With nearly 3,000 species of snake in the world, there's bound to be a wide variety of hunting methods among them. But one segment of vipers has a particularly interesting way of catching a meal. They use their tails as bait.
Called caudal luring, the technique is a form of “aggressive mimicry” — when a species uses part of its own body to mimic the prey of the very animals it preys upon. The body part snakes have most readily available is the ends of their tails. Some use their tails to look like worms, luring lizards close enough so the snake can strike. Others use their tails to look like spiders to lure birds into striking distance. It's even suspected that some snake species use their tails to lure insectivorous mammals such as mice.
For instance, the Sahara sand viper (Cerastes vipera) uses its tail to mimic larvae. According to a scientific paper by Harold Heatwole and Elizabeth Davison:
Cerastes vipera buries in the sand leaving only its snout and eyes above the surface. Upon the approach of a lizard, it protrudes its distinctively marked tail above the surface and wriggles it in the manner of an insect larva. Lizards attempting to seize the tail are struck by the snake and eaten. In contrast to many other species which practice caudal luring only as juveniles, in C. vipera the habit occurs in adults.
One snake species that really shows off how similar to an insect a tail can seem is the Southern death adder (Acanthophis antarcticus), which shows off its moves in this video:
Caudal luring is documented most often among vipers and pit vipers. But it has also been witnessed in boas, pythons and other species. Here's a video of a juvenile green tree python demonstrating behavior that may be caudal luring.
It's thought that the luring increases the number of encounters with prey, and thus ups the odds of catching something for dinner. Typically the behavior is only seen in juvenile snakes, which catch smaller insectivorous prey, and the behavior fades as they get older and switch to mammalian prey species that don’t care much for wriggling insects. However, researchers are still studying the behavior, and it has been witnessed in adults. But when adults are doing it, it raises questions: Is the snake luring or is it doing something else?
One of the main challenges of studying caudal luring is simply trying to figure out the uses among different species, and to determine the difference between the wiggling of a tail for luring purposes versus a range of other possible explanations, from defense or distraction to communicating with potential mates. Knowing exactly why a snake seems to be wriggling its tail is key to understanding the behavior and its uses for the species.
Some scientists suggest that caudal luring is the root of how the rattlesnake got its noise-making tail, with the switch from adults using the wriggling tail movement as a predatory strategy to a defensive warning occurring somewhere along the evolutionary journey. However, this is a controversial theory. Only one rattlesnake species has been witnessed using its tail as a lure as an adult: the dusky pygmy rattlesnake.
According to researcher Bree Putman, "The only rattlesnake we know of to use its tail (and not its rattle) for both prey capture and for defense in adulthood is the Dusky Pigmy Rattlesnake (Sistrurus miliarius barbouri). This species has the smallest rattle compared to its body size of all rattlesnakes (Cook et al. 1994), and 50% of adults in a typical population cannot produce sufficient rattling sounds because of the smallness of their rattles (Rabatsky and Waterman 2005a)! So these pigmy rattlesnakes may be similar to what rattlesnake ancestors may have looked and acted like. However, we don’t know for sure and debate continues on how and why the rattle evolved."
Meanwhile, a snake species with a tail very obviously evolved to be used as a lure has finally been filmed successfully capturing prey through caudal luring. The spider-tailed horned viper — featured at the top of the article — has a tail that looks remarkably similar to a fat, juicy spider.
From Biosphere Magazine:
The ‘spider’ is a caudal lure – a form of mimicry that predators use to trick and entice unsuspecting prey within striking range. Other snakes do have caudal lures on their tails, but none can boast such a spider-like appearance. In this case, the lure is made up of soft tissue – very different to the keratin-based tails of the infamous rattlesnake, for example. A swelling creates the body of the ‘spider’, and lengthened scales around this creates the illusion of spidery legs.
The viper uses the "spider" on its tail to attract birds, and interestingly, it's a trick that local birds don't fall for; it's birds migrating through the area that tend to fall for the bait. Here's a video of the viper in action. (Fair warning: Don't watch if you're sensitive to hunting scenes.)
Whether it's a tail that moves like a worm, or one that looks surprisingly like a spider, many snake species take advantage of the tactic of caudal luring to gain their next meal. Next time you see a snake holding perfectly still except for a wiggling tail, you might just be about to witness something interesting!