movement

Sneaky snake fakes out fish prey

By moving a point midway down its body first, the tentacled water snake causes its prey to swim toward the snake’s mouth.“The snake has found a way to use the fish’s escape reflex to its advantage.”

VANDERBILT (US)—The tentacled water snake from southeast Asia has found a way to startle its prey so that the fish turn toward the snake’s head to flee instead of turning away. The fish’s reaction is so predictable that the snake aims its strike at the position where the fish’s head will be instead of tracking its actual movement.

“I haven’t been able to find reports of any other predators that exhibit a similar ability to influence and predict the future behavior of their prey,” says Kenneth Catania, associate professor of biological sciences at Vanderbilt University, who has used high-speed video to deconstruct the snake’s unusual hunting technique.

His observations are published in the online edition of the Proceedings of the National Academy of Sciences.

Catania was initially attracted to the tentacled snake because he says it is the only snake that comes equipped with a pair of short tentacles on its nose, and he was curious about their function.

“Before I begin a study on a new species, it is my practice to spend some time simply observing its basic behavior,” Catania explains.

“The snake forms an unusual J shape with its head at the bottom of the J when it is fishing. Then it remains completely motionless until a fish swims into the area near the hook of the J. That is when the snake strikes.”

The snake may be fast, but often its prey is even faster. Many fish have a special circuit in their brains that initiates escape, which biologists call the C-start. Fish ears sense the sound pressure on each side of their body. When the ear on one side detects a disturbance, it sends a message to the fish’s muscles causing its body to bend into a C-shape facing in the opposite direction so it can begin swimming away from danger.

Using a high-speed video camera, Catania examined the movements of the snake and its prey in slow motion. In 120 trials with four different snakes, Catania observed the fish swim toward the snake instead of away from it 78 percent of the time.

Catania also observed that the first part of its body that the snake moves is not its head, but a point midway down its body, in essence faking out the fish’s C-start response and causing it to swim toward the snake’s mouth.

“Once the C-start begins, the fish can’t turn back,” Catania says. “The snake has found a way to use the fish’s escape reflex to its advantage.”

Catania says he next wants to find out if the snake’s actions are learned or instinctive. To do so, he hopes to obtain baby snakes that have just hatched and videotape their first efforts to catch prey.

The research was supported by a grant from the National Science Foundation.

Read more in Exploration, Vanderbilt University’s online research magazine.

Vanderbilt University news: www.vanderbilt.edu/news.

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