The spider-tailed horned viper (Pseudocerastes urarachnoides) is a species of viper, a venomous snake, in the family Viperidae and genus Pseudocerastes. The genus is commonly known as "false-horned vipers".[3]
The species is endemic to western Iran[4] and over the border region with Iraq. It was originally described by scientists as Pseudocerastes persicus, attributing the tail to either a parasite, deformity, or tumors. Another specimen was found in 2003.[5]P. urarachnoides was officially 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 with a bulb-like end that is bordered by long drooping scales that give it the appearance of a spider.[4] The tail tip is waved around and used to lure insectivorous birds to within striking range.[6]
Etymology
The specific name, urarachnoides, is derived from Ancient Greek (οὐρά + αράχνη + οειδής), and refers to this snake's spider-like tail-tip, as does the common name, spider-tailed horned viper.[4]
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.[8]
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.[9]
Distribution and habitat
The species is found in the western parts of Iran and over the border into the eastern part of Iraq. It is found in the Zagros Mountains, more commonly on the western side of the mountains. Its current range is relatively small and getting smaller.[10] This species lives in higher elevations that are primarily composed of gypsum. It prefers deep cracks and holes within the rock. They use these areas because they trap humidity and moisture during the hot summer months. During the day, it is most commonly found in the shade of a shrub.[11]
The snake's conspicuous tail contrasts with the rest of its body, which is well-camouflaged with disruptive colorationUsing the tail as a lure and catching a wren-like bird
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.[4]
The venom of Pseudocerastes urarachnoides mainly acts as a cytotoxin. It targets cells and destroys them. Unlike its sister species, this cytotoxin destroys a wide variety of cell types. It has minor neurotoxic effects. This venom works as a procoagulant, with a remarkable coagulation speed, with reports of about 13 seconds before coagulation.[14] Compared to its sister species, this venom is highly-specialized for birds. The venoms of the sister species, P. fieldi and P. persicus, do not have significant effects on birds and are more suited for mammals and amphibians. P. urarachnoides has a significant effect on birds, mammals, and amphibians. There is speculation that the venom affecting amphibians, toads specifically, could be a sign that these are the main diet of the young snakes, though more information about the juveniles still needs to be collected. In a study by Brouw (2021), it was found that the venom of this species does have a coagulant effect on humans and affects the human's Factor X. However, there has never been a recorded case of human envenomation in the wild. The severity of the effects that this venom would have on humans is not known.[14]
^Bostanchi, H., Anderson, S., Kami, H., & Papenfuss, T. (2006). A New Species of Pseudocerastes with Elaborate Tail Ornamentation from Western Iran (Squamata: Viperidae). Proceedings of the California Academy of Sciences, Volume 57(No. 14), 443-450.
^ abFathinia, Behzad; Rastegar-Pouyani, Nasrullah; Rastegar-Pouyani, Eskandar; Todehdehghan, Fatemeh; Amiri, Fathollah (2015). "Avian deception using an elaborate caudal lure in Pseudocerastes urarachnoides (Serpentes: Viperidae)". Amphibia-Reptilia. 36 (3): 223–231. doi:10.1163/15685381-00002997.
^Fathinia B., Rödder D., Rastegar-Pouyani N., Rastegar-Pouyani E., Hosseinzadeh M. & Kazemi S. (2020) The past, current and future habitat range of the Spider-tailed Viper, Pseudocerastes urarachnoides (Serpentes: Viperidae) in western Iran and eastern Iraq as revealed by habitat modelling, Zoology in the Middle East, 66:3, 197-205, doi:10.1080/09397140.2020.1757910
^Anderson, S. C. (2002). An introduction to the literature of the vertebrate zoology of Iran. Zoology in the Middle East, 26(1), 15–28. doi:10.1080/09397140.2002.10637917
^Knapper, Emma (director and writer); Oldroyd, Adam (writer); Attenborough, David (star); Drost, Peter (star) (3 November 2019). "Asia". Seven Worlds, One Planet. BBC One.
^ abBrouw, Bianca, et al. "Extensive Variation in the Activities of Pseudocerastes and Eristicophis Viper Venoms Suggests Divergent Envenoming Strategies Are Used for Prey Capture." Toxins, vol. 13, no. 2, Feb. 2021, p. 112. Crossref, doi:10.3390/toxins13020112.
