A deadly trap for birds and a surprise for scientists the secret of the optical illusion in the tail of the Iranian snake

This snake, which lives in the arid, rocky regions of western Iran, is one of the strangest known examples of an animal using a part of its body to deceive its prey. When it lies motionless among the rocks, it moves the tip of its tail in a way that mimics a small spider crawling on the ground. As soon as a bird approaches, hoping for an easy meal, the roles are quickly reversed, and the hunter becomes the prey, with the snake striking.

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Georgios Georgalis, the study's lead author and an associate professor at the Institute of Zoology and Animal Evolution at the Polish Academy of Sciences in Krakow, says the researchers expected to find something quite different inside the tail. He explains that the spider-like appearance "is limited to the external shape," while the tail vertebrae themselves looked typical of snakes, and the skeleton bore no obvious markings that would reveal how unusual the tail was from the outside.

The story of this snake began nearly six decades ago; in 1968, scientists acquired a specimen that later ended up in the Field Museum in Chicago. The tip of its tail was so unusual that researchers initially thought it might be a deformity or a tumor. The specimen remained in the museum's collections for decades, until in 2003 another snake with the same peculiar tail was discovered.

He explains that the bulging tail tip, surrounded by long scales, not only resembles a spider in shape, but becomes even more convincing when the snake begins to move it. This trick is known as "tail lure," meaning using the tail to attract prey rather than pursue it. In this snake's case, the bird is attracted to what it mistakes for a spider, only to discover too late that the "spider" is merely part of a hidden predator.

Computed tomography (CT) scanning allowed researchers to capture a large number of X-ray images from different angles and then combine them into a three-dimensional model of the inside of the body. According to Gorgios, this was a crucial advantage because the specimen the team examined was not just a preserved snake, but the official reference specimen of the species; therefore, cutting it open or dissecting it would have resulted in the loss of irreplaceable scientific data.

The researchers had a clear reason to expect unusual vertebrae; in some snakes, such as certain types of sand boas and rubber boas, the vertebrae near the end of the tail take on specialized shapes related to the way the tail is used; therefore, it seemed logical that a snake that evolved with a tail capable of mimicking a spider would have similar skeletal changes.