Spider-tailed horned viper
The spider-tailed horned viper ("Pseudocerastes urarachnoides"), also known as spider-snake, is a species of viper, a venomous snake in the family Viperidae and genus "Pseudocerastes". The genus is commonly known as "false-horned vipers". The species is endemic to western Iran and over the border region with Iraq, and was originally described in 2006. The head looks very similar to that of other "Pseudocerastes" species in the region, but the spider-tailed horned viper has a unique tail that has a bulb-like end that is bordered by long drooping scales that give it  the appearance of a spider. The tail tip is waved around and used to lure insectivorous birds to within striking range. Etymology. The specific name, "urarachnoides", is derived from Ancient Greek ( tail + spider + like), and refers to this snake's spider-like tail tip, as does the common name, spider-tailed horned viper. Description. Like other vipers in the genus "Pseudocerastes", the scales above the eyes rise up to give "P. urarachnoides" a horned appearance. A specimen had been collected in 1968 as part of the Second Street Expedition to Iran and deposited in the Field Museum of  Natural History at Chicago, identified as "Pseudocerastes persicus". It was, however, found to be distinct, and it was described as a new species in 2006. The species is distinguished by a number of characteristics. There are about 16 to 17 scales between the horns, and the scales on the body above are rougher than on other species in the genus. There are 15 pairs of subcaudal scales, and the scales on the sides of the tail are elongated and appear like appendages of an arthropod. The tip of the tail is inflated into a bulb-like shape. Mimicry and behaviour . The snake is a superb mimic. The tail resembles a spider or other arachnid, and the authors who described the species speculated that it was used as a lure to attract birds, as a digested lark had been found in the stomach of the paratype specimen. The tip of the tail is used as a lure in several other species of snake, including "Bitis caudalis", "Crotalus cerastes", "Sistrurus catenatus", "Agkistrodon contortrix", "Acanthophis antarcticus", "Acanthophis praelongus", and "Morelia viridis", but none of these examples has the unique elongated scales that give it the appearance of arthropod appendages. The actual use of  the tail to lure birds (an example of caudal luring) has been confirmed in field studies; the tail is moved in a figure-of-eight pattern. Footage of the spider-tailed horned viper using its tail to lure a migrating bird featured in the Asia episode of the BBC series "Seven Worlds, One Planet" narrated by David Attenborough. Distribution. This species overlaps in distribution with "P. fieldi" in Gilan-e Gharb, next to Qasr-e Shirin, Kermanshah, and with "P. persicus" in Bina and Bijar, Ilam Province. Taxonomy. Molecular studies based on cytochrome b show it to be closer to  Pseudocerastes persicus than to "P. fieldi".