In the battle for creepiest crawly, some might argue that spiders and snakes are racing neck-and-neck. Both established hunters, they’re a staple for Halloween props and spooky sets, but both fulfill important roles within the ecosystem as predator and prey. Given their relative sizes, you might think most spider vs snake encounters end in favor of the snake, but a recent study has established that this is often not the case. Using their venom and strong webs, spiders across the globe can kill and eat snakes far bigger than themselves, something that took scientists by surprise.
Published in the American Journal of Arachnology, researchers carried out a meta-analysis based on literature from across the globe as well as social media surveys and uncovered 319 reports of spiders predating on snakes. The locations of the reports revealed that snake-hunting spiders exist on every continent except Antarctica, demonstrating that the unusual prey item is monopolized across a wide range despite spiders mostly feeding on insects. That said, the majority of reports (constituting about 80 percent of them) came from the US and, perhaps unsurprisingly, Australia.
In Europe, it’s a very different story. Countries in the region were home to just 1 percent of the reported spider-on-snake predation events and were limited to a group of diddy, non-venomous snakes from the family Typhlopidae.
Not all snakes were so small, however, with the largest among the reports being 1 meter (3.3 feet) long. The average length of snake from the meta-analysis was actually 26 centimeters (10 inches), with the smallest being just 6 centimeters (2.4 inches) long. The spiders were often still a lot smaller, with some taking down snakes that were 10 to 30 times their size.
Many of the captured snakes were far from defenseless, with around a third packing their own venom. Despite this, spiders in the US and South America were still found to be feeding on coral snakes and rattlesnakes, and in Australia, even brown snakes – some of the most venomous snakes in the world – were falling victim to redback spiders.
Black widow spiders were among the most successful at snake killing, being the perpetrators in around half of the cases uncovered in the meta-analysis. Hailing from the family Theridiidae, they’re able to successfully take out a number of animals including reptiles, amphibians, small mammals, and birds thanks to a toxin in their potent venom that has adapted to specifically target vertebrates. A similarly targeted toxin has been found to be part of the male Sydney funnel-web’s deadly venom, which is even dangerous to humans.
All in all, snakes were found to be prey for spiders from 11 different families, which in itself, the researchers on the study say was news. "That so many different groups of spiders sometimes eat snakes is a completely novel finding," said Dr Martin Nyffeler, arachnologist at the University of Basel, in a statement.
"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,” Nyffeler continued. “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.”