Snakey sense … tingling!
Just as Spider-man has his spidey sense to warn him when danger’s near, the bizarre tentacled snake has its own special system for sensing an approaching meal, a new study says.
"When I first saw these things in … [a] zoo I thought, What the heck? They were an irresistible mystery," said study leader Ken Catania, a biologist at Vanderbilt University in Tennessee.
Catania and colleagues observed that the tentacled snake hunts in a strange way: It forms a J with its body, slightly moving its lower midsection when fish swim by. This movement usually causes a fish to dart in the opposite direction, straight toward the snake’s mouth.
Even after figuring out the snake’s technique, the scientists were left wondering what the tentacles were for.
"We suspected they were fish detectors, as the snake is unusual in specializing almost completely on fish as prey," he said.
To solve the mystery, Catania and colleagues first marked tentacle nerve fibers of dead snakes with fluorescent dye and viewed them under a microscope. The team found that many nerves crossed the centers of the tentacles rather than at their surfaces. (See related pictures of glowing animals.)
That finding was intriguing: Nerve cells associated with senses such as taste and touch are not usually so deeply embedded. The structure suggested that these nerve cells were positioned to sense movement of the entire tentacle rather than detailed surface sensations, the study says.
In another experiment using live snakes, the team stroked the appendages with tiny hairs while simultaneously monitoring electrical activity in the snakes’ brains.
They also found that the tentacles sensed even the smallest movements of water generated by a nearby vibrating sphere, suggesting the tentacles would also respond to similar movements made by nearby fish.
Following the nerve signals, the team noticed that touch signals from the tentacles ran to a part of the brain that registers vision, meaning that the two senses—touch and vision—work closely together in the tentacles.
Special Snake Sense
As a final test, Catania put fish in the tank with the snakes, turned off the lights in the laboratory, and monitored the snakes—which have perfectly good eyesight—with infrared cameras. The predators caught fish in total darkness with no trouble.
“It may seem a bit odd to have both good eyesight and this special tentacle sense, but really, it isn’t that rare to have predators with two very good senses,” Catania said.
"Just look at barn owls—they have great sight and great hearing that they use differently based upon lighting conditions," he said. "The snakes seem to be similar, with their tentacles probably being the greatest help at night."