In the rocky scrublands of western Iran and eastern Iraq, a cunning predator relies on masterful mimicry to capture its prey. The spider-tailed horned viper, or Pseudocerastes urarachnoides, is a venomous snake whose tail has evolved to look like a spider. The snake's tail shares a close resemblance to an arachnid to attract its prey, which are most often birds.

This viper hunts by hiding in rocky crevices, revealing only its tail above the surface. Featuring a bulbous end fringed by long scales, the tail is skillfully made to "crawl" on the rock, perfectly mimicking a spider. Birds, deceived by this convincing display, swoop down for an easy meal -- only to become the viper's next victim.

Initially spotted in the Zagros mountains of western Iran, it was later found in similar habitats across the border in Iraq. The scientists who first spotted the snake mistook it for a Persian horned viper with a deformed or tumorous tail. In fact, you would have found a wrongly labeled specimen of the snake in the late 1960s at the Field Museum of Natural History, Chicago.

It was as late as 2006 when Pseudocerastes urarachnoides was finally described. Since then, no more than 30 individuals have been seen by humans.

Many snake species around the world are known to have similar highly evolved tails. The rattlesnake (also a viper), for example, makes one of the fastest movements among vertebrates with its tail.

It vibrates loosely connected keratin scales to produce a bone-chilling rattle that warns predators to stay away. It can even achieve various frequencies, getting higher as predators venture closer, like an alarm.

The spider-tailed horned viper, however, is thought to have one of the most intricately evolved tail among all snakes.

It can be seen on rocks and in bushes, looking for insectivorous birds like larks, warblers and even raptors like falcons. Aside from offering a hiding place while hunting prey, rocky crevices also provide much-needed humidity and solace during the hot summer months.

This snake is sometimes referred to as a false-horned viper on account of the scales on its head that form two "horns". These aid in its already expert camouflage, distorting the outline of its head to confuse prey. Many desert vipers are noted to sport horns on their heads, like the Saharan horned viper and horned adder. Meanwhile, snakes that dwell in forests tend to evolve horns on their noses, like the Gaboon viper.

The venom profile of this viper is daunting -- it is cytotoxic, being able to kill a wide range of cell types. Its venom is so powerful that it takes only 13 seconds to coagulate its prey, leading to uncontrollable internal bleeding that is ultimately fatal.

Although the viper's venom has evolved to target birds, it can still be fatal to humans. The coagulating effects of the Iranian spider-tailed horned viper's venom are similar to those of the Russell's viper, one of the deadliest snakes in the world. However, no human bites have ever been recorded from this species, according to a 2021 study in Toxins.

Scientists can only make guesses on the effect the venom would have on people, as observed in the study. The results showed that, in minor cases, victims of envenomation could experience vomiting and fever. Higher doses of the venom could lead to blood clotting disorders, kidney failure and death. Some neurological symptoms like confusion, dizziness, migraines and seizures may also be expected.

The viper is currently known from a small geographic distribution, but a lack of research in eastern Iran may be leaving us in the dark about its actual range size. We know so little about its ecology -- population sizes haven't been estimated yet, though it is assumed to be dwindling fast, according to a June 2020 paper published in Zoology in the Middle East.

Despite wildlife trade being illegal, social media has been used in Iran for the trafficking of the snake. In 2018, evidence emerged that ten individuals had made their way to German pet-keepers. Scientists are calling for more research on this endangered species to tailor conservation efforts.