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Fears of snakes and spiders are among the two most common phobias reported. For those who suffer from them, the spider-tailed viper (Pseudocerastes urarachnoides) must seem like a nightmare incarnate.
While this unusual snake was described in 2006, researchers first encountered a specimen back in the 1960s in the deserts of western Iran. Given the strangeness of its tail and the lack of other similar vipers, it was assumed to be a tumour or some other deformity. It was only with the discovery of other spider-tailed vipers that scientists realised this was an unknown species.
The hypothesis that the tip of the tail functions as a lure has been supported by laboratory observations. When a chick was placed in the same enclosure as the viper, the viper began to twitch its lure. After half an hour the chick approached the "spider" and began to peck at it. The snake drew its tail towards its head and the chick followed, whereupon it has promptly bitten by the snake and died an hour later. Subsequent observation with a sparrow had the same result (though this time the snake twitched the lure right in front of its head).
It's thought that the snake exhibits the same ambush behaviour in the wild. Its mottled brown, rough scales allow it to blend in with its environment (burned gypsum in sunlight) and locals believe it can climb trees. It's known the viper eats birds, but it's also suggested it eats small reptiles and mammals.
Tail (or caudal) lures are not uncommon among snakes, but they're rarely this elaborate. Usually the lure is simply a thin tip that moves like a worm (as in the case of Australia's northern death adder). It's unknown why the spider-tailed viper has evolved something so ornamental when worm-shaped lures work so well.