Picture a mythological beast, a half-snake, half-spider hybrid, likely to make both arachnophobics and herpetophobics sleepless. Imagine its tail, from which eight mutant legs stick out, and where several small, black and shiny eyes open up to scrutinize their prey. It could well be a lovecraftian horror fantasy, or a new incarnation of the alien from The Thing.
And yet, such an animal exists. Even if reality is, of course, not so dramatic.

In 1968, William and Janice Street were exploring Iran. It was their second naturalistic expedition on behalf of the Field Museum of Chicago (in the following decade they would carry out three more, in Afghanistan, Peru and Australia), with the aim of expanding the Museum’s collection with new specimens. Their mission was mainly focused on mammals, but during their trip the Streets were also collecting several reptiles.
One day they noticed a snake which seemed to have a solifugid — a type of arachnid living in arid and sandy regions — attached to its tail. Once brought back to the Museum, the specimen was examined by researcher Steven Anderson, who realized the alleged spider was in reality a part of the viper’s own morphology: since only one specimen was known, he speculated that either a tumor, a congenital defect or a parasite could be responsible for that strange appendage. The snake was identified as Pseudocerastes persicus, the persian horned viper, and almost forgotten in the shelves of the Museum for nearly fourty years.

Then, in 2003, researcher Hamid Bostanchi came in possesion of a second specimen, identical to the one previously classified. He thus began suspecting the mutation was more than a physical defect, given that 35 years had passed from the first finding. He was therefore the first to speculate that this was an unknown species.
A third specimen was found in the poisonous animals section of the Razi Institute in Karaj, Iran: it had been mistakenly classified as a horned desert viper.
At this point Bostanchi, together with the first discoverer Steven Anderson and other collegues, published his findings and baptized the new snake Pseudocerastes urarachnoides (“with a spider-like tail”) in a 2006 essay.

X-rays showed the caudal vertebrae, bearing no sign of malformation, extending well into this anomalous structure, which was evidently formed by modified scales. As many vipers move their tails to lure preys, Bostanchi hypotesized that this bizarre spider-shaped protuberance was nothing else than an elaborate hunt bait.
In 2008 a live P. urarachnoides was captured and the animal, held in captivity, seemed to actually use its tail to lure sparrows and baby chickens near him; then, with a sudden twitch, it bit them and poisoned them in less than a half second. In its stomach fowl remains were found, indicating that this bait could have evolved specifically to catch birds.

To clear any doubt and verify the hypothesis, other observations followed, also in a natural environment. Here is a recent and wonderful video of the spider-tailed viper using its caudal bait to deceive and catch a bird.

If a viper imitating a small arachnid might seem an exceptional case of mimicry, what’s really astonishing is that in nature a perfectly specular example can be found: an insect, that is, mimicking a snake.
It’s the Dynastor darius, a butterfly which during its pupa stage locks itself inside a chrysalis that would definitely look far from tempting to a possible predator: in fact, it resembles a reptile’s head.

The pupa is still aware of the world outside the chrysalis, and if it feels threatened it can shake its “mask” from side to side, to make it even more convincingly realistic.

Sometimes it is asserted that man is the only animal capable of lying.
Yet, from crypsis to mimicry, it’s clear that fiction and deceit are extremely widespread behaviors among the rest of living creatures: they are weapons of attack and self-defense, sharpened in time. The predator has to disguise its presence, the prey has to dupe the senses of its enemy, and so on, in a constant game of mirrors in which nothing is really as it seems.