After painstakingly analysing thousands of hours of video footage, two Wits University researchers have shown that puff adders actively lure their prey into striking range using their tongues.
The new discovery comes after researchers Xavier Glaudas and Graham Alexander confirmed that the adders use "lingual luring" to attract amphibian prey.
The duo, who were funded by the National Geographic Committee for Research and Exploration, tracked 86 puff adders over three years at the Dinokeng Game Reserve, about 100km north of Johannesburg.
Glaudas, a herpetologist and postdoctorate fellow at the Alexander Herpetology Laboratory at Wits, said that a puff adder's strike is typically no longer than 10cm in distance.
"So it needs a strategy to attract potential prey to come within that striking range in order to catch it," he said.
Glaudas said their research showed that puff adders positioned their tongues to resemble an invertebrate animal that frogs feed on, thus attracting them to the snake.
Distinguishing between prey
Even more surprising was the fact that the snakes only used lingual luring to attract amphibian prey.
"All the cases of lingual luring that we have observed, occurred with frogs, which suggests that puff adders are able to distinguish between amphibian prey and other prey like small mammals," Glaudas said.
Glaudas captured wild snakes and tracked them by surgically implanting radio transmitters into the snakes and releasing them at their place of capture.
"We really wanted to have a closer look into the secretive lives of these fascinating animals, and specifically study their foraging ecology," he said.
To aid their research, Glaudas and Alexander set up video cameras in front of puff adders lying in ambush position.
"We placed our cameras mounted on a tripod about 70cm away from the snake, and the camera continuously recorded what was going on. We came back the next morning to get the memory cards and reviewed everything that happened during the night," said Glaudas.
Findings 'complete luck'
The researcher said they gathered more than 4 600 hours of video footage of snake foraging, amounting to around 193 days of continuous footage.
Glaudas said that even though they knew snakes used their tongues to pick up scent cues, what they saw during their research was "complete luck".
"We know that snakes use their tongues to pick up scent cues in their environment, but these snakes were extending their tongues out of their mouths for up to 30 seconds, which is dramatically longer [than] what they do when they are just using their tongues to 'smell' their environment."
Glaudas said researchers know that several species use tongue luring to attract prey.
"Some wading birds, like egrets, do it, as well as alligator snapping turtles and some aquatic snakes, but this is the first time that it is reported in a terrestrial snake."
The researchers found that puff adders also used the waving of their tails as lures. However, none of the tail luring behaviour attracted prey within the camera's field of view.
"We suspect that this behaviour is also used to attract prey as it is pretty common in snakes, including adders, but we weren't able to observe prey capture with the videos," Glaudas said.