Chapter 12 – Evolution of Blood-Feeding Arthropods

The death’s-head moth displaying its skull-like thorax is the quintessential symbol of death. In reality, from the insect’s point of view, it is probably only an attempt to frighten potential predators. It certainly has that effect on humans. The death’s head moth became the symbol for human evil as embodied in Hannibal Lector, the demented serial killer in the movie Silence of the Lambs, in which the death’s head moth featured prominently. Indeed, our fascination with people who commit mass murders seems to know no end. We flock to movies about them, and follow TV shows like Dexter that attempt to cast serial killers in a semi-positive light even as the bodies pile up. And, of course, when it was time to write a paper in the forensic science class Dr. Susan Fisher used to teach, the favorite topics by far were Jeffrey Dahmer or John Wayne Gacy or Ted Bundy—our most prolific human serial killers. But if we are truly impressed by carnage, then our fascination should not be directed towards human serial killers who, at most, may dispatch a couple of dozen people. Instead, we should think of insects, particularly blood-sucking insects that share a disturbing number of characteristics with human serial killers—like sneaking up behind you, slicing you with a sharp object, and drawing blood. But, in contrast to human serial killers, the arthropod version is responsible for millions of deaths around the globe and throughout history.

Now to be clear, mosquitoes and other blood-sucking arthropods do not kill people by bleeding them dry. Most of the time, each individual blood meal is a fraction of an ounce (or a few µL). Some “back of the napkin” calculations have estimated it would take around 200,000 mosquitoes (feeding simultaneously) to drain enough blood to do serious harm to an average sized adult human. And clearly there are various biological impossibilities to prevent this actually happening. But many hematophagous (blood-feeding) arthropods do pose a serious risk to human health because of their propensity to spread pathogens while feeding. This deadly aspect of blood-feeding is the topic of the next chapter.

For now, the topic of insect serial killers begets an immediate question, namely, why are there so darn many of them scattered across so many orders of insects and non-insect arthropods? We think it is worth considering why blood feeders are so well-represented in Phylum Arthropoda, and what it would mean to earn a living by drinking the blood of another organism. What kind of challenges would confront an organism trying to make a living off of some other animal’s blood? What kind of adaptions would be needed to be successful making a living out of blood feeding?

When thinking about organisms that consume blood, a lot of the usual suspects come to mind, such as mosquitoes and fleas and bedbugs and flies. However, there are some other insects that specialize in blood-feeding that aren’t so well known. For instance, there’s a moth that eats blood, and at least one true bug, namely Rhodnius (which unfortunately spreads Chagas disease). And, of course, blood feeders are not limited to insects. We have blood-feeding ticks, mites, and spiders. Then there are the non-arthropods, such as leaches and their distant cousins, worms. Among vertebrate blood-feeders, we have vampire bats, of course, and, last but certainly not least, humans.

Yes, sometimes humans practice hematophagy. In fact, in some human cultures, the ingestion of animal blood is quite normal. The Maasai in Africa, for instance, mix animal blood with milk as a nutritious drink. In some cultures, black pudding is made by mixing animal blood with pudding. Blood is also consumed for ritualistic purposes in some religions and in some militaristic rites. And clearly there is no shortage of fascination (as evidenced by the numerous books, movies, and TV shows on the subject) in the forcible extraction of blood from living humans by other humans, a.k.a. vampirism.

Despite the distribution of hematophagy among many groups of animals, including humans, the insects have shown a devotion to blood feeding that is without rival. Blood feeding appears to have evolved nine separate times among the biting flies alone. And, as mentioned already, blood feeding is found in ticks, spiders, and trilobites in addition to the major orders of insects. Since the use of blood as a food source requires, at a minimum, the interaction of two disparate species of animals, it is of interest to know how such an arrangement might have evolved in the first place.

Evolution of Blood Feeding

In all ecological relationships that involve multiple species, one of the challenges is to understand not only why such relationships are common, but to consider how they evolved in the first place. In the case of blood-feeding, there are two general hypotheses adduced to explain its evolutionary origins. The first of these is the idea that blood feeding could have evolved between arthropod and vertebrates species with the arthropod initially just seeking refuge in the nest of the vertebrate. Think about the burrows of rodents, for instance, or the nests of birds. A non-blood feeding arthropod may have sought shelter in the nest of the vertebrate where it would be somewhat protected from the elements, and would also be provided with a source of warmth to extend the length of its activities after cold weather arrived. Recall that arthropods are ectothermic and cannot generate their own heat endogenously. However, if they could siphon off some thermal energy from a vertebrate host, they could remain active later in the year.

Once ensconced in a vertebrate home, it is very likely that the nest-bound arthropods would have sought a local food source. Evolutionary biologists think that this might have begun simply by scavenging on hair, feathers, dander (cast off skin), and host secretions of various sorts. The aforementioned materials do have some nutritional value but, compared to the river of blood lurking just under the skin of the vertebrate host, it is paltry indeed. So, natural selection would have favored any mutation that would have allowed the arthropod to breech the skin and reach the blood. Here, mutations that changed the arthropod mouthparts to something that could abrade the skin and allow it to sop up the resulting pool of blood would have rapidly increased in proportion. At that point, the arthropod would have had the choice of continuing to feed on hard-to-digest materials like hair and feathers that have low nutritional value, or switching to blood. Clearly, the latter was preferred.

The second hypothesis advanced to explain the evolution of blood-feeding is that prior to establishing a relationship with a vertebrate host, the arthropods may have undergone random mutations that preadapted them for a blood-feeding lifestyle. In other words, the trait that made arthropods successful blood feeders arose by chance in some populations of arthropods and/or became more abundant in response to another specific selective pressure. However, if an insect with such a mutation happened to land on a vertebrate host, it would be more likely to become a successful blood-feeder. This sounds rather fanciful, so it is important to ask whether there is any evidence that such a thing took place. And the answer is “yes.” For instance, scorpionflies are plant feeders (Figure 12.1). They use their long proboscis to pierce the cuticle of plants and withdraw plant fluids as their food source. Such mouthparts are ideally suited to piercing vertebrate skin and withdrawing blood. The fact that scorpionflies and fleas share a common ancestor suggests that the general design of the mouthparts might be suitable for plant-feeding or blood-feeding. It could have been simply a matter of chance that caused the two groups to go in different ways.

Another interesting example of this phenomenon is the vampire moth. Clearly, blood-feeding among moths is a rare thing (thank goodness!). But, it appears that the vampire moths’ heavily sclerotized mouthparts augmented with erectile barbed hooks that it uses to pierce the thick rinds of melons may have preadapted it for blood feeding. In a strict biological sense, we would consider vampire moths to be opportunistic blood-feeders. Most of the time, vampire moths feed on plants. But, every so often, if one lands on an attractive vertebrate host, it will use those same mouthparts to pierce the skin and withdraw blood. National Geographic has thoughtfully provided a video of a vampire moth doing its best to extract a blood meal from some cooperative humans (Video 12.1). This species was formally known only to feed on fruit, but given the opportunity, it readily fed on blood. Thus, the idea of preadaptation appears to have legitimacy.

Challenges of Blood-feeding

Given the widespread distribution of blood feeding, the next question we need to confront is how the arthropods that use blood surmount the multiple challenges attendant to a blood-feeding habit. For instance, small organisms like insects that specialize in blood have to have the ability to take on a huge volume of fluid, extract the nutrients they need, and discard the rest. The invertebrate blood feeders also must find a host. As we shall see, this is a process that has produced some very sophisticated and often ingenious ways of locating and invading a host. Nearly all blood feeders have specialized mouthparts that are adept at piercing skin and withdrawing the fluid we know as blood. And, in any given group, there can be a variety of ancillary adaptations designed to keep the blood moving, preventing clotting, or making the host more cooperative.

As an example of the aforementioned challenges, imagine that you’re a deer tick. For most of your life, your body is about the size of the tip of a pencil eraser. But if you’re a female and you are getting ready to produce eggs, you need to take on a blood meal, the volume of which will increase your size as much as 100-fold. In fact, unfed and engorged females hardly look like the same species (Figure 12.2). Imagine further that a human was given this assignment. Imagine what your body would look like if it had to increase in size 100-fold in 10–14 days (e.g. you went from weighing 150 lbs to weighing 15,000 pounds!). And then you had to shed all of that biomass also in a very short time. What kinds of strains and stresses would occur? What kind of adaptations would you need to accomplish this?

As must be obvious, blood-feeding arthropods face a litany of challenges. The challenges are so numerous, in fact, that they can be divided into 10 discrete identifiable groups. All of these have been overcome by one or more arthropod groups in order to have a lifecycle that is predicated upon using the blood of another organism as its main food source. We will now address each of the challenges individually.

Challenge 1: Locating a Host

Finding a vertebrate host can be a significant challenge for the blood-feeder. Unless the host is something like a cow, chicken, or pig, which are often grown in large numbers in the same area, the typical vertebrate host will be randomly and sparsely distributed across the landscape. It is advantageous, therefore, to have some cue that emanates from the host which the arthropod can hone in on to help them locate their blood meal.

Since all vertebrates emit carbon dioxide (CO₂) as part of their intermediary metabolism, arthropods often use it as a mechanism for finding a host. Other metabolic cues, such as water vapor, butanol, or lactic acid can serve this purpose as well. Some arthropods have gone in the direction of using body odors as a mechanism for tracking a host. In this case, “smelly” secretions such as sweat, urine, or feces can be used to locate the elusive vertebrate host.

The female mosquito, for example, has up to 72 chemoreceptors in her repertoire, of which approximately 27 are involved in host location. Using CO₂–detecting chemoreceptors, the female will locate a host, which could be you! But she might not choose you because mosquitoes like the way some people smell better than others. Indeed, there are preferred combinations of odorants found in sweat that attract mosquitoes to some people more than others.

Finally, some arthropods use vision as a means for finding a host. However, this only works during the daytime. As a result, visual location of hosts is less common among blood-feeders and is often used only after a chemical attractant coming from the host has brought the blood-feeder into proximity with the host.

Challenge 2: Finding a Blood Vessel

If you have ever had a sample of your blood drawn for analysis, you know that this is a tricky job. In order to get your blood, the phlebotomist will wrap a tourniquet around your arm and tighten it to make a blood vessel protrude. You may also be asked to squeeze a ball with your hand to make the vein more visible. Only then will the phlebotomist come at you with a needle and, even then, the quest may not be successful if your veins are collapsed or you are dehydrated, etc. The blood-feeding arthropod has the same problem, but without the technological fixes that humans have at their disposal. So, how do they manage to find and extract your blood?

One solution is to avoid the problems listed above by simply slashing open the skin of the vertebrate with sharp, razor-like mouthparts. This process is sufficiently violent that it will rupture small blood vessels creating a pool of blood on the skin which can then be sopped up with sponge-like mouth parts. Of course, this approach to blood-feeding has a significant disadvantage in that in hurts to have one’s skin ruptured in this way, and the encounter will alert the host to the presence of the arthropod. Many vertebrates will cue-in on the sound (if any) made by the approaching blood-feeder and use this sound as a motivator to leave the area. Think, for instance, of Tabanid horseflies. The sound produced by the approaching fly is enough to send the intended victim off at a gallop.  Other potential hosts will use the sensation of the mouthparts entering the skin as a signal to bite at or otherwise dislodge the arthropod, which makes it difficult to sop up the pool of blood created on the vertebrate’s skin.

As a result of these difficulties, some blood-feeders have gone to great lengths to make their approach and subsequent activities less detectable. Blood-feeders such as mosquitoes, for instance, are often more active at night when the host is likely to be asleep and, therefore, less likely to detect the blood-feeder. Another solution is to have detectors that allow the blood-feeder to rapidly find a subcutaneous blood vessel and specifically tap into it. Some blood-feeders have chemoreceptors on their mouthparts or antennae that allow them to use a host-derived chemical to hone in on the location of a capillary bed. Others have thermoreceptors that allow them to use host-derived heat for this purpose.  Heat generated by the host increases probing to locate a blood vessel. Since these blood-feeders are a lot more specific in their approach, they cause less pain when they enter the skin and are, therefore, less likely to be detected. Some blood-feeders even go to the trouble of producing pain-killers with which they anesthetize the skin prior to inserting their mouthparts!

Challenge 3: Getting the Blood Out

Once the blood-feeder has located the host and identified its blood supply, it still has some challenges to face. It has to get the blood out of the host and into its alimentary canal, for instance. As previously noted, a very basic way of doing this is to simply slash open the vertebrate’s skin and let the blood flow until the host’s clotting mechanisms kick in and staunch the bleeding. The blood-feeding arthropod then soaks up the pool of blood with sponge-like mouth parts. The scientific name for this approach is telmophagy (derived from the Greek: telmo = pool and, of course, phagy = eat). But even this relatively primitive approach to blood-feeding has some nuances. For instance, some arthropods are macropoolers meaning that they create a big pool of blood. An example of this approach is the previously mentioned tabanid horse flies, which use knife-like mouthparts to slash open the skin. Other telmophagic forms are the more discrete micropoolers, which also lacerate the skin of the host with their mouthparts but, in contrast to the macropoolers, only produce a small pool of blood. An example of this approach is found among the biting midges who keep their blade-like mouthparts inside a fleshy sheath until they are needed, at which point they emerge and lacerate the host’s skin.

We’ve already discussed the problems attendant with telmophagy, namely, the host rapidly detects the presence of the blood-feeder and takes evasive action. As a result, a second more advanced approach to securing a blood meal has arisen among blood-feeders, and that is to tap directly into a blood vessel. In a process called solenophagy (soleno is Greek for vessel), these blood-feeders show a variety of adaptations to facilitate this approach. In solenophagic arthropods, the mouthparts have been redesigned to allow the insect to penetrate the skin and directly pierce a blood vessel. As a result, the mouthparts are often long and slender, sort of like a hypodermic needle. Solenophagic species vary in the details of how they feed. Some slash open the blood vessel—this is similar to telmophagy, but is focused on a blood vessel rather than a patch of skin. Others cannulate the vessel (insert a narrow tube into a body part) which is quite a bit more precise then the other modalities discussed. Cannulating solenophages are more subtle and cause less tissue damage. Thus, they are less likely to be detected by the host and are more likely to be able to blood-feed for an extended period of time. Mosquitoes are an example of a type of organism that has invested in multiple adaptations to facilitate a solenophagic lifestyle. A mosquito can very precisely cannulate a blood vessel with its long, needle-like proboscis (Figure 12.3 – click on link)

While other insects slash your skin indiscriminately, the mosquito sets a very nuanced standard. She will gently insert her proboscis into your skin, exuding as she does a bit of anesthetic to prevent you from noticing and brushing her away. And her proboscis doesn’t wander willy-nilly under your skin. Oh no, she has a very precise goal in mind: to locate and penetrate a capillary. All this she does without leaving a trace of blood on your skin.

Challenge 4: Preventing Coagulation of Blood

One persistent challenge in the blood-feeding lifestyle is that vertebrates are elegantly designed with sophisticated clotting mechanisms that will seal up holes and stop any bleeding. Thus, when an arthropod invades the sanctity of a blood vessel or, even worse, rips a hole in the skin and severs many capillaries in the process, a host of biochemical reactions are set into action that will plug the breech and restore homeostasis. To the arthropod, this means that the opportunity for extracting a blood meal is very limited. As soon as the hole is sealed, the flow of blood will stop and the meal will be gone. As mentioned previously, enterprising arthropods such as mosquitoes have surmounted this problem by secreting anticoagulants in their saliva. When they bite a vertebrate, the saliva and anticoagulant enter the blood vessel, prevent clotting, and thereby extending the time during which the female can blood-feed. This is another reason why females are most active at night, when you are less likely to perceive the invasion and swat her. It is all very ingenious.

Challenge 5: Host Irritation

Think back to a time when you poked yourself with a thumbtack or mistakenly backed into a nail. You know immediately that you’ve done something dumb because it hurts! Your next reaction will be to turn around to see what hurt you and then consider when your last tetanus shot was given. With an insect bite, the pain may attract your attention and incite you to do something bad to the insect. The breech of your skin will also initiate an immune response which, in conjunction with coagulation, will seal the wound. Thus, the opportunity for getting the blood meal is time-limited.

Some insects don’t care whether their slash and burn approach to blood-feeding incites your wrath. These are the ones that just tear open the skin and let you bleed. Even if they are swatted away following the initial breech, they will come back to sop up the pool of blood. However, a more advanced solution to this problem is to secrete anti-inflammatory substances when they bite you. This reduces the immune response and the pain of the bite, making it less likely that you will detect the arthropod and engage in a little dorsal-ventral compression of the bug to get rid of it.

Challenge 6: Expanding Body Mass

Many blood-feeders are temperate in their blood-gathering habit and take small blood meals that are sufficient to the moment. However, arthropods that require a blood meal to reproduce need to take on larger quantities of blood in order to gain enough nutrients to produce and nourish offspring. This creates further problems for the arthropod.

Among mosquitoes, for example, only the females ingest blood and their purpose, not surprisingly, is to use it to create a large batch of hundreds of baby mosquito eggs. But as we learned in the chapter about growth and development, insect exoskeletons are typically rigid and must be shed in order for them to increase in size. However, some insects have developed a creative solution to this problem. In this case, the female’s abdomen contains a special elastic protein called resilin that acts like a rubber band and allows her abdomen to expand massively to accommodate a large blood meal (Figure 12.4). But an engorged female mosquito (or other insect) now faces new challenges.

Challenge 7: Discarding Unneeded Stuff and Reducing Body Size

A massively expanding abdomen is only the first problem that this method of reproducing entails. Engorged insects are less mobile and highly vulnerable to predation. Perhaps you have seen engorged female ticks lying on the sidewalk because they have fallen off the host in an inopportune spot after taking on a meal. The usual human response is to squash them to get rid of them for good.

Ultimately, the solution to the arthropod’s post-blood-feeding body size is to reduce it. Again, arthropods have proven to be very clever in the mechanisms they use to handle this radical change in the milieu interior. They are able to kick their Malpighian tubules (remember those?) into high gear to separate water and salts from blood and then excrete them to reduce the size of the abdomen. They also have very efficient mechanisms to metabolize the nutritious components of the blood and shunt them rapidly into egg production. Ticks have even added the ability to “spit” unneeded components of blood back into the host with their saliva which is a creative if a bit rude solution to this problem. It is also how they transmit pathogens that make us sick like the bacteria that causes Lyme disease or viruses that cause Rocky Mountain spotted fever.

Female mosquitoes also face this risk—having a large, swollen abdomen makes her less able to fly and more vulnerable to predators (including you). Consequently, mosquitoes have evolved the ability to quickly separate the components of blood and excrete excess fluid to reduce her size, while concentrating the nutrients she will need for reproduction. Furthermore, after feeding, mosquitoes will often alight in an out-of–the-way place, like the ceiling, to avoid being killed while still in this vulnerable state. In short, the female mosquito is a marvel of adaptation, all of which are designed to achieve success in blood-feeding.

Challenge 8: Digesting the Blood Meal

The next problem is biochemical in nature. Blood is a highly specialized fluid whose composition can vary from species to species. There are even mosquitoes that feed on the viscous cold blood of snakes, frogs, and turtles! Since blood feeders may or may not choose a single species as a food source, the arthropod has to be prepared to metabolize blood of varying composition. Add to that the reality that they may ingest so much blood that normal metabolism will not be able to solve the problem quickly enough. In this case, some arthropods have the ability to upregulate their digestive enzymes in the midgut to meet the increased metabolic demands of a large blood meal. What this means is that arthropods will make additional copies of blood-metabolizing enzymes by turning on the transcription and translation of genes that produce these enzymes so that more copies can be made. If the female survives beyond egg-laying, the production of these enzymes can later be downregulated so that she is not producing unneeded enzymes. In short, these arthropods have a very sophisticated system of “on demand” enzyme production.

Challenge 9: Heme Toxicity

While we have been addressing blood as the holy grail of insect nutrition, it turns out that that is an oversimplification. Particularly in the case of females who will take on a very large blood meal prior to egg production, a significant problem can occur during metabolism of the blood. Vertebrate blood is full of a protein called hemoglobin, as we discussed in Chapter 2. In fact, hemoglobin is the most abundant protein in blood, and is what gives blood its nutritional content. Hemoglobin, itself, is rather complex. It is actually composed of four strands of protein held together by a heme molecule (Figure 12.5 – click on link). Heme, in turn, is a large molecule with an iron atom at its center. When the blood is metabolized by the arthropod, the protein chains that make up the hemoglobin are broken down and the products absorbed by the arthropod. In the process, heme is released from the protein and if it accumulates in high amounts, as it potentially would with a large blood meal, the heme can be toxic to the arthropod.

How can the arthropod avoid being intoxicated by its required food source? Again, arthropods have proven to be highly creative. They have a mechanism for packing the unneeded but toxic heme molecule into vesicles in the midgut which sequesters them and prevents them from being toxic.

Challenge 10: Chronic Nutritional Deficiencies

I (S.W. Fisher) had a friend in high school who worked at a pizza place and who ate nothing but pepperoni. He loved pepperoni and, since he could get it for free, he ate a lot of pepperoni and very little of anything else. He figured it had a lot of protein and would be a good source of nutrition. Then, after a few months of doing this, his gums began to bleed. He went to see his doctor and discovered that his high pepperoni diet may have supplied him with adequate protein but did not carry enough of other required nutrients to keep him healthy. Pepperoni has, for instance, no Vitamin C, which is an essential nutrient for human beings. As a consequence, his gums started to bleed—the classic sign of scurvy, and a direct result of a diet depauperate in Vitamin C. In fact, this is a condition that is so rare among modern humans that scurvy is typically associated with sailors who are out to sea for months at a time and had no access to fresh fruit—a major source of Vitamin C.

The typical blood-feeding arthropod is not unlike Dr. Fisher’s pepperoni-eating friend. Such arthropods have a diet that is very high in protein but is utterly deficient in key nutrients that their bodies also need in order to function. Among the things that blood lacks are key carbohydrates, lipids, and B Vitamins. How can blood-feeders overcome this problem? One way they can do this is to feed on other things when not busy reproducing. A lot of blood-feeding insects feed on plants or other sources for a significant part of their lifecycle, which supplies them with the nutrients they cannot obtain through blood-feeding. They switch to blood-feeding only when they need to engage in it, which often means only for the purpose of reproduction. This is true for insects such as mosquitoes and fleas. 

Other arthropods are more closely tied to the host and to blood-feeding; they only ever feed on blood and cannot switch to eating plants even if it means foregoing key nutrients. This includes arthropods like bed bugs, kissing bugs, lice and ticks. One way those arthropods survive on a protein-only diet is to acquire endosymbionts such as bacteria and archaens that live in their gut. These organisms, in exchange for room and board, manufacture the nutrients that the arthropods are not getting in their diets. Again, this is a very creative solution to an apparently intractable problem.

Chapter Summary

The take home message from this chapter is that arthropods have shown great resilience and creativity in negotiating the demands of a blood-feeding lifestyle. This is likely because blood feeding evolved multiple times among arthropods, in some cases because the arthropods lived in close proximity to vertebrates and in other cases because they had mouthparts adapted for getting juices out of plants or other arthropods, and also because arthropods feed on such a variety of vertebrate hosts. Over evolutionary time arthropods were knited closely to their vertebrate host, and evolved a incredible number of adaptations that allowed them to find, ingest, and digest blood. As we discussed here, using blood as a food source is fraught with problems, but arthropods have the genetic plasticity to endlessly test new combinations of genes so that, in the end, the problems have been allayed and a very large number of arthropod groups have been able to use this unlikely food source as their mainstay of existence.  This is a theme we will revisit in future chapters.

References

Chapter 12 Cover Photo: Death’s-head hawkmoth.  CC-BY 2.0: Coleman, W. S.; E. Smith; J. G. Wood; and T. W. Wood.  Accessed via commons.wikimedia.org

Figure 12.1: Male scorpionfly.  CC-BY 2.0: gailhampshire.  Accessed via https://commons.wikimedia.org/wiki/File:Scorpion_Fly._Panorpa_communis._Mecoptera_(7837166610).jpg

Figure 12.2: Deer ticks.  CC-BY-SA 3.0: Alan R Walker.  Accessed via https://commons.wikimedia.org/wiki/File:Ixodes-ricinus-life-cycle.jpg

See also: http://www.tickencounter.org/tick_identification/tick_growth_comparison

Figure 12.3: Mosquito mouthparts.  Image from DK Insect Guides – Amazing Bugs, by Miranda Macquitty.  Available at https://www.reverbnation.com/page_object/page_object_photos/artist_2303956?photo=8406312 

Figure 12.4: Female mosquito feeding.  CC0 Public Domain: skeeze.  Accessed via https://pixabay.com/en/mosquito-biting-female-parasite-542156/

Figure 12.5: Hemoglobin and heme molecule.  Author unknown.  Available at https://forgottenphysiology.com/2014/06/

Video 12.1: Vampire moth feeding.  National Geographic.  Available at http://video.nationalgeographic.com/video/news/vampire-moth-vin?source=relatedvideo

Additional Readings

Lehane,  M. (2005).  The Biology of Blood-Sucking Insects.  Cambridge University Press, Cambridge, UK, 312 pages.

Zinsser, H. (1963).  Rats, Lice and History.  Little, Brown, Boston.