercos (pictured), have evolved so that sharks and other predators can't tell whether the serpents are coming or going, Johan Elmberg and Arne Rasmussen report in a new study today in the journal Marine Ecology.
(Related: "Relocated Sea Snakes Cross Seas to Go Home.")
When Rasmussen was on a research dive in Indonesia, said Elmberg, who was not on the dive, "he saw a venomous sea snake go head first into a narrow crevice. Then suddenly he was surprised to see the snake pull its head out, as if the snake had been able to very quickly turn around inside the crevice."
Moments later Rasmussen, a biologist with the School of Conservation in Copenhagen, Denmark, realized that the "head" was in fact the tail.
While the yellow-lipped sea krait, a nocturnal, shallow-water snake, had been "probing the reef crevice" for fish, Elmberg, an ecologist at Kristianstad University in Sweden, said, "the tail was slowly writhing back and forth, much in the same way as the head moves on a vigilant and actively searching snake."
Later, after studying 98 preserved specimens of the roughly three-foot-long (meter-long) tropical species at three European museums, the researchers concluded that all yellow-lipped sea kraits have "two headed" tail patterns.
"We think these tail patterns and the writhing movements likely intimidate potential predators by fooling them into believing that the tail is actually the venomous head," Elmberg said.
Since then, in the South Pacific waters of the Solomon Islands and elsewhere, the team has found similar markings in other sea snake species, such as H. pachycercos.
And though Elmberg and Rasmussen haven't witnessed H. pachycercos wagging its tail like a head, they suspect it does.