How vampire bats drink your blood without you noticing

[00:00.41] As dawn settles on the Amazon, a bat opens wide and vomits blood into its companion's mouth.

[00:08.64] And it’s not the first time they’ve shared a meal.

[00:11.57] Vampire bats are the only mammals to subsist on blood alone.

[00:16.35] Their ancient ancestors might have eaten parasites and insects off larger animals till vampire bats began feeding directly from those larger animals themselves.

[00:27.77] There are three vampire bat species, all of which inhabit the warmer regions of Central and South America.

[00:34.94] Two of the three species— hairy-legged and white-winged vampire bats— more often prey on birds, quietly creeping up tree branches while they roost.

[00:46.89] But the most abundant vampire bat species is the aptly named common vampire bat.

[00:54.33] Following the nighttime routine of one such bat, we see that she sets out in pitch black, mapping her surroundings with ultrasonic sound waves.

[01:04.43] Common vampire bats are opportunistic hunters that have been observed to feed from snakes, sea lions, and pelicans, but they mostly take their meals from land mammals.

[01:16.91] And with the spread of agricultural areas, they increasingly target livestock.

[01:24.08] They've also been known to prey on humans, which carries dangers beyond just their bite.

[01:30.99] Bats are highly effective at dodging infections themselves, but they still carry pathogens.

[01:38.43] Vampire bats can transmit the rabies virus, making it all the more important that people living around them are protected, with measures like bat-proof sleeping shelters and vaccines.

[01:50.64] This night, the vampire bat homes in on a dozing pig.

[01:55.96] She cautiously swoops down and hops around to assess the situation's riskiness.

[02:02.86] With powerful, long forelimbs and thumbs, she can stand, jump, and even run on all fours.

[02:09.77] In fact, the vampire bats’ forelimb-powered bounding gait is wholly unique among animals.

[02:17.21] She uses specialized heat-sensing receptors to detect the warm blood running beneath the skin’s surface.

[02:25.97] And she finds a spot where she’s less likely to get caught, protecting herself from possible reprisal— and from starvation as she races the clock.

[02:35.80] She delicately pierces the pig’s skin with her curved, razor-sharp incisors.

[02:43.24] They have less protective enamel than most mammal teeth, and the friction between the upper incisors and lower canines helps keep them particularly pointy.

[02:54.93] In fact, vampire bats may have the animal kingdom’s sharpest incisors.

[03:00.24] Her saliva also contains a cocktail of proteins secreted from six glands in her neck.

[03:08.47] It keeps the blood flowing by preventing platelets from clumping and plasma proteins from turning solid, while also dilating the pig’s vessels and dissolving existing blood clots.

[03:23.08] She laps the flowing blood, the notch in her lower jaw shunting the liquid into two channels underneath her tongue.

[03:32.11] While blood is relatively nutrient poor, consisting mostly of water and some protein, her body and microbiome eke out what it offers. But she also has a fast metabolism and needs to replenish her energy stores quickly.

[03:48.85] A common vampire bat will perish without food for more than two nights.

[03:53.89] Ideally, she would stay stealth long enough to take in a little over a tablespoon of the pig’s blood.

[04:01.86] Then she’d be in good shape.

[04:04.25] But the pig starts suddenly, throwing her off.

[04:07.97] Dodging its trampling hooves, the vampire bat propels herself back into the night air.

[04:14.34] She tries to feed again, but each interruption puts her at greater risk.

[04:19.66] Thankfully, she doesn't live alone, and even though it's a considerable sacrifice, one of her companions throws her a lifeline— coughing up the hard-won results of her own high-stakes hunting heist and making it dinner for two.

[04:36.66] This isn’t uncommon. Vampire bats under two years old tend to miss a meal as much as once every three nights as they learn the ropes.

[04:51.80] So, their colonies rely on these rather extreme acts of cooperation to survive;

[04:57.91] without them, it’s thought their mortality rates would increase dramatically.

[05:05.88] Vampire bat colonies are networks of intimate grooming and food-sharing bonds— that go beyond blood, so to speak.

[05:08.80] A strong history of reciprocal food sharing and grooming can be even more important than relatedness when a vampire bat is deciding whether to donate a meal or respond to a contact call.

[05:22.34] So, thanks to her community, the bat survives, primed to regurgitate the favor in the future.