Sucking blood isn’t an easy life, even for vampires

Real vampires go well beyond bats to insects and even birds


blood mosquitoThe blood-sucking lifestyle of a mosquito is a hard one for many reasons, including getting smacked to death by a victim.

Jennifer Zaspel can’t explain why she stuck her thumb in the vial with the moth. It was just some after-dark, out-in-the-woods zing of curiosity.

She had been catching moths in the Russian Far East. On this July night, she had just eased a Calyptra into a plastic collecting vial. Its brownish forewings looked like a dried leaf. Of the 17 or so largely tropical Calyptra species, eight were known vampires. Males tend to dine on fruit. But on occasion they will drive their hardened, fruit-piercing mouthparts into mammals and sip some fresh blood. They feed off animals such as cattle, tapirs and elephants — even humans.

Zaspel, however, thought she was outside the territory where she might find a vampire species. She had caught C. thalictri. This species ranges from Switzerland and France eastward into Japan. And it’s widely known as a strict fruitarian. (Fruitarian means something only eats fruit.)

moth fingers
The tubelike mouthpart of a Calyptra thalictri moth extracts blood from a researcher. This moth was long thought to eat only fruit. And it is better adapted to pierce a plum than a thumb.
J. Zaspel

Before capping the vial containing this moth, “I just for no good reason stuck my thumb in there to see what it would do,” Zaspel recalls. To her great surprise, “It pierced my thumb and started feeding on me.”

So make that eight-plus Calyptra vampires.

Zaspel is an entomologist now at the Milwaukee Public Museum in Wisconsin. And she still is puzzling over the genetics of the moths at the two Russian field sites she visited in 2006. Males there will bite a researcher’s thumb if offered. But genetic testing so far shows the moths are part of a vast, otherwise mild-mannered species.

Which is just as well. As vampires go, these moths are not stealth biters. “I would compare it to a bee sting,” Zaspel says. For the sake of moth science, one of Zaspel’s colleagues voluntarily tried, despite the pain, to see how long a moth would keep feeding if no one brushed it away. The bite lasted 20 minutes!

Such bites definitely will get noticed. For these moths and other real-life vampires, being smacked to a smear is a bigger danger than getting staked through the heart.

Nabbing the occasional red lunch, or managing to survive on nothing but blood, is far more difficult than it looks in the movies. Relatively few animals manage this lifestyle. And all are indeed remarkable. Vampires include some insects and other arthropods, a few mollusks, some fishes and birds on occasion. Oh, and of course, there are three types of bats.

When dining on blood, there are pressures to gorge as much as possible at each meal. Such heroic volumes, however, can be outright toxic. At the same time, a blood meal is not nutritionally well-rounded. Some key nutrients are missing. Surviving this way takes guts as well as other specialized traits.

Modern tools of genetics and molecular biology are revealing what hidden specializations are needed for blood feeding. Science also is helping to make sense of the lifestyles that go to different extremes — even mouth-to-mouth blood donation.

Many of these biological adaptations would never fit among the showy strengths of the immortals of Twilight or True Blood. But the abilities could certainly count as superpowers.

Big dinner

To grasp the risks true vampires take, imagine an animal 35 million times your weight. Now bite it hard enough to make it bleed.

And risk making it mad.

vampire snail
Colubraria muricata snails are experts at sucking blood from fish. Found from South Africa to French Polynesia, the snail creeps toward a sleeping fish. Then it extends a long feeding tube (shown). The fish’s blood pressure probably pumps the meal to this parasite. The snail secretes a complex cocktail that may include a pain killer to keep the donor passive as this vampire downs its blood meal, says Marco Oliverio of Sapienza University in Rome, Italy.

“You can easily get killed by the host,” observes Pedro L. Oliveira. This insect molecular physiologist works at the Federal University of Rio de Janeiro in Brazil. The 35 million multiplier describes a 2-milligram (0.00007-ounce) female mosquito attacking a 70-kilogram (150-pound) human. These measurements came from an article Oliveira coauthored on nutritional overload in bloodsuckers. It appeared in the August issue of Trends in Parasitology.

Moreover, finding that giant blood source isn’t easy. “If you go into a forest, you have hundreds of meters separating one vertebrate host from another,” he notes. “Hundreds of meters would be several kilometers [a mile or two] for us.” Then the tiny vampire has to find a capillary — a tiny blood vessel — for biting that is just a few millimeters (about one-tenth of an inch) from the surface of the host’s skin. On a human victim, Oliveira estimates, only about 10 percent of the skin acreage will do.

With so many difficulties and dangers, “most of these guys try to minimize the number of visits,” Oliveira says. They drink fast, and they drink big. A young kissing bug, with its deceptively friendly nickname, can spread the debilitating and possibly fatal Chagas disease. That bug needs only minutes to down about 10 times its weight in blood.

To relate this to human physiology — forget it. There are people who intentionally drink blood (which is another story). But what they down is small in terms of what a real vampire would take away. It would be equivalent to the amount of swallowed blood from a long nosebleed, which can give a human diarrhea, notes Tomas Ganz. He’s a physician at the David Geffen School of Medicine at the University of California, Los Angeles. Fresh blood is difficult for the human gut to process. Plus, too little of the water in blood gets extracted and routed to the kidneys.

With such big blood meals, ingredients that would be harmless or healthful in small amounts now can prove toxic, Oliveira says.

Remove the water in blood. What’s left is almost 90 percent pure protein. Oliveira got an inkling of something perilous in that protein when his lab was exploring the genetics of one of the Americas’ kissing bugs.

This Rhodnius prolixus (ROD-nee-us Pro-LIX-us) has a rounded rear and body that narrows to a skinny little head. The bug lurks in crevices indoors or out. At night both males and females search for humans, their pets or other vertebrates pulsing with a good blood dinner. To be successful, this bug has evolved vampire superstealth. A kissing bug can bite a sleeper without waking that person. The bites of mosquitoes and ticks deliver pathogens in saliva. But a kissing bug delivers the Chagas disease parasite through its excrement. The bug leaves that gift on its host.

bug guts
Inside the gut of the Rhodnius prolixus kissing bug are enzymes that keep the tyrosine in its meals from crystallizing — and puncturing tissues. Arrows show white gut crystals that form when the enzymes are blocked.
M. Sterkel et al/Current Biology 2016

Researchers in 2014 detected many amino acids in that huge drink. The bugs had a massive array of special enzymes available to break down only one of them — tyrosine (TY-roh-seen) — as it washed into the kissing bug gut. Finding those tyrosine-busting enzymes in that gut is “kind of strange,” Oliveira says. In mammals, the liver and kidneys are the only organs with enzymes to break down tyrosine. Then again, most mammals don’t flood their guts with an overwhelming river of protein.

In the lab, researchers messed with the kissing bug to sabotage its breakdown of tyrosine. They either disabled genes or chemically blocked the enzymes. When changed in this way, the bugs died after dining. Oliveira and colleagues reported this last year in Current Biology.

Some of the dead bugs had crystals of tyrosine piercing right through the gut lining. This allowed their gut contents to leak into their body cavity. This discovery, the researchers now propose, might someday give molecular biologists their own drug to serve as a vampire-killing stake.

Blood feeding in insects and other arthropods has evolved multiple separate times (some say 21). But often the vampires have solved the challenge to safely dining on blood in different ways. The challenge of detoxifying tyrosine, however, might be a problem that a lot of critters have solved in unusually similar ways, Oliveira says. That similarity could help pest-fighters, he suspects. Why? Ruining the vampires’ protection against tyrosine might kill different menaces with the same kind of drug, he suspects.

Bad blood

Tyrosine is just one of the nutrients turned toxic by the massive size of blood binges. In the real world, a vampire’s ability to excrete wastes is much more important than some fictional power to hoist trucks.

Jonas Axelsson works at the Karolinska Institute in Stockholm, Sweden. He and his colleagues are studying kidney function in vampire bats. They’re comparing it to kidney health in bat species that live on fruit or nectar.

People typically eat some 50 to 120 grams (1.8 to 4.2 ounces) of protein a day. Eating like a vampire bat, though, would boost a 70-kilogram (150-pound) human’s intake to some 6 kilograms (13 pounds) of protein a day! That protein overdose means these bats have blood concentrations of waste produced by the protein’s breakdown, such as urea, that would be a short route to kidney failure in people.

Yet the vampire bats remain healthy. Their kidneys are only slightly bigger than other that of other bats, Axelsson says. Vampire bats just devote more of their kidneys’ space, he notes, to the long tubules that deal with reabsorbing useful substances from just-made urine.

Much of the protein in blood is hemoglobin. This iron-containing marvel molecule ferries oxygen around the body. This is what helps vertebrates live big and bold. Yet digesting so much hemoglobin in a hurry can free a massive, potentially poisonous dose of iron into the bloodstream.

lamprey teeth
The blood-sucking teeth of this sea lamprey look scary. Potentially more terrifying are the secretions that keep its victim’s blood from clotting.
T. Lawrence, GLFC

A healthy man makes his doctor happy with iron concentrations in blood of around 127 micrograms (0.000004 ounce) per 100 milliliters (3.4 fluid ounces). Yet concentrations up to 200 times higher don’t seem to harm fishes called lampreys during their larval years. At least, that’s what measurements from various lamprey species suggest. Their young pick up iron while burrowing in the bottom of waterways and eating anything that floats along. When sea lampreys (Petromyzon marinus) mature, they grow jawless toothy gapes. They attach themselves to the side of other fish species and suck their blood. Later, their iron levels in blood drop. Yet even then, they’re still 10 times higher than that of healthy people.

At first, a lamprey sticking to skin feels like “a moistened suction cup on your face,” says Margaret Docker. She’s a lamprey biologist in Canada at the University of Manitoba in Winnipeg. Half of the world’s 38 lamprey species suck blood. She has permitted one exploratory lamprey kiss on her cheekbone. It was from a blood-feeding silver lamprey (Ichthyomyzon unicuspis) found in North American lakes and streams.

Lampreys can generate a good grip. Some even mouth-suck their way up vertical waterfalls or dams. In the very unlikely event of a fish on the face, “the key is to dislodge it … before it starts to rasp in with the teeth on its tongue or oral disk — and before it secretes its anticoagulants,” Docker says. By that, she means blood thinners. A little prying with a fingernail is all it takes to break the suction.

Lampreys may have gone parasitic early in the history of vertebrates. So they have had a long time to evolve their vampiric method. A small fossil from some 360 million years ago, long before dinosaurs arose, shows an oral disk with 14 evenly spaced teeth. The creature already looked very capable of draining blood.

Not enough

Blood may have lethally too much of some things, but lethally too little of others. “Vampires don’t really have it that easy,” muses Rita Rio. She’s a microbial ecologist at West Virginia University in Morgantown.

Blood lacks B vitamins, Rio explains. These are essential nutrients for a wide range of basic bodily chores in animals. Among them: gene regulation, cell signaling and amino-acid breakdown. Animals can’t make their own supplies of these vitamins. Rio’s favorite vampire flies get around this problem with tiny live-in help.

“I have loved tsetse flies ever since I first learned about them,” she says. She’s speaking of sub-Saharan Africa’s Glossina flies. They have a “really cool biology,” she says. Their ability to spread a parasite that gives humans and some other vertebrates a potentially fatal sleeping sickness is more of a turn-off.

Tsetse flies look like robust house flies. They live very differently, however. Insect motherhood is typically low-involvement. Moms usually lay many little eggs and leave them to their luck. But a female tsetse fly has just one offspring at a time. A single egg hatches inside her. And as it grows, it draws sustenance from “milk” glands inside the mother fly. “You’ll see her getting chubbier and chubbier,” Rio says. A mother sometimes gives birth to a youngster that is bigger than she is. The youngster at that point has only its pupal stage to go before it reaches sexual maturity. Explains Rio, “It would be like me giving birth to a 12-year-old.”

Story continues below image.

tsetse fly
Tsetse flies (pregnant female, above) can survive on an all-blood diet thanks to bacteria that live in an organ ringing their midgut. Those Wigglesworthia bacteria churn out B vitamins, including B1, also known as thiamine. Both the fly and its resident bacteria need this vitamin.

As the mom fly gives her tween a pampered start in life, she also passes along an infection the youngster will need to reproduce on its nutritionally sketchy, all-blood diet. Each larva emerges with its own rod-shaped bacteria called Wigglesworthia. These bacteria flourish inside a special organ inside. There, the microbes churn out B vitamins. The tsetse-fly version of this organ is called a bacteriome. It “looks like a little doughnut around the digestive tract,” Rio says.

Low-fat bats

Another downside of blood is its low fat content, at least from the vampire bat point of view. Fat is a major energy source. So a small, low-fat meal won’t fuel the bat for very long. Yet extra cargo on a small flying mammal is limited to a mere 20 to 30 percent of the animal’s predinner weight. That’s one reason a common vampire bat (Desmodus rotundus) can’t go three days without drinking blood, says Gerald Wilkinson. He’s an evolutionary biologist at the University of Maryland in College Park. The danger of starving so fast may have encouraged the bat habit of blood regurgitation.

This razor-toothed mammal is one of three blood-feeding specialist bats. All are native to the warm latitudes of the Western Hemisphere. The first wild D. rotundus Wilkinson studied were on a ranch in Costa Rica. A bat “would often just fly up and land on the back of a horse,” he says. The bat has a fleshy little nose, “like a pig.” That nose can sense heat. And that’s useful in tracking down where warm blood flows close to the body’s surface.

vampire bat
The common vampire bat doesn’t suck blood; it licks it. Razor teeth nick flesh so the bat can lick up the gently welling blood.
Uwe Schmidt/Wikimedia Commons (CC BY-SA 4.0)

Actually, Wilkinson notes, getting that blood “was a very non-trivial thing” for the bats. They routinely spend half an hour selecting just the right spot on their prey. A bat may clip down horse hair, where needed. Then it will nick out a tiny divot of flesh. Afterward, the bat will lick the wound, often while urinating. And it will do this all without ever waking the horse.

Revisiting a wound on another night appears to be faster than prepping a new site. Wilkinson discovered one night that the bat he was watching on a horse had fed on the same horse, in a different pasture, the night before.

The bat’s saliva has impressive blood-thinning powers, Wilkinson reports. This keeps the blood from clotting. “I’ve been nipped a few times and the blood was hard to stop,” he says. “People who have been fed on will wake up and there’s a pool of blood. And the blood is often from after the bat left.”

Compared with bats of other species, the common vampire bat may even seem to have superpower moves. Instead of just flying, it easily runs across the ground.

When a hungry bat can’t find a meal for a night, the accomplished blood seeker may get a bit of blood from a luckier roost mate. They face each other, mouth to mouth. A well-fed bat sits motionless, he says, as “the other animal is licking.” It’s removing blood that a family member or friend was willing to share, having coughed that blood up into its mouth.

In his early experiments with captive bats, Wilkinson found animals willing to regurgitate on occasion for a hungry bat that’s not a relative. For decades, researchers have debated whether it’s fair to consider this blood donation as examples of natural altruism in vampire bats. This is when an animal does a service for another, at its own expense (meaning it gets nothing obvious in return).

Wilkinson’s former student Gerald Carter works in Germany at the Max Planck Institute for Ornithology in Konstanz. There, he has been studying this potential altruism. He put together unrelated bats from different zoos. He fed them blood collected from a slaughterhouse (not anybody’s favorite part of doing science). He then created short artificial food crises and recorded dozens of instances where one bat donated some blood to another.

Looking at all these examples of sharing, kinship didn’t matter, Carter and Wilkinson conclude. In captivity at least, a vampire will help a starving roost-mate who’s not a relative.

Carter even did a test of how a starving vampire reacts when its main go-to pal for emergency regurgitation “betrays” it by not helping. To simulate betrayal, Carter removed the potential helper from the others. That meant it couldn’t feed its starving roost-mate. On another night, he flipped their roles. The bat that had not helped its pal was now the hungry one in need of that pal’s regurgitated blood.

In general, he found, no hard feelings.

The partner bat who had been forced to deny blood often got fed, later, when it went hungry. The evidence so far looks as if vampires are hedging their bets in sharing blood. That’s what Carter, Wilkinson and Damien Farine of Max Planck proposed in the May Biology Letters. Bats that shared with many partners over the long run end up receiving more blood when they end up in trouble. In an uncertain world, this advantage might favor helping even non-kin. Vampirism may work as a force for generosity.

Way beyond bats

Baby vampire bats go for blood right away. They lick their mothers’ mouths for red regurgitation within minutes of birth. And there are many more vivid variations on vampirism.

There’s blood feeding in a vast dark and dangerous ocean. In some deep-sea ceratioid anglerfishes, males stay miniature. Later, upon finding a female, a male will meld his tissue with her giant body. They thereafter live off her blood system.

There’s also blood feeding by proxy. The jumping spider Evarcha culicivora hunts mosquitoes. It prefers those engorged with human blood. There’s even blood feeding as an impossible dream. Male mosquitoes sip flower nectar. But when scientists served the mosquitoes blood soaked cotton, they ate readily. Given nectar as an alternative, males still preferred the blood, even though it cut short their lives.

And there could be even more vampires out there that science hasn’t yet discovered. All it might take is someone sticking a thumb into a collecting vial.

Power Words

(for more about Power Words, click here)

adaptation     (in biology) A process by which an organism or species becomes better suited to its environment. When a community of organisms does this over time, scientists refer to the change as evolution.

altruism     When an individual does some helpful thing for another while expecting to get nothing in return.

amino acids     Simple molecules that occur naturally in plant and animal tissues and that are the basic building blocks of proteins.

arthropod     Any of numerous invertebrate animals of the phylum Arthropoda, including the insects, crustaceans, arachnids and myriapods, that are characterized by an exoskeleton made of a hard material called chitin and a segmented body to which jointed appendages are attached in pairs.

bacteria     (singular: bacterium) A type of single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).

bat     A type of winged mammal comprising more than 1,100 separate species — or one in every four known species of mammal.

binge     To do or consume something to excess — usually an unhealthy excess.

biology     The study of living things. The scientists who study them are known as biologists.

cavity      (in biology) An open region pocketlike structure surrounded by tissues.

Chagas disease     A potentially life-threatening disease that afflicts about 6 million people, mostly in Latin America. It’s caused by a protozoan parasite and is usually spread by contact with the feces of an insect called a “kissing bug.” Untreated, it can kill by destroying the heart muscle and its nervous system.

colleague     Someone who works with another; a co-worker or team member.

Costa Rica     A Central American nation with coastlines along both the Pacific Ocean and Caribbean Sea. This country of nearly 5 million people is sandwiched between Nicaragua to the north and Panama to its south. Almost one-fourth of its land consists of protected rainforests, which are home to such animals as spider monkeys and the quetzal birds.

crystal     (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals.

diarrhea     (adj. diarrheal) Loose, watery stool (feces) that can be a symptom of many types of microbial infections affecting the gut.

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.

digestive tract     The tissues and organs through which foods enter and move through the body. In people, these organs include the esophagus, stomach, intestines, rectum and anus. Foods are digested — broken down — and absorbed along the way. Any materials not used will exit as wastes (feces and urine).

entomology     The scientific study of insects. One who does this is an entomologist. A paleoentomologist studies ancient insects, mainly through their fossils.

enzymes     Molecules made by living things to speed up chemical reactions.

evolutionary biologist     Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).

evolve     (adj. evolving) To change gradually over generations, or a long period of time. In living organisms, the evolution usually involves random changes to genes that will then be passed along to an individual’s offspring. These can lead to new traits, such as altered coloration, new susceptibility to disease or protection from it, or different shaped features (such as legs, antennae, toes or internal organs). Nonliving things may also be described as evolving if they change over time. For instance, the miniaturization of computers is sometimes described as these devices evolving to smaller, more complex devices.

excrete     To remove waste products from the body, such as in the urine.

fat     A natural oily or greasy substance occurring in plants and in animal bodies, especially when deposited as a layer under the skin or around certain organs. Fat’s primary role is as an energy reserve.

fruitarian     An animal known to eat only fruit.

gape     A broad or wide opening, split or gap. For example, light shone through a gape between between the not fully closed drapes.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

gland     A cell, a group of cells or an organ that produces and discharges a substance (or “secretion”) for use elsewhere in the body or in a body cavity, or for elimination from the body.

hemoglobin     A molecule that binds to oxygen in the blood, carrying it around to tissues.

host      (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.

infection     A disease that can spread from one organism to another. It’s usually caused by some type of germ.

iron     A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

kidney     Each in a pair of organs in mammals that filters blood and produces urine.

kin     Family or relatives (sometimes even distant ones).

lamprey     An eel-like fish without hinging jaws, whose skeleton is made of bendy cartilage rather than hard bone. Like hagfish, they are considered to be “living fossils,” similar to the early relatives of vertebrates that lived hundreds of millions of years ago.

larva     (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)

latitude     The distance from the equator measured in degrees (up to 90).

liver     An organ of the body of animals with backbones that performs a number of important functions. It can store fat and sugar as energy, break down harmful substances for excretion by the body, and secrete bile, a greenish fluid released into the gut, where it helps digest fats and neutralize acids.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

mature     (adj.) Connoting an adult individual or full-grown and fully developed (non-juvenile) form of something. (verb) To develop toward — or into — a more complex and full-grown form of some individual, be it a plant, animal or microbe.

microbiology     The study of microorganisms, principally bacteria, fungi and viruses. Scientists who study microbes and the infections they can cause or ways that they can interact with their environment are known as microbiologists.

molecular biology     The branch of biology that deals with the structure and function of molecules essential to life. Scientists who work in this field are called molecular biologists.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

mollusks     Soft-bodied invertebrate animals that usually live in water and develop a hard protective shell. Examples include snails, shellfish (like clams and oysters), slugs, octopuses and squids.

native     Associated with a particular location; native plants and animals have been found in a particular location since recorded history began. These species also tend to have developed within a region, occurring there naturally (not because they were planted or moved there by people). Most are particularly well adapted to their environment.

nectar     A sugary fluid secreted by plants, especially by flowers. It encourages pollination by insects and other animals. It is collected by bees to make into honey.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

ornithology     The scientific study of birds. Experts who work in this field are known as ornithologists.

parasite     An organism that gets benefits from another species, called a host, but doesn’t provide that host any benefits. Classic examples of parasites include ticks, fleas and tapeworms.

pathogen     An organism that causes disease.

physiology     The branch of biology that deals with the everyday functions of living organisms and how their parts function. Scientists who work in this field are known as physiologists.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

proxy     An individual or thing designated to represent another; an alternative or stand-in.

pupal    (noun: pupa) Adjective for the life stage in insects following the larval (caterpillar) stage. It directly precedes adulthood.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.

regurgitate     To bring up something from the stomach that had been swallowed but not fully digested.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

roost     A place where winged animals temporarily rest or sleep. The term also refers to the act of resting on a branch or above-ground perch.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

secrete     (noun: secretion) The natural release of some liquid substance — such as hormones, an oil or saliva — often by an organ of the body.

social     (adj.) Relating to gatherings of people; a term for animals (or people) that prefer to exist in groups. (noun) A gathering of people, for instance those who belong to a club or other organization, for the purpose of enjoying each other’s company.

social network     Communities of people (or animals) that are interrelated owing to the way they relate to each other.

tapir     A large, nocturnal, plant-eating mammal that is shaped like a pig and closely related to horses and rhinos.

tick     A small eight-legged blood-sucking arthropod, related to spiders and mites. Although they look like bugs, these are not insects. They attach themselves to the skin of their host and feed on their blood. But in the process, they may spread any germs that could have been present in the blood of an earlier host.

tissue     Made of cells, any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

tract     A particular, well-defined area. It can be a patch of land, such as the area on which a house is located. Or it can be a bit of real estate in the body. For instance, important parts of an animal’s body will include its respiratory tract (lungs and airways), reproductive tract (gonads and hormone systems important to reproduction) and gastro-intestinal tract (the stomach and intestines — or organs responsible for moving food, digesting it, absorbing it and eliminating wastes).

tween     A child just approaching his or her teenage years. Tween is a term usually used for 11- to 12-years olds.

tyrosine      An amino acid (a building block of proteins). It plays a role in the production of some hormones and nerve-signaling compounds. It gets its name from the Greek word for cheese (tyros), from which it was first isolated in 1846.

urea     A nitrogen-rich chemical that the bodies of many animals produce after breaks down proteins, amino acids (the building blocks of proteins) or ammonia. People excrete excess nitrogen from the body — as urea — in urine. But many other mammals, amphibians and fish make urea as well. Synthetic urea is often a nitrogen source of plant fertilizers. In 1828, German chemist Friedrich Wöhler for the first time created urea in the laboratory. This discovery would lead to the widespread use of synthetic fertilizers in farming.

vertebrate     The group of animals with a brain, two eyes, and a stiff nerve cord or backbone running down the back. This group includes amphibians, reptiles, birds, mammals and most fish.

vitamin     Any of a group of chemicals that are essential for normal growth and nutrition and are required in small quantities in the diet because either they cannot be made by the body or the body cannot easily make them in sufficient amounts to support health.

waste     Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.


Journal: M. Munoz et al. Into the Wild: Parallel Transcriptomics of the Tsetse-Wigglesworthia Mutualism within Kenyan PopulationsGenome Biology and Evolution. September 1, 2017, doi: 10.1093/gbe/evx175.

Journal: G. Carter et al. Social bet-hedging in vampire batsBiology Letters. May 24, 2017. doi: 10.1098/rsbl.2017.0112.

Journal: M. Sterkel et al. The Dose Makes the Poison: Nutritional Overload Determines the Life Traits of Blood-Feeding ArthropodsTrends in Parasitology. Vol. 33, May 23, 2017, doi:10.1016/

Journal: R.V.M. Rio et al. Grandeur Alliances: symbiont metabolic integration and obligate arthropod hematophagyTrends in Parasitology. Vol. 32, September 2016, p. 739.  doi: 10.1016/

Journal: M. Sterkel et al. Tyrosine Detoxification Is an Essential Trait in the Life History of Blood-Feeding ArthropodsCurrent Biology. Vol. 26. July 28, 2016, doi: 10.1016/j.cub.2016.06.025.

Journal: M.F. Docker (ed.). Lampreys: Biology, Conservation and Control. Springer 2015.

Journal: M.V. Modica et al. The venomous cocktail of the vampire snail Colubraria reticulata (Mollusca, Gastropoda). BMC Genomics. Vol. 16, published June 9, 2015, 441. doi: 10.1186/s12864-015-1648-4

Journal: T. Plantan et al. Feeding preferences of the red-billed oxpecker, Buphagus erythrorhynchus: a parasitic mutualist? African Journal of Ecology.  Vol. 51, June 2013, p. 325. doi: 10.1111/aje.12042.

Journal: J.M. Zaspel et al. Another blood feeder? Experimental feeding of a fruit-piercing moth species on human blood in the Primorye Territory of Far Eastern Russia (Lepidoptera: Noctuidae: Calpinae). Journal of Insect Behavior. Vol. 20, September 2007, p. 437. doi: 10.1007/s10905-007-9090-3.


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