Spiders eat snakes around the world, shocking study reveals

North American widow spiders, not tropical tarantulas, have a particular taste for reptiles, according to a sweeping analysis of data across six continents.

Published 24 Jun 2021, 10:22 BST
Wandering Spider
A large wandering spider preys on a snake in Peru's Amazon rainforest.
Photograph by Anton Sorokin / Alamy Stock Photo

Could a spider kill and eat a snake?

The question might sound like a playground hypothetical, but it’s the topic of a new study published in the Journal of Arachnology. The answer is a resounding yes—so much so that even the scientists who conducted the study were stunned by their results.

“I was surprised that snake-eating by spiders can be found on all continents (except Antarctica),” says study leader Martin Nyffeler, a spider expert at the University of Basel in Switzerland. “I was surprised that so many different spider groups are capable of killing and eating snakes. I was surprised that so many different snake species are occasionally killed by spiders.”

“All of this was unknown before,” says Nyffeler in an email.

In all, Nyffeler and his co-author, University of Georgia snake expert J. Whitfield Gibbons, scoured every piece of scientific literature they could find, as well as social media sites, news coverage, and even old issues of National Geographic, to unearth more than 300 observations of spiders killing snakes. The data encompassed more than 40 spider species and more than 90 snake species.

A black widow preys on a snake in New River Gorge National Park in West Virginia.
Photograph by Julia Statler

As you might expect, large spiders such as tarantulas were among those most likely to take on a reptile. But they weren’t the snake-eating champs. Instead, a spider family known as the theridiids, which includes black widows and their kin, were responsible for capturing the most snakes. Even more curious, the vast majority of these reports happened not in the tropics, but across North America(Read about the first documented case of a tarantula eating a snake in the wild.)

The research also significantly expands our knowledge of spider predation, which could play a bigger role in the balance of the ecosystem than previously thought, Nyffeler adds.

“All spiders of the world combined would weigh an estimated 25 million tons, and they would kill about 400 to 800 million tons of prey per year,” he says. “To fully understand the spiders’ important role in the balance of nature it is crucial to understand the entire spectrum of their feeding habits.”

How spiders attack

On average, the snakes preyed upon by spiders are small—usually around just 10 inches in length. But even these little serpents are many times the size of the arachnids, which averaged body lengths of less than half an inch. (See 8 pictures that will make you love spiders.)

In most cases (such as the theridiids), these itsy-bitsy spiders build extremely tough webs, which often extend to the ground and ensnare unsuspecting snakes. Once caught, the spider delivers its venomous bite to paralyse its victim, wraps the snake in silk, and hauls it aloft to dine. Digestive enzymes in the spider’s bite liquefy the snake’s soft parts, just as they would with a fly. The spider then takes its time slurping up the insides, with some meals stretching out days and even weeks.

“Even though I talk all the time about how strong spider silk is, I think I was still underestimating this incredible material,” Sebastian Echeverri, a spider scientist and editor of Arachnofiles, said by email. “I kind of assumed that a snake could rip their way out and get to safety. Snakes are basically all rock-hard ab muscles!” 

Around 30 percent of the snakes were also venomous, such as the New World coral snakes, Australian brown snakes, rattlesnakes, and Neotropical lancehead snakes. But what good is venom when your foe is too small to pierce with a fang?

Watch how the world's biggest spider immobilizes its prey – and keeps predators at bay
With a leg-span nearly a foot wide and a very particular defence mechanism, Goliath bird-eaters are truly lethal hunters. Footage from the show "World's Weirdest".

“There’s no easy way for a rattlesnake to defend itself with venom against a spider,” says Emily Taylor, a snake biologist and director of the Physiological Ecology of Reptiles Laboratory at California Polytechnic State University.

Good (snake) Samaritans 

Because so many of the incidents occurred in the wild and were observed by ordinary people, the scientists analysed another trend—when humans intervene.

Out of 319 spider-vs.-snake occurrences, the spider succeeded in killing the snake 87 percent of the time. In 1.5 percent of the incidents, the snake escaped on its own. But 11 percent of the time, people stepped in to save the serpents.

Even in Australia, where most standoffs happen between brown snakes and redback spiders—two species lethal to humans—there were occasions when people not only freed the snakes but cleaned them of cobwebs before setting them free.

“Given that most humans despise both spiders and snakes, it is very surprising to me that there are humans willing to rescue a snake,” says Nyffeler, who himself suffers from a “severe snake phobia.” (Learn whether we’re born fearing snakes and spiders.)

Given the arachnids’ more diverse diet, the study could also inspire further investigation into how their venom works.

“While we now understand quite well how black widow toxins are affecting vertebrate nervous systems, we still poorly understand the mode of action of the toxins of many other spider families,” he says.

Overall, the study is “really provocative,” Taylor adds, because it features two animals that many people fear.

“For most people in the world, this would be their worst nightmare. Eight legs against zero legs,” she says. “But for me, this is like my wonderland.”

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