Mystery of the Spider-Tailed Viper Unraveled

To some people it might sound nightmarish: an animal that looks and moves like a snake at the front - and like a spider at the back. In fact, there is such a dual creature: the spider-tailed viper. Its end - a knob with leg-like appendages - consists of deformed scales, as a research team reports in the journal The Anatomical Record.

Like many other animals, the spider-tailed viper relies on so-called mimicry, the imitation of characteristics of other species for purposes of deception, in the fight for survival. A classic example are harmless hoverflies, whose yellow-black markings resemble defensive wasps and are intended to drive away potential enemies.

The viper living in Iran with the technical name Pseudocerastes urarachnoides, on the other hand, does not want to scare off, but rather attract - namely birds. They should mistake the appendage on the tail for a spider. If they approach in the hope of a tasty morsel, the snake will snap and the bird itself becomes a meal.

Intrigued, the team led by Georgios Georgalis from the Polish Academy of Sciences in Krakow took a closer look at the spider dummy - with surprising results: the viper's CT scan showed no changes to the tail bones.

“In some other snakes, such as sand boas and rubber boas, the vertebrae at the tip of the tail have extreme shapes that look really alien,” Georgalis explained. In the case of the spider-tailed viper, however, there is absolutely nothing in the skeleton that indicates how extreme its tail looks from the outside.

For him as a paleontologist, this was a very frustrating result, explained Georgalis. Prehistoric life may also often be much stranger than the bones alone suggest. “We deal with beautiful animals, but most of the time we're trying to put together puzzles where some pieces are missing, and in the end we can't be 100 percent sure what the animal actually looked like.”

A first specimen of the spider-tailed viper was collected and prepared in 1968, explained co-author Ruane from the Field Museum in Chicago. However, it was assumed that the animal had a deformity or a tumor. “It sat on the museum’s shelves for decades, but it wasn’t until another specimen with a similar tail was found in 2003 that it was examined again.” In 2006, the snake was officially described as a new species.

Video footage later showed the snake using the spider-like appendage on the tip of its tail as bait to attract birds. It moves the end of its tail back and forth over the ground - even to human observers, it can look like a spider is busy running back and forth.

Ruane explained that she saw the snake herself in the wild as a doctoral student. “The appendage on the end of her tail is so incredible, I remember thinking it was really cool,” enthused the assistant curator of herpetology (amphibians and amphibians). “It’s my favorite specimen in the museum; I use it all the time during demonstrations and tours.”