Dark Banquet: Blood and the Curious Lives of Blood-Feeding Creatures Read online

  “I think Desmodus draculae might still be alive,” Arthur Greenhall told me during lunch one afternoon in Boston.

  “How do you figure that?” I said, after nearly choking on my sandwich.

  Greenhall explained that there were still regions in South America where very few people visited—the deep Amazon, and parts of Brazil’s Planalto Central, for example.

  “Besides,” he added, “draculae bones have been uncovered right alongside the remains of living species.”

  These facts, combined with the relatively recent discoveries of “living fossils” such as the coelacanth (a lobe-finned fish thought to be extinct for sixty million years) apparently gave the old vampire meister at least some hope that Desmodus draculae might still haunt the South American wilderness.*31

  “If only,” I replied. If only.

  I have not seen anything pulled down so quick since I was on the Pampas and had a mare that I was fond of go to grass all in a night. One of those big bats they call vampires had got at her in the night, and, what with his gorge and the vein left open, there wasn’t enough blood in her to let her stand up.

  —Bram Stoker

  3.

  SNAPPLE, ANYONE?

  It was still dark when we arrived at the slaughterhouse, but there were already several cars parked outside the nondescript, single-floor structure. We stood in the parking lot, finishing hot drinks—and not saying much—until the loud clank of a metal gate caused me to jump slightly.

  “You need more caffeine,” my companion said, sipping her decidedly low-test tea-water thing.

  I responded by pouring the remainder of my cup onto the gravel.

  As we approached the door, the aroma of my coffee gave way to the acrid tang of disinfectant and something else, something metallic, coppery.

  There were new sounds coming from within the building, shouts and a deep organic vibrato.

  At the abattoir, the workday was about to begin and we entered without knocking.

  My companion that morning was Cornell undergrad Kim Brockmann, whom I’d met several months earlier when she began showing up at our weekly Zoology Journal Club. After one such meeting I had inquired if anyone might be interested in volunteering to help me maintain some vampire bats that I hoped to bring back from Trinidad. Kim’s hand shot up without hesitation. Now, bundled up against the predawn chill, she was clutching six large plastic bottles and a spaghetti strainer, and I wondered if this is what she’d had in mind.

  In Trinidad, obtaining blood on a daily basis hadn’t been much of a problem, basically because Farouk Muradali, and more recently, his right-hand man, Keith Joseph, had been maintaining colonies of the common and white-winged vampires on and off for twenty-five years. During my first visit to Farouk’s lab at the National Animal Disease Center, I was actually rather bowled over at their success in keeping the white-winged vampire, Diaemus youngi, alive in captivity. Several references I’d previously read (including one coauthored by my friend Arthur Greenhall) stated that these bats could not be kept in captivity for any length of time.

  “Yes, we know all about those references,” Farouk said with a dismissive wave of his hand. “They’re one of the reasons why so little is known about Diaemus.”

  I bent over to examine a cluster of shapes that were gathered in the upper far corner of a spacious rectangular cage. All of the bats were asleep, except one, and he was watching me—mouth slightly open, sharp triangular teeth—strikingly white. Desmodus rotundus had black, beady eyes and an unmistakable air of intelligence. It was a look that Kim and I would become extremely familiar with over the next three years, one that always gave me the impression that the bats were waiting for me to make a mistake—the kind that would result in either their escape from captivity or the infliction of a savagely deep bite.

  Farouk nodded toward the cage and continued. “Desmodus is not a picky eater. If you capture one tonight and put out cow blood for it tomorrow night—it will drink until it’s full.”

  I nodded, recalling that these vampires had been given the species name rotundus because of their round-bellied appearance. Unfortunately, the naturalist Geoffroy never realized when he named them that their rotund abdomens were due to a gastrointestinal tract bloated with blood. Had he dissected a specimen he would have certainly noticed (as did Darwin’s friend and supporter Thomas H. Huxley) that the common vampire’s esophagus didn’t empty directly into the stomach, a feature that typifies all mammals. Instead, the lower end of the esophagus ended in an inverted T, one serif leading to the stomach, the other leading to the intestine. Furthermore, the stomach wasn’t J-shaped (as is seen in most mammals). It was tubular, a blind-ended U that was nearly two-thirds as long as the ropelike intestine that it closely resembled.

  Not surprisingly, researchers who sought to determine the route of ingested blood in vampire bats found that the going was weird indeed. In an experiment using barium-laced cow blood, an X-ray machine, and five (presumably grumpy) common vampire bats, G. Clay Mitchell and James Tigner determined that freshly ingested blood moved from the vampire’s mouth to the esophagus and then into the intestines before passing into the stomach.

  We know now that these variations in digestive anatomy and physiology (like other anatomical and behavioral adaptations) are related to the vampire bat’s unique lifestyle. In all other mammals, a primary function of the stomach is bulk storage of food—with some breakdown of that food (digestion). There is little transfer of nutrients or other material from the lumen of the stomach to the circulatory system (which then distributes it to the body).*32 This last, and generally overlooked digestive system function (absorption), is usually carried out by the small and large intestines and the network of blood vessels that supply and drain them. In vampire bats a key role of the stomach appears to be the rapid absorption of water (which makes up approximately 80 percent of the ingested blood volume). This excess water is carried to the kidneys (via the circulatory system once again) where much of it is converted into urine (i.e., water plus dissolved nitrogenous waste products). As mentioned earlier, since blood contains a negligible amount of fat, a substance in which energy is typically stored for later use, vampire bats are required to drink about half their body weight in blood each night.†33 This sudden weight gain is an extremely dangerous proposition for an animal that might be required to take flight at a moment’s notice. Because of this, an important adaptation for blood-feeding bats is their ability to shed weight as quickly as possible, and their digestive and excretory systems reflect this emphasis. Researchers who have observed common vampire bat feeding sessions know that the bats begin urinating well before they’ve finished feeding. Along with modifications to the typical mammalian stomach and intestines, evolution has cranked up the vampire bats’ excretory system, enhancing its ability to deal with its owners’ rather unique dietary requirements.

  Vampire bats get most of their nutrition from protein (in this case, hemoglobin and blood plasma proteins like albumin, fibrinogen, and globulin). These proteins are composed of smaller subunits called amino acids. In mammals, a problem arises when these nitrogen-bearing amino acids are broken down during digestion, releasing the toxic compound ammonia. Most mammalian excretory systems deal with ammonia by having the liver quickly convert it into a less toxic substance—urea. Urea is not only safer to have circulating around the body than ammonia but can also be more easily excreted by the body as urine (which is basically urea diluted with water extracted by the kidneys from circulating blood plasma).

  As a vampire bat begins to feed, the kidneys immediately begin producing an extremely dilute form of urine in order to shed excess weight (approximately 25 percent of the blood volume consumed is excreted as urine within the first hour after feeding). Soon, though, the excretory system shifts into a very different gear. The urine produced becomes more and more concentrated as the kidneys work frantically to eliminate the rapidly accumulating urea without causing dehydration in the bat.

  Because of t
he vampire bat’s need to excrete massive amounts of urea, water loss is a real and constant problem. Dehydration may have been one of the key factors that limited vampire bat ranges to regions that had a high relative humidity and may be one more reason why prehistoric vampire bats disappeared in North America. In a similar vein (sorry, I had to get that out of my system), vampire bats are restricted to relatively short-duration flights each night.*34 Presumably, this limitation is due to the evaporative water loss that typifies bat flight. So, although many bat species are known to migrate or undertake lengthy nocturnal flights, a sanguivorous diet appears to have selected against these behaviors in vampire bats.

  In 1969, Cornell University vampire bat expert William Wimsatt and his coauthor William McFarland put things in perspective: “In a very real sense the vampire bat can be considered to inhabit a desert in the midst of the tropics. But the desert is delimited not by environmental aridity, but rather by the nutrition and behavior of the vampire.”

  In both the vampire bats’ digestive and excretory systems, there have been evolutionary trade-offs related to blood feeding, as speed of food processing has been increased at the expense of nutrient storage. This type of trade-off is a hallmark of biology. Some organisms adapt to the changing environments in which they exist (e.g., vampire bats are able to feed on blood in a humid environment but can’t migrate or fly for extended periods). More often, though, organisms are unable to adapt—like many of the browsing mammals that died off as North American forests transitioned into grasslands. Although it’s certainly more fun to think about the big, sexy mass extinction events (like the one that occurred around sixty-five million years ago), the vast majority of species that have ever lived on this planet apparently disappeared rather gradually. Most extinctions, it seems, were accompanied by a whimper, not a roar.

  Farouk and I moved past the Desmodus cage to a smaller unit and peered in. Like their “common” cousins, all of the white-winged vampires were asleep except for one—but that was where the similarities ended. Where Desmodus has sharp, hard features (I’ve always maintained that they looked the part of vampires), Diaemus reminds me of a stuffed-animal version of a vampire bat. Their face is much softer—the sharp angles seem smoothed out and the eyes are huge and gentle looking. Their demeanor reflects these anatomical differences. In three years of handling Diaemus in captivity, they never attempted to bite me. Not once.

  Farouk shook his finger at me and then continued his lesson. “Now, if you leave out the same tray of cow blood for newly captured Diaemus, you’ll have dead bats in two nights.”

  I soon learned that Farouk’s “secret” for success was that each night he hand fed his newly captured white-winged vampires using a five-cubic-centimeter syringe full of cow blood. If the bats refused to eat, he didn’t force the issue but instead provided them with the opportunity to feed on a live chicken. Over the course of several weeks, even the most finicky of his “babies” got the message and soon enough he had them feeding on cow blood that he’d poured into an ice-cube tray. He supplemented his captive bats’ diet once a week (and probably on holidays) with feeding sessions on live chickens. These usually consisted of four hungry vampire bats to one soon-to-be-anemic chicken.

  Now it was all starting to make sense—why 99 percent of everything that had ever been written about vampire bats dealt solely with the common vampire bat, and why even bat experts had told me that all three vampires would act similarly. Desmodus rotundus had been maintained successfully in captivity for nearly sixty years—with some individual specimens surviving for as long as twenty years. Additionally, these bats were numerous across their widespread range and therefore relatively easy to obtain (hence the name “common,” I guess). They were also cheap to feed—as long as you had a ready supply of cow blood on hand. Plus, they were interesting as hell, with a slew of unique behavioral, anatomical, and physiological features.

  The other blood-feeding bats, Diphylla ecaudata, the hairy-legged vampire (which didn’t live in Trinidad), and its white-winged relative, Diaemus youngi, were far more rare (relatively speaking) within their limited ranges. They were much more difficult to locate and capture than Desmodus, and reports on the difficulty maintaining them in captivity only served to compound the problem.

  As a result, most researchers (with a few notable Mexican and South American exceptions) simply avoided working on two of the three vampire bat species. Hence, there were relatively few studies on these bats—especially on topics like comparative anatomy or behavior. Thanks to Farouk Muradali, though, who had graciously decided to let me in on his secret for maintaining Diaemus in captivity, the door would soon be wide open for the comparative work I’d proposed to undertake.

  Hand feed them until they start guzzling cow blood. How simple, I thought, until Farouk allowed me to do just that with one of the bats his crew had captured the night before. With no hesitation, I showed off years of animal handling experience by mishandling the syringe and squirting the poor creature with an eyeful of cow blood.

  “Must be the gloves,” I said.

  Farouk shot me a sideways glance, then smiled. “Yes, that must be it,” he said.

  Luckily for the bats, I got better.

  “Slaughterhouse Bob” reminded me of Popeye with an extremely selective case of Tourette’s syndrome. He was generally a friendly sort of fellow and he seemed genuinely amused that a couple of Cornell types showed up each week at 5 a.m. looking for cow blood. At the first sight of a health inspector, though, Bob’s conversation would undergo a seamless transition into a machine-gun barrage of obscenity that would have made the most hardened dockworker blush like a ten-year-old girl. It was an uncomfortable moment for the health inspector as well since the cursing was clearly directed at him. Additionally, while Bob was ranting he was also wielding a nasty device known in the slaughterhouse trade as a captive bolt stunner. This was an instrument that looked like a cross between a power drill and Dirty Harry’s .44 Magnum.*35

  Typically, Kim and I would stand back as Bob herded a single captive cow into the “stunning box,” a heavy-duty, steel-railed enclosure, designed to keep the doomed animal from doing anything more than just standing there. This process generally began right after the health inspector realized that there was somewhere else he needed to be. Stepping up onto the bottom rail of the box, Bob placed the business end of the captive bolt stunner against the cow’s skull, at the center of an imaginary X formed by the animal’s eyes and the base of its horns. Bob never appeared to rush and he never “chased the cow’s head,” taking his time for one clean shot.

  The concussive impact of the bolt stunner discharging sounded like a small-caliber pistol firing in an enclosed room (which in some sense is exactly what was happening). The results were as instantaneous as they were stereotypical. The animal collapsed, its brain penetrated by the steel bolt, which had already retracted back into the instrument.

  Bob bent down, checking for eye reflexes by touching the cow’s cornea. Anything resembling a blink would have meant that the creature hadn’t been properly stunned—although in three years of visits to the slaughterhouse we had never seen this happen.*36 Having been assured that the enormous bovid wasn’t about to right itself, Bob climbed agilely into the stunning box and disappeared behind the cow’s hindquarters.

  “This here’s the most dangerous part of my job,” came a muffled voice from somewhere just south of rump roast. “These cows still got nerves.”

  “That’s for sure,” I said, finally getting to use the anatomical knowledge I’d accumulated over a long collegiate career.

  “One stray kick can break a man’s back.”

  I pondered that image for a moment. “And that would suck,” I added thoughtfully.

  My colleague Kim (an aspiring anatomist herself) nodded in agreement. “Definitely.”

  In any event, I always got a bit antsy when Bob jumped in with a brain-bonked cow, and similarly, I always felt relief when Elsie rose from the floor, hind li
mbs first, cranking toward the ceiling under the power of a motorized block-and-tackle set.

  Less than a minute later, the insensate animal had been hung so that its head was suspended above a large plastic barrel. Then, with one expert slice of his knife, Bob would sever one of the cow’s jugular veins, stepping out of the way just in time to avoid the powerful torrent of blood that splashed into the blue container.

  Once the cow had been fully exsanguinated (and just about the time that Bob started reaching for the “carcass-splitting saw”), Kim and I slid the sloshing barrel of hot blood to the opposite side of the room. Clad in fishing waders and rain gear, our hands were gloved in rubber for reasons that Mr. Playtex couldn’t have imagined in his wildest nightmares. Even Bob shook his head in disgust—then he fired up the “Ronko Carcass Master 5000” and began the noisy process of carving Elsie into easy-to-carry pieces.

  Standing over the barrel, Kim and I took turns using a metal spaghetti strainer to agitate the blood. By doing so we were actually speeding up the natural clotting process—which had been chemically triggered as soon as the blood left the confines of the severed vein. Although unable to stem the flow of blood from a traumatic wound to a major blood vessel, the hemostatic (clotting) mechanism we were currently stimulating did an extremely efficient job of preventing excess blood loss after minor injuries. For example, a divot-shaped wound of the size inflicted by vampire bats (approximately three millimeters in diameter) would be expected to stop bleeding within one or two minutes. This is not the case, however, in instances in which the wound is created by one of nature’s blood-feeding specialists (e.g., leeches and vampire bats). Evolution has provided these creatures with a number of ingredients in their saliva that can interrupt the process of blood clotting for up to several hours. The end result is that the blood feeder is able to drink its fill, having temporarily halted the very same clotting process Kim and I were currently accelerating with our colander.