When Spiders Hunt Snakes for Dinner

A spider and a snake meet in the woods. Who comes out alive?

Don’t always put your money on the snake. Venomous spiders can prey on snakes much larger than they are, a new study finds. 

Study senior author Martin Nyffeler dug through years of scientific literature and uncovered 319 observations of spiders killing snakes. The records included more than 90 snake species and more than 40 spider species. The results are published in a new study in the Journal of Arachnology.

Nyffeler is an arachnologist and senior lecturer in zoology at the University of Basel in Switzerland. He was searching journals for information on spider prey data with a focus on spiders as the natural enemies of insects.

“But I was also collecting data on unusual feeding behaviors such as feeding on vertebrates or plant materials. Over the years I collected a huge number of spider prey records including numerous accounts of spiders feeding on snakes,” Nyffeler tells Treehugger.

He also began searching the internet for cases of spiders preying on vertebrates. And in some cases, he also collected information from citizen scientists.

“I was very surprised that snake predation by spiders is so common and widespread—both geographically and taxonomically,” he says.

Most Prolific Snake-Eaters

The snake-eating champs were a family of spiders known as theridiids, which include black widows and their relatives. The second-best snake catchers were those in the tarantula family and the third were members of the orb weaver clan.

These are all typically large spiders, relatively speaking, and their prey is usually small snakes.

The average snake nabbed by a spider is 10 inches long. Some are only about 2.3 inches and in many cases are newly hatched.

There are hunting spiders and web-building spiders and they each have different strategies of attack.

For example, tarantulas are hunting spiders that don’t use webs to catch their dinner.

“Tarantulas are equipped with powerful upper jaws (chelicerae) and produce neurotoxins effectively targeting the snake nervous system,” Nyffeler says. “Often a tarantula tries to catch the snake by the head and will hold on in spite of all efforts of the snake to shake him off. After a few minutes, the spider’s poison may take effect, and the snake becomes quiet. Beginning at the head, the spider crushes the snake with its chelicerae and feeds upon its soft parts.”

Web-building spiders like black widows rely on a sticky tangle of threads to ensnare their food.

“The webs are very strong and tough, enabling the spiders to capture prey many times larger and heavier than themselves. When a small snake slides into such a web, it sticks to the vertical viscid threads,” Nyffeler says.

“The spider approaches the snake, throws sticky silk masses over it, and bites it one or more times. The neurotoxin thereby injected is a very potent, vertebrate-specific toxin (α-latrotoxin) that has proven to be highly lethal to small vertebrates. Subsequently, the spider pulls its victim off the ground, raising it between 10 and 120 cm [4-47 inches] above the floor, a process which may last several hours.”

While dying may not happen quickly, it may also take the spider some time to finish its meal.

“This usually takes several hours and sometimes several days for a spider to feed on a snake which can be explained by the fact that a snake is always a huge prey item for a spider,” Nyffeler says.

“Often a spider is not capable to ingest an entire snake. That is, a considerable portion of the snake cadaver may not be consumed by the spider. Usually, scavengers (ants, wasps, flies, mold) are finishing up the remains.”

Where Spiders Eat Snakes

Most of the reports of snake-eating spiders are in the United States (51%) and in Australia (29%). But snake-eating spiders can be found everywhere except Antarctica, the researchers found.

In the U.S., snake attacks by spiders have been recorded in 29 states and are expected in all parts of the country except Alaska. To a lesser extent, spider-eating snakes have been reported in the Neotropics (8%), Asia (6%), Africa (3%), Canada (1%), and Europe (less than 1%).

The only two reports in Europe were tiny blind snakes and the Canadian incidents were snakes trapped in spider webs.

“The reason why such incidents have been very rarely reported in Europe might be explained by the fact that the European colubrids and vipers (almost the only snakes occurring on this continent) are too big and too heavy (even as neonates) to be subdued by most European spiders,” Nyffeler says.

When he found snake reports and images, he often forwarded them to his coauthor, herpetologist Whit Gibbons, professor emeritus of ecology at the University of Georgia.

“My role in the research was the easy one, which was identifying the snakes that had become prey to spiders. Most of them were straightforward enough although I had to seek out colleagues in other countries for some of the exotics,” Gibbons tells Treehugger. “Martin did the heavy lifting in accumulating so many photographic records of spiders eating snakes, and identifying the spiders.”

Until he signed on to the projects, Gibbons had no clue there were so many spiders preying on snakes.

“I do not think any ecologist, including me, had any idea that snake-eating spiders were such a global phenomenon,” he says. “Spiders clearly play a significant role in ecological food webs.”

Nature at Work

This snake-eating spider research is important for several reasons, Nyffeler says.

He notes the ecologists study a concept called intraguild predation where natural enemies prey on each other and how this affects population and food web dynamics.

“Intraguild predation has become an important topic of modern ecology. My research is dealing with intraguild predation. On the one hand, we show that quite often snakes get killed by spiders,” he says. “On the other hand, we show that there are many snakes that include spiders in their diets. For instance, the diet of green snakes (Opheodrys) is made up of a large portion of spiders.”

Watching neurotoxins at work as spiders kill snakes can also be useful to pharmacologists and toxicologists who are working to gain insights into how these poisons affect the human nervous system.

But most importantly, probably, is just the observation of nature at work.

“Spiders and snakes are very interesting predators who play important roles in the balance of nature. To observe and report how these two predator groups fight with each other and kill each other is interesting documentation of natural history,” he says.

“The fact that often small spiders are capable of killing much larger snakes is very fascinating and knowing and understanding this enriches our knowledge of how nature works.”