Spiders eating snakes, oh my! Here are the photographs to prove it

What's a spider with a discriminating palate to do when it gets tired of chowing down on its usual insect-heavy fare? A few nibbles of fresh snake might do the trick. Yes, some species of spider do indeed occasionally feast on snakes, according to a recent paper published in the American Journal of Arachnology. And that paper is chock-full of pictures to prove it.

Scientists had previously believed that spiders consumed live insects or other arthropods almost exclusively, but more recent research has shown their diets are more diverse. According to co-authors Martin Nyffeler (an arachnologist at the University of Basel) and J. Whitfield Gibbons (a herpetologist at the University of Georgia), various spider species have been found to feed on earthworms, velvet worms, bristle worms, slugs, snails, shrimp, crayfish, freshwater crabs, bats, mice, voles, rats, shrews, frogs, fish, newts, and salamanders, among other prey. There have also been multiple observed instances of spiders overpowering and feeding on snakes—usually baby or juvenile snakes.

Nyffeler and Gibbons decided to conduct the first synthesis of the various documented cases, poring through published reports, Google pictures, Google books, social media sites, scientific  journals, and relevant academic dissertations and theses. The team ultimately found 319 individual reports of spiders preying on snakes, most of them naturally occurring incidents, although about seven percent were laboratory feeding trials or staged field experiments. Nearly 80 percent of those reports included photos or videos documenting the gruesome acts for posterity.

Out of more than 49,000 known species of spider, the authors found 30 that had been observed to eat snakes in the wild, plus 11 other species shown to do so in captivity or staged field experiments. About half of all the documented cases involved widow spiders (exclusively females) of the Theridiid family, some of which appear to be "expert snake catchers," most notably the Australian feedback spider, the African button spider, Israeli and Iranian widow spiders, and four North American species. Tarantulas (Theraphosidae family) are the second most common spider family to feed on snakes, as these spiders hunt them in trees or on the ground. Large orb-weaving spiders (Araneidae and Nephilidae families) are the third most common to target snakes.

These three spider families accounted for 80 percent of all reported instances of feeding on snakes to date. As for their serpentine victims, the documented cases in the wild involved 86 species of snake from seven families, with another five species involved in captivity or staged incidents. These included brown snakes, crayfish snakes, garter snakes, green snakes, king snakes, ringneck snakes, racers, scarlet snakes, and rat snakes.

Different families of spiders kill their snake-y prey in different ways. For instance, black widows rely on their strong, tough webs to ensnare the snake in the web's vertical viscid threads. Then the widow will cover the snake in more sticky silk and bite it one or more times to release its neurotoxin venom. Once the snake has been immobilized, the widow raises its prey off the ground—a process that can take several hours—and kills and feeds at its leisure.

Tarantulas don't spin webs, but their bites also administer a powerful neurotoxin venom that can quickly immobilize a snake. A 1926 report described how a tarantula will grab a snake by the head and bite, holding on as the snake tries to shake it off. Once the venom kicks in, the tarantula will crush the snake and suck out all the yummy soft parts, leaving behind a "shapeless mass."

Orb-weaving spiders also catch the occasional small snake in their webs, and like the widow, they will wrap its prey in silk and administer a few venomous bites. The spider then "extracts the dissolved tissue from its victim by the process of extra-intestinal digestion," the authors wrote. (That is, the spider expels digestive enzymes from its intestinal tract, which break down the tissues into liquid for easy slurping.) Spiders typically only eat part of the snake, leaving the rest to scavengers like ants, wasps, and flies.

"While the effect of black widow venom on snake nervous systems is already well researched, this kind of knowledge is largely lacking for other groups of spiders," said Nyffeler. "A great deal more research is therefore needed to find out what components of venoms that specifically target vertebrate nervous systems are responsible for allowing spiders to paralyze and kill much larger snakes with a venomous bite."

Nyffeler and Gibbons also found that some black widow spiders can overpower snakes 10 to 30 times their own size. They cited one particularly extreme example documented by National Geographic in 1933, in which an 8-gram garter snake was trapped in the web of a cobweb spider weighing just 0.0225 grams. "Hence this snake was 355 times heavier than the spider," they wrote. Similarly, tarantulas (which can weigh as much as 50 grams) have been documented killing much larger and heavier pit vipers.

DOI: American Journal of Arachnology, 2021. 10.1636/JoA-S-20-050  (About DOIs).