Boas coordinate their bat hunts by forming 'curtains' of predation

Coordinated hunting. Orcas do it, wild dogs do it, even certain spiders do it. But when it comes to intentionally working together to catch prey, it's just so much more unnerving when you hear that snakes also do it.

These reptilian predators are not exactly known for being social creatures: the image of a solitary serpent is pretty typical. Yet some species do gather in groups for mating and hibernating, and some are even known to take care of their eggs. Now, a new study has revealed yet another unexpected social behaviour.

In March 2016, Vladimir Dinets of the University of Tennessee in Knoxville spent eight days observing the hunting habits of Cuban boas. These snakes live almost exclusively on their namesake island, and are one of the largest snake species in the West Indies. Their diet includes birds, rodents and lizards – but when the boas get a hankering for furry fliers, they crawl up the wall of a cave and catch bats.

The new study shows that Cuban boas (pictured) coordinate their hunts to increase their chances of success. Image: Vladimir Dinets

Coordinated hunting is pretty rare throughout the animal world, and has never been definitively observed in a snake species before. But in a sinkhole cave in Desembarco del Gramma National Park, Dinets saw snakes working together as they went after Jamaican fruit bats.

His is the first study to scientifically test the assumption of coordinated hunting in any reptile.

Now, we know what you might be thinking: you've seen snakes hunt in groups before. Perhaps you remember the swarming sea kraits from Planet Earth, or the even more infamous gauntlet of racers that terrorised an intrepid iguana in Planet Earth II:

However, experts argue that these snakes weren't truly working together – they were simply hunting the same prey in the same spot.

"To confirm that coordination does occur," Dinets explains, "one has to demonstrate that the predators take each other's position and/or actions into account, rather than simply gather in the same area."

The cave that Dinets staked out was host to nine Cuban boas, ranging one to two metres (3-6ft) long. Around dusk and dawn each day, one or more of the snakes would find a comfortable place on the ceiling to hang out just before the few hundred resident bats started their twice-daily flights in and out. The snakes didn't choose these hunting spots randomly – they kept each other in mind.

For as long as Dinets watched, every time multiple snakes came out to hunt at the same time, they would settle nearby each other. With two or three snakes in position, they formed an unsettling "curtain" of predation draping across the two-metre-wide (6ft) cavern. The more snakes turned up, the more fruitful the bat-hunting.

"They position themselves in a way that allows them to form a barrier across a cave passage," Dinets says. "This significantly improves the effectiveness of the hunt, apparently because they can most effectively block the prey's flight path and easily intercept passing bats."

At times when three snakes were out together, they each typically managed to grab a meal within just six or seven minutes. With only two snakes, it took ten minutes on average. And the three instances Dinets watched snakes hunting solo, one of them managed to catch a bat after an exhaustive 19 minutes, and the other two failed completely and gave up after almost half an hour of trying.

Dinets explains that one snake is easy for bats to avoid, but two or three snakes close together, blocking the passageway, leaves their flying food with fewer options. The serpents aren't exactly pack hunters, but the fact that this behaviour is so consistent, and that it significantly improves the snakes' hunting odds, suggests this teamwork is no accident.

"This possibility suggests that at least some snakes are not the 'solitary animals' they are commonly considered to be, and that they are capable of high behavioural complexity," he says.

But are Cuban boas the only snakes that do this? It's difficult to say, since most snakes' hunting tactics are not very well understood – after all, it takes a lot of waiting in the wild to see a snake grab a meal. On top of that, these island snakes are becoming more and more difficult to study as their numbers dwindle in the face of hunting by locals.

"I suspect that if their numbers in a cave fall, they can't hunt in groups anymore and might die out even if some of them don't get caught by hunters," Dinets worries. "A few of these caves are in national parks, but there's a lot of poaching everywhere."