Vampires have fascinated us since the Middle Ages, when a hysteria of vampire sightings spread across Eastern Europe. We now know that many of these “vampires” were actually victims of diseases like tuberculosis or bubonic plague that cause bleeding in the lungs (and elsewhere), resulting in the disturbing effect of blood appearing at the lips. Add this attribute to the already poorly understood physiology of decomposing corpses and the cases in which people mistakenly buried alive got up and left their graves, and voila! Vampire mythology is born. So vampires don’t really exist… Or do they?
Actually, there are many animals that feed on blood. So many in fact, that there is a scientific term for blood-eating, hematophagy. And why not? Blood is fluid tissue, chock full of nutritious proteins and lipids and a source of water to boot. And if you don’t kill your prey to feed, the food supply replenishes itself. Here are just some of these animal vampires living among us:
Vampire bat
A vampire bat smiles for the camera
from his Peruvian cave. Photo from Wikimedia.
Vampire bats are our most famous animal vampires, and the ones that most resemble our vampiric lore. There are three species of vampire bats that live from Mexico down through Argentina. Two of them, the hairy-legged and white-winged vampire bats, feed mostly on birds. The common vampire bat feeds more on mammals, like cows, horses, and the occasional human. Their razor sharp teeth cut a tiny incision in their victims and their anticoagulant saliva keeps the blood flowing. Like Dracula, vampire bats sleep by day and hunt by night. But these vampires are not loners like Dracula: They live in colonies of about 100 animals, and in hard times will share their blood-harvest and care for one another’s young.
Vampire finch
The Galapagos Islands are the famous home to numerous finch species, each one with a beak shape specially adapted to their preferred food source. For most of these finches, their food of choice is a type of seed or nut that is appropriately sized for their beak shape and strength. But the vampire finch (also called the sharp-beaked ground finch for obvious reasons) uses its long sharp beak to feed on blood. Their most common victims are their booby neighbors (named for less obvious reasons).
Candirú
A tiny candirú catfish (being measured in cm) strikes
terror into the souls of Amazonian fishermen.
Photo by Dr. Peter Henderson at PISCES Conservation LTD.
Photo at Wikimedia.
The tiny Amazonian candirú catfish is legendary for one documented case (and several undocumented ones) in which a candirú swam up a local man’s urine stream into his penis, where it attached to feed on his blood. Although terrifying, this is not typical candirú behavior. Actually, it was all just a misunderstanding. You see, candirú catfish do feed on blood, but they usually feed from the highly vascularized gills of other Amazonian fish. As we saw last week, the gills of freshwater fish release high quantities of urea, a major component of urine. So to a hungry candirú, your pee smells an awful lot like a fish-gill blood dinner. Just another reason to not pee where you swim.
Lamprey
Notice the sharp-toothed sucker mouth of the river
lamprey. Photo by M. Buschmann at Wikimedia.
Lampreys are species of jawless fish. With their eel-like bodies and disc-shaped mouths filled with circles of razor-sharp teeth, they look like something from science fiction horror. Although some lamprey species are filter feeders, others latch onto the sides of other fish, boring into their flesh and feeding on their blood. Once attached, they can hitch a ride on their victim for days or even weeks.
Leech
A European medicinal leech.
Photo by H. Krisp at Wikimedia.
Leeches are the earthworm’s bloodsucking cousins. With three blade-like mouthparts, they slice into their victims, leaving a Y-shaped incision. They produce anticoagulants to prevent premature clotting of their bloodmeals, which can weigh up to five times as much as the leach itself. The bloodletting and anticoagulant abilities of leeches have led them to be used medicinally in ancient India and Greece as well as in modern medicine.
Female mosquito
A female mosquito getting her blood meal.
Photo by at Wikimedia.
Most of the time, mosquitos use their syringe-like mouthparts to feed on flower nectar. But when the female is ready to reproduce, she seeks out a blood meal to provide the additional protein she will need to produce and lay her eggs. Although their bites only cause minor itching, these lady vampires are truly something to be feared: They kill more people than any other animal due to the wide range of deadly diseases they spread.
There are many other examples of animals that feed on blood. But unlike their mythological counterparts, none of them come back from the dead to do so… Or do they?
Happy Halloween!
Want to know more? Check these out:
1. SCHLUTER, D., & GRANT, P.R. (1984). ECOLOGICAL CORRELATES OF MORPHOLOGICAL EVOLUTION IN A DARWINS FINCH, GEOSPIZA-DIFFICILIS EVOLUTION, 38 (4), 856-869
2. Francischetti, I. (2010). Platelet aggregation inhibitors from hematophagous animals Toxicon, 56 (7), 1130-1144 DOI: 10.1016/j.toxicon.2009.12.003
Several animals, many of them insects, crustaceans and fish, can smell when their fellow peers are scared. A kind of superpower for superwimps, this is an especially useful ability for prey species. An animal that can smell that its neighbor is scared is more likely to be able to avoid predators it hasn’t detected yet.
“What does fear smell like?” you ask. Pee, of course.
I mean, that has to be the answer, right? It only makes sense that the smell of someone who has had the piss scared out of them is, well… piss. But do animals use that as a cue that a predator may be lurking?
Canadian researchers Grant Brown, Christopher Jackson, Patrick Malka, Élisa Jaques, and Marc-Andre Couturier at Concordia University set out to test whether prey fish species use urea, a component of fish pee, as a warning signal.
A convict cichlid in wide-eyed
terror... Okay, fine. They're
always wide-eyed. Photo by
Dean Pemberton at Wikimedia.
First, the researchers tested the responses of convict cichlids and rainbow trout, two freshwater prey fish species, to water from tanks of fish that had been spooked by a fake predator model and to water from tanks of fish that were calm and relaxed. They found that when these fish were exposed to water from spooked fish, they behaved as if they were spooked too (they stopped feeding and moving). But when they were exposed to water from relaxed fish, they fed and moved around normally. Something in the water that the spooked fish were in was making the new fish act scared!
To find out if the fish may be responding to urea, they put one of three different concentrations of urea or just plain water into the tanks of cichlids and trout. The cichlids responded to all three doses of urea, but not the plain water, with a fear response (they stopped feeding and moving again). The trout acted fearfully when the two highest doses of urea, but not the lowest urea dose or plain water, were put in their tank. Urea seems to send a smelly signal to these prey fish to “Sit tight – Something scary this way comes”. And the more urea in the water, the scarier!
But wait a minute: Does this mean that every time a fish takes a wiz, all his buddies run and hide? That would be ridiculous. Not only do freshwater fish pee a LOT, many are also regularly releasing urea through their gills (I know, gross, right? But not nearly as gross as the fact that many cigarette companies add urea to cigarettes to add flavor).
The researchers figured that background levels of urea in the water are inevitable and should reduce fishes fear responses to urea. They put cichlids and trout in tanks with water that either had a low level of urea, a high level of urea, or no urea at all. Then they waited 30 minutes, which was enough time for the fish to calm down, move around and eat normally. Then they added an additional pulse of water, a medium dose of urea, or a high dose of urea. Generally, the more urea the fish were exposed to for the 30 minute period, the less responsive they were to the pulse of urea. Just like the scientists predicted.
A rainbow trout smells its surroundings.
Photo at Wikimedia taken by Ken Hammond at the USDA.
But we still don’t know exactly what this means. Maybe the initial dose of urea makes the fish hide at first, but later realize that there was no predator and decide to eat. Then the second pulse of urea may be seen by the fish as “crying wolf”.
Alternatively, maybe the presence of urea already in the water masks the fishes’ ability to detect the second urea pulse. Or maybe both explanations are true.
Urea, which is only a small component of freshwater fish urine, is not the whole story. Urea and possibly stress hormones make up what scientists refer to as disturbance cues. Steroid hormones that are involved in stress and sexual behaviors play a role in sending smelly signals in a number of species, so it makes sense that stress hormones may be part of this fearful fish smell. But fish also rely on damage-released alarm cues and the odor of their predators to know that a predator may be near. Scientists are just starting to get a whiff of what makes up the smell of fear.
Want to know more? Check these out:
1. Brown, G.E., Jackson, C.D., Malka, P.H., Jacques, É., & Couturier, M-A. (2012). Disturbance cues in freshwater prey fishes: Does urea function as an ‘early warning cue’ in juvenile convict cichlids and rainbow trout? Current Zoology, 58 (2), 250-259
2. Chivers, D.P., Brown, G.E. & Ferrari, M.C.O. (2012). Evolution of fish alarm substances. In: Chemical Ecology in Aquatic Systems. C. Brömark and L.-A. Hansson (eds). pp 127-139. Oxford University Press, Oxford.
3. Brown, G.E., Ferrari, M.C.O. & Chivers, D.P. (2011). Learning about danger: chemical alarm cues and threat-sensitive assessment of predation risk by fishes. In: Fish Cognition and Behaviour, 2nd ed. C. Brown, K.N. Laland and J. Krause (eds). pp. 59-80, Blackwell, London.
3.
Every year science bloggers from across the web come together to raise awareness and money for science education at DonorsChoose.org. Teachers send DonorsChoose their wishlists for the projects they would like to do with their students and you can choose which projects you may like to contribute to. This Science Blogger Challenge runs through November 5th. The readers of the blog to deliver the most supplies to students across the country win bragging rights for the year!
As The Scorpion and the Frog is a new blog this year, I have created the very first The Scorpion and The Frog Giving Page, listed under Proudly Independent Science Bloggers. I chose to promote four projects in high poverty areas across the country that teach students about animals in creative and inspiring ways.
Help Ms. Bakker’s high school class in Chicago, Illinois build Carnivore Scent Stations (areas with loose dirt on top and animal scent in a hole beneath to attract wildlife) and track the prints of animals that visit the stations.
Or help Mrs. Westphal’s elementary students in Astatula, Florida study food webs by dissecting owl pellets.
Or help Mrs. Maruri’s class in Pleasant Grove, Utah get dissection kits to study animal anatomy.
Or help Mrs. Scherer’s students in Detroit, Michigan study the life cycles of chickens, ducks, ladybugs, crayfish, guppies, tadpoles and butterflies by bringing the animals into the classroom to care for and to study.
Check out these awesome projects and others at DonorsChoose.org!
Donate to help passionate teachers have the resources they need to inspire our next generation of biologists! Donations of any amount make a difference and are appreciated.
An entire colony enslaved by an alien species to care for their young. Slave rebellions quelled by mind manipulation. It sounds like science fiction, right? But it really happens!
Myrmoxenus ravouxi (called M. ravouxi for “short”) is a slave-making ant species in which the queen probably wears a chemical mask, matching the scent of a host species in order to invade their nest without detection. Once inside, she lays her eggs for the host species workers to care for. Armies of M. ravouxi workers then raid these host colonies to steel their brood to become future slave-laborers to serve the needs of the M. ravouxi colony.
A M. ravouxi queen throttling a host queen. Photo by Olivier Delattre.
Enslaved worker ants could rebel: They could destroy the parasite brood or at least not do a good job caring for them. But to selectively harm the parasite brood without harming their own nests’ brood, the host ants would have to be able to tell them apart. Ants learn the smell of their colony in their youth, so any ants born to an already-parasitized colony would likely not be able to tell apart parasite ants from their own species. But what about ants that were born to colonies before they were invaded?
Olivier Delattre, Nicolas Châline, Stéphane Chameron, Emmanuel Lecoutey, and Pierre Jaisson from the Laboratory of Experimental Ethology in France figured that compared to ant species that were never hosts to M. ravouxi colonies, ant species that were commonly hosts of M. ravouxi colonies would be better able to discriminate their own species’ brood from M. ravouxi brood. Host species may even be better at discriminating in general.
The researchers collected ant colonies from near Fontainebleau and Montpellier in France. They collected M. ravouxi colonies and colonies of a species that they commonly parasitize (but were not parasitized at the time): Temnothorax unifasciatus (called T. unifasciatus for “short”). The researchers also collected T. unifasciatus that were parasitized by M. ravouxi at the time. Additionally, they collected colonies of T. nylanderi and T. parvulus, two species that are never parasitized by M. ravouxi. (Sorry guys. All these species go by their scientific names. But really, that just makes them sound all the more mysterious, right?). The researchers took all their ant colonies back to the lab and housed them in specialized plastic boxes (i.e. scientific ant-farms).
On the day of the tests, the scientists removed a single pupa (kind of like an ant-toddler) from one nest and placed it into a different nest of the same species or back in its own nest. They did this for colonies of both non-host species and for colonies of host species T. unifasciatus that were not parasitized at the time. Then they counted how many times the workers bit the pupa (an aggressive behavior) or groomed the pupa (a caring behavior).
Workers from all three species bit the pupa that was not from their colony more than they bit their own colony’s pupa. But the T. unifasciatus (the host species) were even more aggressive to foreign pupa than the other species. And only the T. unifasciatus withheld grooming from the pupa that was not from their colony compared to the one that was from their colony. Although all three species seemed to be able to tell the difference between a pupa from their own nest versus one from another nest, only the species that is regularly enslaved by M. ravouxi decreased care to foreign young.
So that is what these ants do when they are not enslaved. How do you think enslaved ants respond to their own species’ young compared to M. ravouxi young?
A 1975 cover of Galaxie/Bis, a
French science fiction magazine,
by Philippe Legendre-Kvater.
Image from Wikimedia.
The researchers repeated the study using enslaved T. unifasciatus, placing either a pupa of their own species from a different nest or a M. ravouxi pupa in with their brood. Even though prior to M. ravouxi takeover the T. unifasciatus bit foreign pupa more than their own, after M. ravouxi takeover they didn’t bite foreign pupa of their own species or M. ravouxi pupa very much. Not only that, but they groomed the M. ravouxi pupa more than the pupa of their own species! Ah hah! Mind control!
This, my friends, is the kind of truth that science fiction is made from.
But how might this work? Ants born to an enslaved colony would be exposed to both their own odors and the M. ravouxi odors. Because ants learn the smell of their colony in the first few days after they emerge from their eggs, these enslaved ants would have a broader set of smells that they may perceive as being “within the family”. That would explain why the enslaved T. unifasciatus ants didn’t attack either the foreign-born T. unifasciatus or the M. ravouxi young, but it doesn’t explain why the enslaved ants provided more care to the M. ravouxi than they did to their own species. One possibility is that the M. ravouxi produce more or especially attractive odors to encourage the host workers to take care of them.
There is still more to learn about this system: How exactly may the M. ravouxi be hijacking the pheromonal systems of their host species? How are the host species protecting themselves from exploitation? I guess we’ll have to wait for the sequel.
Want to know more? Check this out:
Delattre, O., Chȃline, N., Chameron, S., Lecoutey, E., & Jaisson, P. (2012). Social parasite pressure affects brood discrimination of host species in Temnothorax ants Animal Behaviour, 84, 445-450 DOI: 10.1016/j.anbehav.2012.05.020
Most male songbirds will sing when they see a pretty female during the breeding season. But some male songbirds sing even when it’s not the breeding season. Why do so many birds sing in fall at all?
Maybe singing feels good… But how do you ask a bird if it feels good to sing?
European starlings are one of those bird species that sing both in spring (the breeding season) and in fall (not the breeding season). Lauren Riters, Cindi Kelm-Nelson, and Sharon Stevenson at the University of Wisconsin at Madison did a series of ingenious experiments to ask starlings if and when it feels good to sing.
A European starling sings his fall-blues away. Photo by Linda Tanner at Wikimedia.
Psychologists have long used a paradigm called conditioned place preference (CPP) to evaluate whether an animal finds something rewarding or pleasurable. CPP is based on the idea that if an animal experiences something meaningless while at the same time experiencing something else that is rewarding, the animal will learn to associate these two things with each other in a phenomenon called conditioning. For example, a puppy that has learned that every time it sits it gets a treat, will find itself sitting more often.
A researcher can also compare how rewarding different types of treats are. If we want to know if puppies like carrots or steak better, we can give one group of puppies a carrot every time they sit and another group of puppies a piece of steak every time they sit. If the group of puppies that are conditioned with steak spend more time sitting, we can conclude that steak is more rewarding to puppies than carrots are.
Lauren and Sharon used this principle to ask starlings if singing is rewarding. They put spring starlings in a cage with a nestbox and a female and let them sing away, while counting how many songs they sang in 30 minutes. Then they immediately put them in another cage that was decorated with yellow materials on one side and green materials on the other, but they restricted each bird to only one of the two colored sides. This is the conditioning phase in which the bird learns to associate the colored cage with the feeling they get from singing.
The next day, they put the starlings in the yellow and green cage without restrictions so they could choose what side they wanted to hang out in. If singing is rewarding, we would expect starlings that sang a lot to spend more time on the side with the color they were placed in the day before.
Do people that sing in the car spend more time in the car?
Photo by freedigitalphotos.net.
That didn’t happen. The spring starlings spent the same amount of time in the yellow or green side of the cage regardless of how much they sang the day before.
But when Lauren and Sharon did the same test with fall starlings singing without a female, there has a huge effect: Males that sang more spent much more time on the colored side of the cage they were placed in the day before. Singing, for a male starling, is apparently rewarding in fall, but not in spring.
This result actually makes a lot of sense. In spring, males sing to attract and court females, so they are rewarded by the feeling they get from the female’s response, not from the act of singing itself. But in fall, males are not attracting females. So why do they sing in fall? Because it feels good.
You can't go wrong
when you're singing a song
Sing it loud, sing it strong
It feels good when you sing a song
But why does singing feel good? At least some of the reason, it seems, is opioids. Not quite what Sesame Street had in mind, but hey.
Despite their reputation for being one of the world’s oldest drugs, many opioids are naturally occurring neuropeptides (brain chemicals). They are involved in pain relief and euphoria, commonly combined in the phenomenon of runner’s high. Could opioids be involved in the feel-good sensation created by singing? Maybe.
Cindi, Sharon and Lauren suspect that singing in fall causes male starlings to release opioids in their little brains, which makes singing more rewarding and makes them want to sing more. But how do we know how much opioid an animal has in its brain? Hmmm… Opioids cause analgesia (pain relief). Therefore, if singing a lot in fall releases more opioids, then birds that sing a lot in fall should be more pain-tolerant, right?
The researchers let male starlings sing and counted how many songs they produced for 20 minutes. Then they dipped their foot in uncomfortably warm water and timed how long it took for the bird to pull its toes out. Fall males that sang more took longer to pull their feet out of the birdy foot-spa than did the males that sang less.
Interestingly, if you give starlings a drug to enhance opioids, they leave their feet in the foot-spa longer than if you give them a drug to block opioids. So it seems that singing in fall increases pain tolerance in the same way that opioids do, likely because the act of singing in fall causes the brain to release its own opioids. (Although it is also possible that birds that produce more opioids feel like singing more).
And what about singing in spring? When Cindi, Sharon and Lauren repeated the study with spring starlings, these birds did not get pain relief from singing. Again, they are probably rewarded by their interactions with females and not the act of singing.
So if you ever find yourself in pain, just
Sing
Sing a song
Make it simple
To last your whole life long
Don't worry that it's not good enough
For anyone else to hear
Sing
Sing a song
La la la la la la la la la la la
La la la la la la la
Want to know more? Check these out:
1. Riters LV, & Stevenson SA (2012). Reward and vocal production: song-associated place preference in songbirds. Physiology & Behavior, 106 (2), 87-94 PMID: 22285212
3. Riters LV, Schroeder MB, Auger CJ, Eens M, Pinxten R, & Ball GF (2005). Evidence for opioid involvement in the regulation of song production in male European starlings (Sturnus vulgaris). Behavioral neuroscience, 119 (1), 245-55 PMID: 15727529
4. Kelm CA, Forbes-Lorman RM, Auger CJ, & Riters LV (2011). Mu-opioid receptor densities are depleted in regions implicated in agonistic and sexual behavior in male European starlings (Sturnus vulgaris) defending nest sites and courting females. Behavioural brain research, 219 (1), 15-22 PMID: 21147175
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