Dark Banquet - Bill Schutt [95]
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),