Zombie Birds, Astronaut Fish, and Other Weird Animals Page 2
The mantis shrimp is the only type of animal known to detect another type of polarized light called circular polarized light (CPL), which is produced under the water where linear polarized light is scattered as it heads toward the surface. Chiou found that three species of mantis shrimp have shells that can reflect CPL, which causes them to change color. He suggested that the function of this could be that of a “secret communication channel,” allowing courting individuals to send sexual signals to each other without attracting the attention of predatory squids and octopuses that are unable to perceive the reflections.
In mid-2011, researchers from Penn State University described in Nature Communications how their investigation into the visual mechanisms of the peacock mantis shrimp helped them to invent two-part waveplate technology that could improve CD, DVD, Blu-ray, and holographic technology. And elsewhere, researchers are working to improve the CPL filters used in both ordinary and high-tech medical photography by gaining a better understanding of just how the most incredible eyes in the world operate.
A Mouse in Wolf’s Clothing
NORTHERN GRASSHOPPER MOUSE
(Onychomys leucogaster)
A KEEN HUNTER WITH a penchant for howling at the moon, the northern grasshopper mouse is a true wolf in sheep’s clothing. One of three species in the grasshopper mouse family, this strictly nocturnal, stout-bodied rodent hails from the drier regions of North America between central Canada and northern Mexico, stealing burrows from prairie dogs and kangaroo rats by day and hunting by night.
With 70–90 percent of its diet consisting of animal material, the northern grasshopper mouse is one of the most highly carnivorous rodents in the world, regularly making a meal out of prey as tough as tarantulas, scorpions, and other rodents. They grow to around 5–7 inches long, have clublike tails, and are wrapped in dense, silky coats of warm cinnamon or grey with undersides of white. The northern grasshopper mouse’s coloring may give it a rather sweet appearance, but this mouse was born to kill, with long claws for scratching and grasping onto its prey. And unlike most rodents, it has enlarged jaw muscles for a greater bite force, and its molars are specialized for puncturing and slicing through hard insect carapaces and flesh.
Although primarily wanderers, northern grasshopper mice can maintain unusually large territories of around 6 acres each, and they will defend them aggressively. Researchers suspect this is what has led to their incredible calling behavior. Described in 1929 by biologists Vernon Bailey and Charles Sperry as “a long, fine, shrill whistle given in a high key—a wolf howl in miniature,” and again by Bailey in 1931 as “similar to the hunting call of a timber wolf” the howl of the northern grasshopper mouse is as chilling as it is distinct. Later, in 1966, David Ruffer from Defiance College in Ohio wrote in the Ohio Journal of Science that these extremely vocal rodents appeared to have not one, but four distinct calls:
(1) a squeak call emitted by animals less than four days old and by adults during some fights; (2) a high-pitched, chirping call—ech, ech, ech, ech—was an alarm note given by individuals during an intense fight or when they were being removed from a cage; (3) a high-pitched, piercing call which lasted 0.8 seconds (mean of 183 records); and (4) a call similar to type three, but broken so that it sounded like two shortened type-three calls, one immediately following the other, and lasting 0.9 seconds (mean of 71 records).
Ruffer suggested that the third call was a kind of communication between grasshopper mice of the same species, describing how his captive mice would emit this particular call when placed alone in an enclosure, and the longer they were left there, the less frequent it became. The fourth call, on the other hand, was made only when the captive mouse had been made aware of the presence of another grasshopper mouse of either sex, but was unable to find or make contact with it. Remarkably, occasionally when a northern grasshopper mouse is making either call three or four, it will mimic the posture of a wolf, throwing its little head back to point its nose to the sky and howl.
More recently, the northern grasshopper mouse has gained an unfortunate reputation as a carrier of the plague caused by Yersinia pestis—the bacterium that caused the Black Death, which wiped out 200 million Europeans in the fourteenth century. Over the past few decades Y. pestis has decimated five species of prairie dog across North America. For years, researchers were bewildered that a prairie dog population could be completely obliterated by the plague within months, and when another population moved into the vacant burrows, it too would be wiped out by the same disease. How could the plague persist so strongly after the original, infected colony is already gone?
According to James Holland Jones, associate professor of anthropology at Stanford University and coauthor of a paper published in Proceedings of the Royal Academy of Sciences in mid-2011, the pathogen could be getting into the soil to infect the recolonized prairie dog town. Alternatively, it might be carried by a carnivore such as the northern grasshopper mouse, Jones suggested. Prairie dog families, or coteries, live together in well-defined territories that they know not to venture out of, which should theoretically confine the plague within rigid boundaries. But northern grasshopper mice do not respect the prairie dog territories and appear to carry plague fleas from family to family, spreading the disease further and faster than ever before.
“And now the best man, Roger, will give his toast. Oh, and the caterers would like to apologize for completely underestimating just how much everyone here loves fruitcake. Who would have thought? They also said to tell you that they have a stack of spare fruit platters … Okay, okay, I know it’s not the same, you don’t have to boo me, jeez …”
“Thanks, Mike. Hey don’t egg him, he’s family! Ha, kidding! I’m kidding. I barely know the guy. Anyway … We’ve had some good times, Martin and me. I’ll never forget that prank we pulled on those prairie dogs that one time. Poor bastards. We must have killed off, what, fifty, sixty of them in just a couple of weeks? Martin was so good at it, he’d stroll up to their burrows, all, ‘I have an extremely important announcement to make on behalf of the Small Mammals of America Association, you need to gather everyone in the common room immediately!’ So the prairie dogs packed themselves in real tight and Martin rubbed himself on each of them, like, ‘It’s cool, this is just how grasshopper mice say hello.’ And then he’d get up on the podium, unfurl what was supposed to be his very important announcement before telling them, ‘Oh, wait. Oh. Well this is embarrassing. It says “deliver this announcement to the prairie hogs.” Hogs! I’ve never even heard of prairie hogs before. Anyway, sorry for wasting your time, I’ll see myself out.’ ”
“Oh and then this other time, we’re at the pub and Martin’s super drunk, he’s like, ‘If only we could kill off Kate’s parents so easily.’ Ha! What, too far? Okay, okay, I’m done. I’m sitting! I’m sitting. Hey, who ate my fruitcake?”
Birds Coming for Your Brains …
GREAT TIT
(Parus major)
“I have a question: How come the more brains we eat, the dumber we become? The less capable of holding a conversation? The less interested in laundering our clothes and going to work?”
“Braaaaains …”
“I mean, we used to talk about books, and politics, and now it’s all just …”
“Braaaaains …”
“Exactly! Maybe things aren’t as bad as—”
“Braaaaains …”
“Nope, never mind.”
EXTREME HUNGER MIGHT MAKE figurative monsters of us all, but that’s nothing compared to what happens when a pretty olive and yellow bird called the great tit suffers a particularly lean winter.
Tits are a family of birds known for their ingenious behavior. In the British Isles during the 1940s, when milkmen still delivered their milk in glass bottles to residents’ doorsteps, it was reported that a population of blue tits had figured out how to pry open the aluminum milk caps to get to the fresh layer of cream on the surface. And more recently, bat ecologists Péter Estók and Björn Siemer
from the Max Planck Institute for Ornithology in Germany discovered that great tits (Parus major) in Hungary had secured themselves a similarly unexpected meal source.
Great tits are a species of passerine (perching) bird found all over Europe, the Middle East, central and northern Asia, and some regions of North Africa. They are a large species of tit, at 4.9–5.5 inches in length, with a distinctive black crown, neck, and throat, white cheeks, and subtle olive wings that sit on a lemon-yellow breast.
Having observed a single great tit hunt a tiny species of bat called the common pipistrelle (Pipistrellus pipistrellus) in the Bükk Mountains of northeast Hungary in the winter of 1996, Estók set out ten years later to determine whether this was a one-off event, or something the great tits in the area did regularly. He watched more than fifty Hungarian great tits over two winters, discovering that they had taught each other how to use the waking call of pipistrelles emerging from hibernation to track them down, wrench them from their cave roosts, and crack open their skulls to feed on their brains. After entering the cave the great tits needed no more than fifteen minutes to capture a groggy bat, and in some cases were observed carrying the bats out of the cave to be eaten in nearby trees. Publishing in a 2009 issue of Biology Letters, Estók reported that he and Siemer had identified a case of cultural transmission occurring in these birds, where a specific behavior is learned between individuals and passed on through generations.
As part of their research, Estók and Siemer played a recording of the waking bat calls to the group of great tits they had collected from the wild, finding that the noise attracted around 80 percent of them toward the speakers. This was an odd result, they said, because previous studies of bat calls had seen this same chatter drive birds away. They also tempted the great tits with bacon bits and sunflower seeds at the same time as playing the pipistrelle calls to see which they preferred. They found that the great tits preferred the bacon and seeds, which are similar to their usual diet of berries and insects, suggesting that their zombie-esque behavior was motivated by necessity during unusually harsh winters.
The Sock-Loving Vampire Spider
EVARCHA CULICIVORA
WHILE GREAT TITS ARE only part-time zombies, there’s a species of spider that’s a full-blown vampire.
A little Kenyan jumping spider called Evarcha culicivora, otherwise known as the vampire spider, has been found to have a serious case of bloodlust, feeding off it and fueling its sex life with it. The 0.2-inch-long, black, white, and crimson species was discovered in 2003 by biologist Robert Jackson from the University of Canterbury in New Zealand, who has been studying its peculiar habits ever since. One of his investigations revealed E. culicivora as the only predator that chooses its prey based on what its prey has eaten. Which is where humans come in: The vampire spider’s preferred prey is mosquitoes, and the sooner it can make a meal out of a mosquito that has made a meal out of one of us, the happier E. culicivora is.
Jackson and colleagues tested the ability of these spiders to pick a mosquito that has just fed over a mosquito that hasn’t, plus which option—blood filled or regular—they preferred. Because only female mosquitoes are equipped to siphon out and feed on mammalian blood, the researchers presented the spiders with a number of food options, including male mosquitoes. In 2005, they reported in Proceedings of the National Academy of Sciences that E. culicivora chose the blood-filled female mosquitoes over all other kinds of prey 83 percent of the time, and the spiders could pick their favorite kind of mosquito using either sight or smell with a success rate of 90 percent. Great sight is a rare ability in spiders, as those who live in webs can simply wait for their prey to come to them, using vibrations to detect their whereabouts. Webless jumping spiders, on the other hand, rely on keen senses to actively seek out their meals—and what a good meal blood is, because there’s no preparation required, no energy-hungry process of liquefying with digestive enzymes. It’s ready-made and full of nutrients.
Of course, finding and catching mosquitoes that have just fed but haven’t yet fully digested their meal is no easy feat, and researchers think this difficulty could explain why E. culicivora are more attractive to each other if they smell like blood. “This diet might be more difficult to satisfy, and it’s possible that after eating a blood-carrying mosquito, individuals not only smell good because they smell like the preferred prey, but also because they can show a potential mate that they are capable of finding, and catching, this unusual prey,” says Fiona Cross, an animal behavior postdoctoral fellow from the University of Canterbury, who joined Jackson to investigate the aphrodisiac potential of blood for these spiders.
In 2009, Jackson and Cross tested the mate preference of E. culicivora by wafting the scents of spiders that had either fed on blood-filled mosquitoes, sugar-filled mosquitoes, male (therefore with no blood) mosquitoes, or lake flies. They found that only spiders fed with blood-filled mosquitoes were deemed attractive by both the male and female spiders, suggesting that this was perhaps driven by the assumption that they would pass good hunting skills on to their offspring. “E. culicivora has a very weird connection between diet and attraction to the opposite sex,” Cross marvels. “It appears that it doesn’t simply prefer blood-carrying mosquitoes for nutrition alone. In fact, the more I learn about these spiders the more I realize just how complex they really are. Blood really makes these spiders go quite crazy.”
Unlike most jumping spider species, where the males are more active in the courtship process than the females, with E. culicivora both sexes are actively involved in courtship and mate selection. This means the blood diet is important to both sexes in attracting a mate, and Cross found that whether male or female, if an individual has to switch to a nonblood diet such as midges—known as “lake flies” in Kenya—for even one day, they appear to render themselves less attractive.
The idea of lustful, blood-sucking vampire spiders has probably creeped you out enough already, but this story only gets worse with the discovery in early 2011 that E. culicivora is attracted to our smelly, sweaty socks. If you’re sweating anywhere near these tiny predators they will hunt you down, because what better way to locate blood-filled mosquitoes than to follow the source?
Cross and Jackson tested this attraction by wafting the scent of human socks into test tubes containing E. culicivora. The spiders were free to leave the test tubes at any stage, which helped the researchers to determine their levels of attraction to the sock scent. Publishing in Biology Letters, they described how the spiders were more likely to remain in their test tubes if the scent had come from a sock worn for 12 hours beforehand than from a fresh, unworn sock. Whether male, female, or juvenile, E. culicivora remained 15–30 minutes longer if they smelled the scent of smelly socks. “E. culicivora is often found around buildings occupied by people. It seems that they are used to being around people. We also noticed that E. culicivora is more ‘relaxed’ around us; when we run experiments, they behave a lot more calmly than other species do,” says Cross. “Unfortunately for us, though, some mosquitoes are also found around buildings occupied by people. Perhaps being around people is better for E. culicivora for finding this unusual prey. Perhaps human odor assists the spider in finding blood-carrying mosquitoes in particular. We don’t know this yet, but it begs investigation!”
Now, this story isn’t all bad, because these blood-loving spiders show a preference for the female Anopheles, the mosquito genus that can carry malaria, so researchers in Kenya are investigating the potential of using E. culicivora in the fight against the disease. “E. culicivora may be a weird, and complex, animal, but malaria is an even more complicated beast. There is no single magic bullet out there that can, or will, wipe out malaria,” says Cross. “However … E. culicivora comes from the very part of the world where malaria is so serious. Unlike various other methods used for controlling malaria (for example, baited mosquito traps), E. culicivora freely lives in this habitat. Why not learn more about this weird, and remarkable, little animal?”
Blast. “What is it, Grul?”
“I have your supper ready, sir.”
“What is it?”
“Ants, sir.”
“Damn it, Grul! I told you I can only have blood from now on! Were you even listening to me? Just throw them away.”
“As you wish. Shall I make up your coffin, sir?”
“No, leave me. I’m feeling melancholy.”
“Very well, sir.”
I came to the realization that I was a vampire almost twelve months earlier. I had been visiting the little town of Dawnhold on business when I met a curious gentleman sitting alone in the corner of an old bar with thick velvet curtains that cordoned off a series of intimate rooms with rich, green potted palms and purple tapestries lined with golden wool. The man was inscrutable. He sat staring at the densely decorated rug upon which his table sat, and appeared to be studying the grotesque, snarling tigers woven into the fabric. I approached him with all the courage I had just drunk at the bar with a bloody steak.