Forget pasty Transylvanians in black cloaks and eternal teenagers that sparkle in daylight. These are the real bloodsuckers of the animal kingdom.
Vampire finch (Geospiza difficilis septentrionalis)
This villain’s haunt is worthy of its own gothic novel. Isolated by 620 miles (1,000km) of ocean on all sides, Wolf Island looms eerily over the Pacific. It is the most remote outpost of the Galapagos – a barren land of razor-sharp lava formations, tangled mangroves and brutal heat. And it is ruled by vampires.
The tiny, ordinary-looking vampire finch is a close relative of its seed-eating neighbour, the sharp-beaked ground finch. But looks belie a grisly secret.
Although they still eat seeds and grubs, the birds have adapted to island life by turning their beaks to more violent use. To feed, they simply hop aboard a larger bird, such as a blue-footed booby, and peck at the tail feathers until they are sitting in a pool of blood. Then the vampires jam in their beaks and go to town. They are particularly fond of defenceless chicks cowering in their nests.
Perhaps the most sinister aspect of the whole ordeal is that the victims barely flinch as the finches rip their skin off. One theory is that the vampires used to pick ticks off the birds – they may have discreetly taken their services to the next level. Or perhaps resisting just isn’t worth the effort.
The finches’ blood-drinking habits have allowed them to thrive even in the driest months, becoming the most numerous birds on the island. At peak feeding times, finches can be seen lining up behind a victim, patiently waiting their turn to dine.
Assassin bugs (Reduviidae family)
In woodlands and rainforests across the globe, a cold-blooded killer stalks the night. The aptly-named assassin bug has it all – stealth, strategy, and a lethal weapon.
The 7,000 or so species vary widely in their diets – some target bees while others, confusingly, suck the blood of blood-sucking vampire bats – but all are equipped with their own sinister multi-tool, the rostrum.
While other predators go to the trouble of killing their prey, the assassin bug uses its rostrum to inject live victims with cocktail of enzymes and digest them from the inside out. As the target animal turns to soup, the assassin bug’s beaklike projection then doubles as a drinking straw for slurping up the soup – whether the victim is alive or dead.
Most assassin bugs feed on insects, which they ambush using a range of nasty tricks. The species Stenolemus bituberus hunts spiders on their own webs, luring them to their doom by gently plucking the delicate silk to mimic the vibrations of entangled prey. Then it leaps out of hiding.
But for sheer guile you can’t beat Salyavata variegata, which goes fishing for termites. First it finds some bait: it waits by the entrance to a nest, impales a worker, and sucks it dry. Then it thrusts the victim back inside. Invariably it emerges with another live termite to attack, which has clung to the body of its dead comrade – undone by a powerful instinct to pick up and remove termite corpses from the nest.
Another species, Acanthaspis petax, preys on ants. It puts its victims’ shrivelled corpses to particularly macabre use, gluing them to its shell as extra armour. Some have been seen with as many as 20 individuals piled up.
Unfortunately, humans haven’t escaped the assassin bugs’ attention. The ‘kissing bug’ has been drinking our blood for thousands of years. So-named because of their hideous habit of attaching themselves to peoples’ faces as they sleep, they even managed to annoy the world’s most famous biologist. Charles Darwin encountered them on his iconic voyage aboard the Beagle. He later wrote of the experience: “It is most disgusting to feel soft wingless insects, about an inch long, crawling over one's body.”
The bugs are the leading source of Chagas disease, caused by protozoans which live in their gut and contaminate the wound as they feed. It’s a silent killer, quietly ravaging a person’s heart for the rest of their life. Some believe it may have been responsible for Darwin’s death.
Vampire flying frog (Rhacophorus vampyrus)
The mist-swept forests of Southern Vietnam are some of the wettest places on Earth, permanently submerged in clouds which drench every surface in the canopy. It is ideal for spotting amphibians – but not obvious vampire territory.
Or so biologist Jodi Rowley thought when she visited in 2010. Before long her team had found a species of flying frog entirely new to science.
Back at the Australian Museum in Sydney, where Rowley works, she was having difficulty seeing the tadpoles’ tiny eyes. She popped one under the microscope to get a better look.
“It was to my great amazement that I saw these curved black fangs sticking out! I just assumed that they’d have the normal mouthparts for tadpoles which, you know, are quite boring beaky things,” Rowley told BBC Earth. Why would a tadpole need fangs?
The frogs live their entire lives in the treetops, where they use their webbed fingers and toes to glide among the trees.
Instead of risking predators by laying their eggs in streams or pools on the ground, females place the eggs above water-filled holes in the trees, whipping them up into a sticky foam with their back legs.
As the tadpoles hatch, they liquefy the foam and drop into the water below. But there is nothing for them to eat, so the mother returns to the hole and lays more eggs.
“They don’t suck blood or anything, they use the fangs to scoop the eggs up into their big mouths, and they suck them down whole.” Rowley explains.
Kenyan jumping spider (Evarcha culicivora)
It’s hard not to feel sorry for the Kenyan jumping spider. The arachnid, which stalks the walls of people’s homes on the shores of Lake Victoria, loves nothing more than a refreshing drink of human blood. But fate has been unkind: the spiders lack the specialised mouthparts needed to pierce people’s skin.
Instead they must get their fix indirectly, which they do by preying on blood-filled mosquitoes. They are the only animals known to choose their prey based on what it has eaten, and the spiders are extremely fussy.
Given the choice, they only eat female Anopheles gambiae mosquitoes, the main malaria vector in Africa. But picking out a single species from the swarms of insects in the region is no mean feat.
The spiders distinguish Anopheles mosquitoes by the 45 degree angle of their bodies as they rest, and they can distinguish a mosquito that is full of human blood from one that isn’t by smell alone. What Ximena Nelson from the University of Canterbury, New Zealand, wanted to know was: how do they tell the females – which drink human blood – from the males that don’t?
To find out, Nelson launched a bizarre experiment, which involved painstakingly constructing a series of mosquito monsters worthy of Frankenstein. She cut the heads, thoraxes and abdomens off males and females from two different species, and glued them back together in different combinations. Then she mounted their bodies in life-like postures, and presented them to the spiders.
It turns out what the spiders prize above all else are fluffy, luxuriant antennae; they went for the creations with female heads every time.
Tongue-eating louse (Cymothoa exigua)
In January 2015, the internet retched in unison when a Nottingham mother opened a tin of tuna to find a pair of beady eyes peering back at her. The instigator of #tunagate turned out to be a Cymothoa exigua. It is a louse with a life so implausibly creepy, you couldn’t make it up.
The parasite starts life as a male in search of a fish. Once it has found a suitable victim, it enters through the gills, crawls into the mouth, and undergoes a transformation.
It plunges its legs into the base of the fishes’ tongue and gorges itself on their blood, growing enormously and turning female at the same time. Its eyes shrink and its legs expand.
Eventually, the fish’s shrivelled tongue falls off, and the louse replaces it with its own body. From then on, the fish uses the parasite as a prosthetic tongue. The female mates with males living in the gills, giving birth to a brood of live male parasites that swim off to start the whole grisly process again.