Caudal luring is a form of aggressive mimicry in which a predator uses tail movements to attract prey. The prey animal misinterprets the tail as a worm-like species or another smaller prey. Once the prey animal is within striking range, the predator attacks. Snakes, often juveniles, and some types of shark are the main species that practice caudal luring. The mimicry was initially interpreted as a warning sign displayed under stressful circumstances. The study of the tail movements suggested that the behavior evolved from tail vibration. Researchers have also used different experiential paradigms to investigate stimulus control and visual deception in snakes.
Mimicry
The tail of a species may serve various functions, such as aggression, defense and feeding. The caudal luring behavior was first recorded in 1878 and is an instance of aggressive mimicry. Predators attract their prey by moving their caudal section in a way that mimics the victim's own prey. The prey is intrigued by caudal behavior and will investigate assuming it is their own prey.
Species
Snakes
Caudal luring behavior is found in over 50 different snake species. It is most common in boas, pythons, tropidophiids, colubrids and elapids of the genus Acanthophis. It is, however, the most obvious in vipers and pit vipers, especially in rattlesnakes. As the snake is waiting for its prey, it is coiled up and has its distinctively marked tail elevated, visible and moving in a way that captures the attention of its prey. Once the prey is in striking range, the snake captures the prey. Due to the tail resembling a writhing caterpillar and another worm-like insect larvae, the tail of the snake is often referred to as a vermiform. One elaborate example of caudal luring occurs in the spider-tailed horned viper, which employs a highly modified tail to mimic a spider's form and locomotion. Caudal luring is more frequently observed in juvenile snakes. Of the snakes that practice the caudal luring behavior, 80% of the snakes are juvenile. The tails of juvenile snakes are often a vibrant color, making them difficult to ignore. As the juvenile snakes mature into adulthood, their tail color will become consistent with the rest of their body. Juvenile snakes have a smaller lure compared to the size of an adult's lure. Studies show that a smaller lure is more effective in attracting prey, as it is closer to the size of the worm-like prey. This may explain why caudal luring is more often seen and successful in younger snakes.
Sharks
Caudal luring is found in some sharks, being common among three species: Alopias vulpinus, Alopias superciliosus and Alopias pelagicus; they have tails of varying shapes, but they all use them to attract and then immobilize prey. The tasselled wobbegong a carpet shark, has a caudal fin resembles a small fish with a small dark eyespot; this is waved slowly to attract prey.
Other
Caudal luring behavior is believed to occur in pelican eels.
Evolution
It has been suggested that caudal luring was involved in the evolution of the tail vibration rattle of rattlesnakes, a warning signal and a way of auditory communication, though this has been challenged. Prey luring, in general, is confounded by false interpretation, as the wiggling of an appendage could have other behavioral meanings including aposematism, defence, or nervous release, and experimental evidence has been weak. Caudal luring is thought to have evolved from a caudally localized intention movement. Essentially, the act of remaining stationary while sensing prey produces general nervous system excitation that gets released in the form of tail movements. Caudal luring is not merely tail undulations, but must specifically be attractive to prey. Caudal distraction is another behavior used by snakes, and the tail motions are similar to caudal luring. The difference is in the snake's posture and especially in the nature and outcome of the behavior in reference to the encounter with prey. Other caudal luring-like movements occur as warning signals and are induced by stressful circumstances.
