Photograph by Itsik Marom, Alamy 
Read Caption

The Iranian spider-tailed viper uses its lure to catch various warblers from the genus Acrocephalus. The clamorous reed warbler, Acrocephalus stentoreus, (pictured) is often seen in the Middle East.

Photograph by Itsik Marom, Alamy 

This Snake Pretends to Be a Spider—and Catches a Bird

Scientists who filmed the rare spider-tailed viper in the wild have unlocked the secret of its bizarre tail.

Those with a fear of venomous creatures may not be thrilled to know there's a snake that also pretends to be a spider. 

The rare Iranian spider-tailed viper (Pseudocerastes urarachnoides) waggles a fake "spider"—actually a fleshy lure with leg-like scales at the tip of its tail—to tempt birds within striking distance.  

A team led by biologist Behzad Fathinia of Iran’s Yasouj University observed and filmed the viper hunting in Ilam Province (map) for the first time during a three-year study. (See "New Venomous Snake Found: Death Adder Hiding in Plain Sight.") 

The scientists saw the reptile, camouflaged to blend in perfectly with its rocky surroundings, lying in ambush while wriggling about its make-believe spider.  

When a bird pecked at the lure, the venomous viper made a lightning strike in just 0.2 second, according to findings reported recently in the journal Amphibia-Reptilia.  

Making Heads or Tails 

Until 2001, the viper was known only from a single misidentified specimen collected during a U.S. expedition to Iran in 1968.  

The weird structure on its tail was so unlike anything documented in other snakes that it was written off as a birth defect or an abnormal growth.  

Subsequent specimens revealed the same feature, and scientists formally described the animal as a new species in 2006.  

While scientists had suspected its unique tail was used for luring prey, the team's observations of the dramatic bird captures now confirm this.  

Adult snakes preyed only on migratory birds, most of them warblers, the team found. 

If You're Scared of Snakes, Don't Watch This

Every year, thousands of snakes gather at the Narcisse Snake Dens in Manitoba, Canada.

No local birds were caught, suggesting that resident species may be wise to the viper’s spider trick. 

The new study also revealed the viper starts growing its tail lure after birth, and that it isn’t complete until adulthood.  

It's unknown whether only the adults trap birds, though the team observed younger snakes with undeveloped spider lures catching lizards, Fathinia says. (See "Watch: Bird Mimics Caterpillar [and Other Animal Imposters].") 

Not a Rattle

While the viper's odd tail bears some resemblance to a rattlesnake’s rattle, the team’s findings show they aren’t at all alike.   

“In rattlesnakes, profound anatomical changes such as fusion of vertebrae occur [near the tail], while all tail vertebrae are normal in the spider‐tailed viper,” Fathinia says. 

And whereas rattles are built from hard segments of keratin reinforced each time a rattlesnake sheds its skin, the knoblike “body” of the spider lure is made of soft tissue. (See more amazing snake pictures.) 

The illusion of the spider’s legs is created by elongated scales that grow outward from the tail and become erect during an ambush, creating the lure’s spidery look, the team found.    

Most Elaborate Lure 

“It’s unquestionably the most elaborate predatory lure known in snakes or any other species of reptile that uses prey-luring tactics,” says evolutionary biologist and herpetologist Gordon Schuett of the Copperhead Institute in Spartanburg, South Carolina. (Also see "Praying Mantis Mimics Flower to Trick Prey.") 

Various vipers and other snakes use lures to catch prey, though they're usually relatively simple—the most common being an elongated tail that’s colored white, yellow, or black to mimic a wriggly morsel, notes Schuett, who wasn’t involved in the new study. 

“Tail movement, however, can be quite different among species,” he adds. “Frogs, birds, and lizards are very vulnerable to these lures.” 

A snake that dupes animals into trying to eat a bit of it could be vulnerable itself.  

The study team noticed that the spider-tailed viper’s lure was prone to damage, and, in one case, got pecked clean off.