Snake uses odd tentacles to sense prey
American biologists have found that an unusual snake with short tentacles on its snout uses the appendages to locate its prey, even in the dark.
The snake, Erpeton tentaculatus, is an aquatic snake that lives in murky lakes and rivers in Southeast Asia and specializes in hunting fish.
The snake has two tentacles, about a half-centimetre long, projecting out either side of its snout.
"They're very flexible, and that's sort of a clue as to what's going on with them. They're extremely sensitive to water movements," Ken Catania of Vanderbilt University told CBC Radio's Quirks & Quarks.
The snakes hunt by suspending themselves in the water in a distinctive J-shape and waiting for fish to get close. The snake then fools the fish into swimming into its mouth.
"What the snakes do is startle fish by moving a small portion of their body so that they turn toward their strike, and the whole thing happens in about a 40th of a second," said Catania.
To test whether the snakes hunt by sight alone or used other senses, the scientists designed experiments to separate the senses.
"We presented the snakes in a test where there was a simulated digital fish below a glass barrier at the bottom of the aquarium and looked to see in the complete absence of any water movements, could these snakes strike accurately, and they could," said Catania.
Another test removed the snakes' sense of sight by using infrared lighting, which the snake can't see, to observe the snake as it hunts fish.
"And, sure enough, they can catch fish without their eyes," Catania said.
Measured electrical ability
The researchers suspected that the tentacles could be responsible for this ability, and to test it, they measured the electrical activity in the nerves of the tentacle.
"When we did that, we found that they are just incredibly sensitive to the slightest touch," said Catania.
The nerves in the tentacle could react to the most subtle stimulus the scientists could create, so they couldn't even determine a lower limit to their sensitivity.
They then measured the neural activity of the tentacle while creating vibrations in the water several centimetres away and found that they were sensitive to those movements, too.
"The fish are relatively close to the tentacled snake as the snake is waiting to strike. These fish are definitely producing water movements in the same range that we stimulated with," said Catania.
The scientists were also able to measure nerve activity from the tentacles in the part of the snake's brain called the optic tectum, which receive signals from the eyes and other sensory organs, suggesting that the tentacle movements and visual information are being co-ordinated.
"There's good evidence from that that they are not only using both, but integrating the two senses together as they're trying to determine exactly where the fish is," said Catania.
Catania isn't sure how the tentacles could have evolved, but has a good "guess," as he put it.
"They seem to be positioned exactly where the pit organs in pit vipers are found on the front of the face. Pit organs are infrared heat-sensing organs that are used to detect warm-blooded prey, such as rodents. It does make you wonder if there is some sort of precursor, a very sensitive area of heavily innervated tissue on some of these ancestral snakes that might give raise to various sensory organs," he said.
The research was published this month in the Journal of Experimental Biology.