Dark Banquet (30 page)

Could this happen? University of Calgary biomechanics expert Dr. John E. A. Bertram doesn't think so.

“In order to swim up a pee stream, the fish would have to swim faster than the stream flow. Additionally, to climb the stream, the candiru would have to lift itself out of the water against gravity. And while a small fish might be able to jump a surprising distance through the relatively low resistance air—a stream of urine would be another story.”

“Why's that?” I queried.

“Because the penis tip acts as a very efficient nozzle,” he said, “creating a stream of specific form, largely due to its high velocity of flow. Presumably, this keeps us from urinating on our feet. In any event, even if the candiru could power itself up the stream, it would have to stay completely within the urine and that would be difficult.”

“How come?” I asked.

“Because the narrow urine stream has boundaries with the relatively low-density air. If the fish wandered into this boundary, the low resistance flow of the air would destabilize it—essentially pulling the candiru out of the high-drag pee stream.”

I mentioned this explanation to Stephen Spotte, who agreed with Bertram. “I just don't see how it's possible,” he said. “The candiru would be trying to swim, and the lateral sweeps of its tail would be wider than the urine stream. So in addition to destabilizing its body, it wouldn't be able to generate the thrust it needed.”

“So was this Brazilian guy just making it up?”

“I don't think so,” Spotte said. “I mean he didn't even know what candirus were, so it's hard to believe that he invented the story. I still think he was, you know, pissing right at the surface—and then it would be possible.”

“How so?”

“If you've ever watched these things feeding in an aquarium, they shove themselves right under a fish gill—I mean it's a rapid, violent motion. It happens instantaneously—you can't even see it. So it's possible that this fish got up there so quickly that the guy didn't even have time to react. That part I believe.”

“How long do you think a candiru could survive inside a human urethra?” I asked.

“Catfish can live a long time in pretty dire circumstances,” Spotte replied, and I noticed that his voice had taken on an ominous tone.

“How long are we talking about?” I asked, a little fearfully. “A couple of minutes?”

“More like a couple of hours,” he said, “although this one was certainly dead by the time they pulled it out of the victim.”

I was almost afraid to ask the next question. “When was that?”

“They did the surgery three days after the guy came in. Besides the pain in his penis, I can't even imagine what it was like not being able to urinate for three days. Dr. Samad said that his abdomen was swollen like a soccer ball. He was a tough dude.”

So why would a candiru abandon its normal, gill-feeding lifestyle for a visit to the Telegraph Office? In his book, Stephen Spotte reviewed several current hypotheses.

In the “urine-loving hypothesis,” the candiru seeks to embed itself in a mammalian urethra with its ultimate destination being the urinary bladder.

“This whole idea of candirus being attracted to urine is problematic,” he told me. “For one, urine is not listed among the major food groups.” And in fact, no other vertebrates are known to feed solely or even predominantly on urine.

Then there was the oxygen—or lack of it actually. Oxygen is a requirement for every other vertebrate on the planet, and in a urine-filled bladder there wouldn't be any. Additionally, urine would be far saltier than the fresh water of the Amazon and the temperature would be significantly higher as well. All in all, it was a trip that sounded more suicidal (or accidental) the more I learned about it.

Interestingly, these apparent drawbacks didn't stop Carl Eigenmann, one of the top ichthyologists of his day, from proposing that “further study may demonstrate that some species of Candirús have become parasitic in the bladders of large fishes and aquatic mammals.”

Once again, Stephen Spotte was not convinced. “Paulo Petri and I did some experiments, both in the field in sort of a quasi-laboratory situation, and we got no response at all.”
^*148

Another hypothesis proposes that candirus become accidentally embedded in the human urinary tract owing to a behavior called rheotropism, which is defined as the movement of an organism in response to a current. The idea here is that the candiru mistakes the flow of human urine for that of a natural flow of water (like the current produced as water leaves the gills of a large host fish). In what has become known as the “wrong turn hypothesis,” after the candiru mistakenly enters the urethra, its backward-curved odontodes prevent it from turning around. The trapped creature continues forward until it dies from a lack of oxygen.

Yet another hypothesis posits that the candiru tracks its piscine prey by the chemical trail the larger fish leaves in its wake. If chemicals typically found in human urine (possibly ammonia, the protein albumin, and creatinine—a breakdown product of muscle physiology) also serve to stimulate the candiru's host-hunting behavior—this might explain the creature's attraction to the human urethra. Sweat has also been suggested as an attractant, although this doesn't explain why the candiru headed for the tip of FBC's penis.

“It could certainly be something in the urine,” Spotte told me. “It could also be the urine flow itself.”

I decided to try out my own hypothesis. “What about the possibility that the candiru are reacting to a disturbance in the water—at least initially. They think they're reacting to a large catfish, and by the time they get close enough, it's too late.”

“The problem with that is the fact that Paulo and I caught many of these fish in the middle of the night, in rapids—I mean you couldn't even stand up in this water. And yet we tethered a catfish out there and within thirty minutes the candirus found it. Now they weren't detecting movement because this catfish wasn't swimming.”

“So what do you think the candiru are detecting?” I asked.

“Nobody really knows, but my best guess would be that it's a combination of things. Catfish can taste and smell—they've got all these really well-defined sense organs, specialized for dealing with low-visibility environments. Probably, they sense something in the fishes' protective slime—which is sloughed off continuously, just like we drop old hairs. Candirus also have an array of pores around their heads, so it's also likely that they're detecting the electromagnetic charges generated by things like muscle contraction. In any event, it's an interesting problem and it just goes to show catfish are amazing creatures.”

“What about attacks on nonhuman mammals,” I asked, adding that I thought it strange not to have come across any in the literature.

“None,” Spotte replied. “We haven't got any evidence. But you're right. Why don't they attack dolphins and manatees and river otters—they're certainly releasing stuff into the water—and they've got some very large orifices.”

The scientist continued. “As far as human encounters with candirus, I just can't think of it as anything other than an accident. But how it arrives there—that's still a mystery.”

I asked Dr. Spotte a final question. “What do you think the odds are that someone submerged in a stream where candiru live, and deciding to take a pee, would get attacked by these creatures?”

Dr. Spotte replied without hesitation. “About the same as being struck by lightning while simultaneously being eaten by a shark.”

What was so thought provoking about all sorts of Galápagos finches to young Charles Darwin…was that they were behaving as best they could like a wide variety of much more specialized birds on the continents. He was still prepared to believe, if it turned out to make sense, that God Almighty had created all the creatures just as Darwin found them on his trip around the world. But his big brain had to wonder why the Creator in the case of the Galápagos Islands would have given every conceivable job for a small land bird to an often ill-adapted finch? What would have prevented the Creator, if he thought that the islands should have a woodpecker-type bird, from creating a real woodpecker? If he thought a vampire was a good idea, why didn't he give the job to a vampire bat instead of a finch, for heaven's sake? A vampire finch?

—Kurt Vonnegut

10.

A TOUGH WAY TO MAKE A LIVING

I
n addition to vampire bats, leeches, bed bugs, ticks, mites, and candirus, there are literally thousands of species that feed on blood. They range from intestinal nematodes called hookworms, that produce iron-deficiency anemia in their hosts,
^*149
to mosquitoes, one of the eleven families of fly-relatives (dipterans) with blood-feeding members. There are assassin bugs (which may have plagued Charles Darwin) and vampire moths (seven species in the Asian genus
Calyptra
). These insects use their sharpened mouthparts to pierce the skin of animals like water buffalo, elephants, tapirs, and even humans.

Then there's
Geospiza difficilis,
the pint-sized vampire wannabe that so impressed author Kurt Vonnegut. Although dramatic, “vampire finch” is not a terribly accurate name for this bird, which is also known as the sharp-beaked ground finch. Basically, the vampire tag is questionable, because unlike the other sanguivores mentioned thus far,
Geospiza difficilis
is not an obligate blood feeder.
^*150
The birds merit mention here, however, because they appear to be giving part-time vampirism a serious shot. In that regard, they occasionally supplement their normal diet of small seeds and nectar by eating eggs and by pecking at the wings, body, and tail regions of another Galápagos resident—the blue-footed booby
(Sula nebouxi).
Once
Geospiza difficilis
has inflicted a small wound with its beak, it begins sipping the booby's blood, hopping out of the way if the larger bird gets annoyed. The finches feed in this manner for several minutes, giving way to other individuals who line up, waiting their turn like customers at a deli counter.

Geospiza difficilis
is widely distributed throughout the Galápagos archipelago, but only two populations feed on blood. Researchers have noted differences in feeding behavior, size, and vocalizations in these birds—differences that could indicate that a new finch species is forming before their eyes. For my own part, it's just as interesting to imagine what might happen if
Geospiza difficilis
became a bit more adept at obtaining a blood meal, and a bit more dependent on finding one on a daily basis. What if conditions on the tiny islands of Darwin or Wolf changed, and the seeds and flowers these birds needed to survive were no longer available? Would the blood-sipping finches simply relocate to another island? Perhaps, but if they did, they'd certainly run into competition from the well-established finch species already living there. Maybe the vampire wannabes would die out or interbreed with non-blood-feeding members of their own species. Or maybe
Geospiza difficilis
would accumulate a few more beneficial mutations (to its digestive system perhaps), until it had evolved into a
real
vampire finch—a feathered version of
Desmodus rotundus.

Beyond the hypothetical, though, blood feeding makes absolute sense—and because it does, it should come as no shock that there are thousands of obligate sanguivores out there, as well as others that supplement their diets with blood.

But why does a blood-feeding lifestyle make sense? To address that issue, I'll start off by repeating the two questions I hear most often about vampires: (1) Why do creatures like ticks, vampire bats, and bed bugs even exist? and (2) What would it matter to the earth if all the blood-feeding creatures suddenly disappeared?

These are questions that I've been hearing pretty much since I began working on vampire bats in 1990, and while the first question is certainly valid, the second question illustrates a basic problem that most people have with science. That is, they don't think like scientists. Don't get me wrong, though. It's hard not to empathize with anyone who's been swarmed by black flies, suffered through malaria or Lyme disease, or experienced the twitching paranoia of a bed bug infestation. For most people, then, it's only natural to envision a world where these nasty critters didn't pester, sicken, and kill us with such incredible efficiency.

But vampires, whether they're bats, leeches, or bed bugs, don't exist to sicken or kill us. They exist because their ancestors evolved certain characteristics that allowed them access to a highly specific but worldwide resource, a resource that they could utilize as food.
^*151
That resource, blood, has been vital to the existence of every vertebrate that has ever swum, crawled, walked, run, or flown.
^†152

With the aid of a muscular pump, blood travels through a wildly complex system of interconnected tubes. Sanguivores have evolved ways to exploit the accessibility of these tubes and, just as important, the fact that they can be opened and tapped. Given the potential for running into creatures hauling around these tubular filling stations, it would be remarkable if sanguivory
hadn't
evolved in a diverse array of taxonomic groups. But here's the catch. No matter how different blood feeders are from each other (exemplified by leeches and bats), there appear to be a finite number of ways that a sanguivore can successfully gain access to a meal. For this reason, vampires as different as bats and leeches share separately evolved but similar adaptations for their highly specialized lifestyles—that is, they exhibit convergence.

All vampires, for example, are relatively small in size. The largest appears to be the common vampire bat,
Desmodus rotundus,
tipping the scales at just under an ounce and a half (around forty grams). The reasons for this size constraint are apparently related to my Trinidadian mentor Farouk Muradali's mantra, “Feeding on blood is a tough way to make a living.” In that regard, the more of the red stuff a vampire requires each day (or night), the less likely it is to obtain it. On a related note, larger vampires would need to drain greater volumes of blood from their hosts, which would increase the likelihood of weakening them to the point of death—a maladaptive trait for a parasite. Additionally, large vampires would be easier to detect by their prey as well as their predators, therefore tending to neutralize another characteristic that all vampires share: stealth. This ability to avoid detection is employed in a variety of ways by blood feeders, both during their approach to a potential meal and during the actual feeding.

The list of convergent characteristics goes on.

All blood feeders also possess finely tuned sensory systems. These allow creatures as different as bed bugs and vampire bats to efficiently locate their potential meals, often in the absence of light.

Additionally, once vampires have situated themselves within striking distance, they inflict relatively painless bites with an array of razor-sharp cutting instruments. These include denticles (leeches), chelicerae (mites, ticks, chiggers), needlelike stylets (mosquitoes and other insects), and actual teeth (vampire bats). The sharpened nature of these structures allows the vampires to gain access to the blood of their hosts without causing alarm, but even so, the complications encountered during a blood meal are
far
from over.

One major problem that all vampires must overcome is hemostasis, or blood clotting. This process actually consists of a maddeningly complex cascade of chemical reactions that must occur before a clot forms.
^*153
For the creature carrying around all that blood, the key benefit to this hemostatic complexity is that it prevents blood from clotting where and when it shouldn't. The downside to the clotting cascade is that it has enabled blood feeders to interfere with the clotting process at multiple points along the chemical pathway. In other words, if there were only one step in the clotting process where the potential blood feeder could thwart the process, the odds of evolving that ability would be pretty low. But if blood clotting can be disrupted at any one of many points in a complex chemical cascade, the odds would be much higher that such a clot-disrupting substance would evolve. As a result, although each vampire has its own separately evolved anticlotting substances, the outcome is identical—freely flowing blood from the prey, with clot formation delayed until after (sometimes
long
after) a blood meal has been obtained.

Considering how long their “manufacturers” have been in business, these natural anticoagulants are often far more efficient than anything produced by man, and several of them have become important medications. For example, the clot-dissolving properties of the vampire bat–derived substance desmokinase have been used to combat strokes, while hirudin, an anticoagulant found in leech saliva, is used to prevent blood clots from forming after hip replacement surgery. Additional vampire-derived compounds (like anesthetics, perhaps) have tremendous potential for use in the field of medicine and we can certainly expect to hear more about them as researchers explore the field.

But besides a potential for providing us with some useful pharmacological products, do blood feeders provide any additional benefits?

The answer is most certainly yes.

Vampire bats remain great examples for learning about the pitfalls of scientific discovery, especially how problems can arise when prejudice and misinterpretation substitute for careful observation and experimentation. Unfortunately, some of these early errors have perpetuated a slew of misconceptions about bats (although the next time someone implies that most bats are blood feeders, you'll be ready to pounce). Each year, thousands upon thousands of beneficial bats are killed because of fear and ignorance, and the problems that do exist with vampire bats (generally,
Desmodus
) are actually the result of man's destruction of the natural environment, combined with our dogged insistence on propagating domestic animals in places where they just don't belong.
Desmodus
and its cousins,
Diaemus
and
Diphylla,
display an amazing array of adaptations for their blood-feeding lifestyles and as such they are poor representatives for bats as a group. Far more typically, bats help reduce the number of harmful insects, pollinate plants that are essential to their ecosystems (and to humans), and help to reforest tropical regions shattered by slash-and-burn agriculture.

On another very important level, sanguivores provide food for a variety of other creatures. Leeches, for example, are a preferred meal of many species of freshwater fishes, a fact hasn't gone unnoticed by the fishing bait industry (one company offers a discount for leech orders over twenty-five pounds). Fishermen use leeches to catch game fish such as walleye
(Sander vitreus),
smallmouth bass
(Micropterus dolomieu),
and northern pike
(Esox lucius),
as well as smaller pan fish like bluegills
(Lepomis macrochirus).
Mosquitoes are another important food source, especially for birds and bats.
^*154
Mites, ticks, and chiggers are also eaten, and even bed bugs are food for some insects, including several species of ants.

Although I'm unaware of any studies on this issue, it's likely that blood feeders also serve an additional ecological role: namely, to cull out the old and the sick from prey or host populations. A moose that is able to emerge alive from a winter's stint as a “ghost moose” might very well be carrying around a genetic blueprint with an amped-up emphasis on surviving harsh conditions (especially since the ticks do not feed on the moose during the summer). On the other hand, moose that die from winter tick infestations apparently do so from starvation (distracted from feeding by all that grooming and rubbing). Hypothetically at least, not only might that moose be carrying “inferior” genes, but its death would leave more food for heartier individuals and those unaffected by the tick onslaught.

Rather than wishing for blood-feeding creatures to disappear, or starting to twitch at their very mention, we should be dealing with the fact that vampires
are
here and they're probably here to stay. In that regard, some of these blood-feeding creatures, like mosquitoes, can be deadly enemies and should be treated as such—although I am certainly not advocating the wholesale application of pesticides. Other sanguivores, like the common vampire bat, bed bugs, ticks, and chiggers, can become serious problems—some of them with the potential to sicken or even kill us. We should keep in mind, however, that in most cases these vampires would rather be feeding on something other than humans and it's generally
our fault
when we encounter them.