As Halloween draws near, Nilo Mason unveils the shadows of the animal kingdom and the macabre world of blood-sucking creatures that would impress even Count Dracula himself. From the notorious vampire bat (Desmodus rotundus), to the lesser-known “Cooper’s Nutmeg'' sea snail (Cancellaria cooperii), this article gives you plenty to think about this Halloween.
Starting off with the famed common vampire bat (Desmodus rotundus), these flying mammals feed from blood that pools in the open wound of their victim, by creating a new bite wound, or by opening a previous wound. The common vampire bat is one of three vampire bat species, with this one specialising in mammal blood (from cows, pigs, and horses) while the other two target birds. It is predicted that this sanguivory evolved from an insectivorous ancestor by eating ectoparasites, wound feeding, or a combination of the two eating styles.
Having evolved 28 independent times in evolution, you would think that Dracula’s technique would be easy to replicate, but vampire bats face a multitude of challenges when trying to feed: the victim defending itself, blood clotting, and the poor nutrient content of blood. A simple solution to the first problem, the bats prey on their mammalian victims while they sleep – rendering them unaware of the snack they’ve become. Also the bats saliva contains anticoagulants that prevent the blood from clotting or forming a scab, allowing the bat to lap up a continuous flow of their gruesome meal.
Finally, to combat the low nutrient content, bats consume 15-25mL of blood per meal; they finish a meal weighing 50% more than when they started! However, most of the content is water that the bats urinate out. So, believe it or not, despite the high volume consumed, blood is not a hearty meal for bats. It's more like trying to fill up on celery sticks – all protein and water, no fat, so these little guys are on a constant quest for seconds!
Vampire bat (Desmodus rotundus). Image Credit: Uwe Schmidt on Wikimedia Commons.
Next up is the sea lamprey (Petromyzon marinus), feeding on blood at a rate of 3-30% of its wet body weight; this thirsty creature is considered a parasite to the fish it feeds on. Similar to leeches, sea lampreys attach themselves to the flesh of their victim with their thorn-like teeth, rasping tongue, and “sucking disk”. Inflicting wounds up to 75mm in diameter, these water vampires pack a punch, even killing their hosts sometimes. Although not killing them directly, but by damaging the fish’s scales and mucus layer, the fish loses the only protective barrier it has from the water around it, leading to life-threatening infection or an unwanted influx of water into the body.
Alike to the aforementioned vampire bat, sea lampreys also utilise their saliva as an anticoagulant. However, this time, the unique substance Lamphredin, secreted from their buccal (cheek) glands, serves a multifaceted purpose. It prevents host blood from clotting, breaks down red blood cells, and aids in digesting host tissue – allowing for an all-you-can-eat buffet! But why did they pick the vampire lifestyle? Aside from the cool teeth, hematophagy (or blood-feeding) allows sea lampreys to reach their full adult form, increasing their total weight and length exponentially. Before they metamorphosize into their final form and head to the seas, they live buried in sediment upstream in rivers as humble filter feeders, finally undertaking a 4-10 month fast during and after their transformation. No wonder they need the continuous supply of blood straight after!
Sea lamprey (Petromyzon marinus). Image credit: T. Lawrence and Great Lakes Fishery Commission on Wikimedia Commons.
Native to the infamous Galapagos islands, the vampire ground finch (Geospiza septentrionalis) does something no other finch would dream of. Whenever resources are scarce in the dry season, this feathered ghoul supplements its diet with the blood of other birds, namely, Nazca and red-footed boobies (Sula granti and S. sula). Although their beak does not have fangs, it is the sharpest of all species of Darwin’s finch, perfect for piercing flesh and drinking the blood they need to stay hydrated.
Their home range includes two small islands (Darwin and Wolf), each less than a mile big, and separated from any larger islands by 100 miles of open ocean. With freshwater being scarce on these islands, and the distance to another being too far to fly for them, these cute little finches have resorted to using blood to get much needed freshwater. But how did they discover to do this? It is likely that this hematophagy began as picking parasites off of the larger bird – helping each other out, or mutualism – however this often caused lesions in the skin, leading to blood also being consumed directly. The vampire finches then just started going straight for the source!
Vampire finch (Geospiza septentrionalis). Image credit: Peter Wilton on Wikimedia Commons.
Finally, the last Dracula-wannabe on our list, the Cooper’s Nutmeg sea snail (Cancellaria cooperii). Reaching a size of 95mm, this sea snail is considered medium-large and, like the sea lamprey, is also considered a parasite. Living in the Eastern Pacific Ocean its home range spans from Monterey in California to Baja California in central Mexico, here it preys on unsuspecting Pacific electric rays up to even 210 metres deep at the ocean floor. However, unlike the others on this list, this snail has a more sinister and calculated feeding technique. Beginning the hunt by following a rays chemical trail for up to 75 feet, the stalker then uses its 4-inch proboscis (or snout) containing tiny teeth to probe into the flesh, gills, mouth, or anus of the ray, sucking blood up into its digestive system through the tube. Somewhat of a gruesome straw! It is also hypothesised that the snail emits a toxin which provides a local anaesthetic to the ray so they won’t even notice the vampire attached to their underside. Being so rare, little is known about this snail and why they feed on blood, but they are commonly found within the vicinity of or attached to electric rays, and may even prey on other benthic (bottom dweller) fish.
As far as vampires go, it is far from just fiction. These examples demonstrate the remarkable adaptability of nature and the extreme lengths creatures will go to survive in harsh conditions. However, unless you are a large hoofed mammal, blue-footed booby, fish, or electric ray, you have nothing to worry about. As we celebrate Halloween and all things scary, remember that monsters of the night are not necessarily werewolves and ghosts, but come in the form of little birds and beautiful sea snails, and they are all to be admired.