Slow and Steady Wins the Race: Some animals’ lifestyles let them get away with weird necks
As a rule, all mammals have the same number of vertebrae in their necks, regardless of their necks’ length. Among other animals, like birds, reptiles and amphibians, there’s a little more variety: the long, slender necks of swans have 22-25 vertebrae, while bullfrogs’ necks have just one. Mammals, though – whether they’re a Kitti’s Hog-nosed Bat (the smallest mammal), a blue whale (the biggest) or anything in between – always have seven.

There appears to be good reason to follow the trend. Too many or too few neck vertebrae are associated with stillbirth, childhood cancer, neuronal problems and misplaced or crushed nerves, muscles and blood vessels in humans and some other mammals. Any change in the vertebrae number is probably selected against to avoid these problems, conserving basic mammal body plans in the process.

Rules are made to be broken, though, and both sloths and manatees have abnormal numbers of neck vertebrae. Two-toed sloths (Choloepus) have five to seven neck vertebrae, three-toed sloths (Bradypus) have eight or nine and manatees (Trichechus) have six.

Neither sloths nor manatees seem to suffer from the problems that other species have when they diverge from the seven-vertebrae template, though, and a team of scientists from Austria and the Netherlands think they know how they animals are getting away with it. [Read more]


From my cold, dead paws: Sneaky kidnappings and daring rescues among baboons

ResearchBlogging.orgFor baboons, running away from home is something a boy is expected to do. Most baboon species rely on young males leaving the social group they’re born into and starting or joining another group to disperse genes and ensure diversity. In one species, though, the hamadryas baboon (Papio hamadryas) of northeast Africa, genetic evidence suggests that it’s the females who are the genetic movers and shakers. How that could be was, for the longest time, a real head-scratcher. The most basic hamdryas social group is made up of one male and a harem of 2-11 females. No one was sure how these females could leave, since the males can be a little clingy, keeping their females close through aggressive, and sometimes violent, herding.

In the late 1960s, biologists suggested that females might move to other groups not by leaving on their own, but when they’re abducted by other males. Researchers had, without seeing the abductions directly, found evidence that females in groups they were studying had been taken and then retrieved by the male from their original group within a matter of days. In the four decades since, though, no one had actually seen an abduction happen in the wild (probably with good reason, since observing and recording abductions in detail would require long-term, simultaneous observations of multiple baboon groups).

That changed in a few years ago, when Mathew Pines from the Filoha Hamadryas Project in Addis Ababa, Ethiopia and Larissa Swedell from Queens College in New York were the first people to witness not just one, but three, attempted baboon-nappings and rescues live and in the fur. The pair recently described these abductions in the journal Primates. [Read more]


Man of Steel: Armor, not weapons, protects harvestmen from certain doom

A lot of people mistake harvestmen for spiders, but there are two big differences between the two orders of arachnids. One, harvestmen do not scare the living shit out of me and I do not need to my girlfriend to kill any that wander into our house. Two, the eight-legged freaks commonly called daddy longlegs are awesome beyond your wildest imagination, whereas spiders are demons from Hell and are not awesome.

Among the 6,400 known species of havestmen, there are females who can give birth without the need for a male to fertilize thier eggs. There are males who mate with multiple females and then guard all the eggs, sometimes from egg-eating females they’ve recently mated with. There are harvestmen who enjoy each other’s company so much that they live together in groups of 70,000+ individuals. Then, there’s the granddaddy of wieners, willies, dongs and johnsons, the 400-million-year-old fossilized harvestman that possesses the world’s first known penis.* [Read more]


Stop, Hey What’s That Sound?: Chimps Know Social Upheaval When they Hear it.

ResearchBlogging.orgThe “Ooooooohhhh!” a human being cries out when they stub their toe might sound a pretty similar to the “Ooooooohhhh!” they cry out at the end of their mating ritual, but they two calls are different. An important part of human-to-human communication is our ability to extract information from context-specific calls and integrate it with other information we already have to make sense of what we’re hearing. It’s how we know, if we’re standing in one room and the TV is on in another, the difference between the scream of a serial killer’s victim in a slasher movie and the scream of a hero going into battle in an action blockbuster. We might not know what kind of movie is on in there, but we can at least identify which end of a blade the screamer might be on.

Katie Slocombe, a lecturer at the University of York’s psychology department, has spent her career tracing the evolution of different aspects of human language. More often than not, she finds herself starting with pants, grunts, hoots and hollers of chimpanzees. Many people find this surprising, Slocombe has said, but they shouldn’t. Finding an evolutionary explanation for any part of human language is difficult. Unlike, say, wrist bones, spoken language hasn’t left any fossil remains behind for us to study. Genetic evidence from our hominid ancestors suggests that we evolved our capacity for complex spoken language in a very short window of time, so it’s likely that the cognitive abilities underlying language emerged farther back in the primate lineage. Hence it makes perfect sense to look to other living primates, apes and monkeys, for clues to language’s origins. [Read more]


Context is King: Squirrels’ bodies react differently to warnings about different predators

One if by land, and two if by sea/And I on the opposite shore will be/Ready to ride and spread the alarm/Through every Middlesex village and farm/For the country folk to be up and to arm.

On April 18, 1775, Paul Revere told three Boston patriots to hang two lanterns in the steeple of the city’s Old North Church. A militia waiting across the Charles River in Charlestown kept an eye out for these signal lanterns and were prepared act appropriately as soon as they saw one or both of the lights stab out at the darkness. The meaning of the two lanterns has been memorized by countless American schoolchildren in the century and a half since Longfellow published “Paul Revere’s Ride.” One lantern told the militia that the British Army would march over Boston Neck and the Great Bridge, and two meant that that the Redcoats would take boats across the river to land near Phips farm.

Many, if not most, birds and mammals that live in groups have their own signals and alarms that alert members of the group to predators and other dangers. An alarm call can mean the difference between life and death for animals who didn’t detect the threat on their own and younger animals who are especially vulnerable to predation. Belding’s ground squirrels take a cue from Revere and use two different alarm calls to warn of two types of danger. Whistle alarm calls signal aerial predators and trill alarm calls signal terrestrial ones. A squirrel needs to react differently to each type of call and to each type of predator. Listeners respond to whistles by entering a burrow or another hiding spot, and adopt a “posting” stance on their hind legs in response to trills.

When young Belding’s squirrels first emerge from their burrows when they’re a month old, they don’t respond appropriately to the two different calls and if they respond at all, they typically just freeze. They pick up on the appropriate behavioral responses very quickly, though, often within five days of coming above ground. Watching the responses of mom, dad and the other squirrels could teach a youngster what they need to know pretty quickly, but Jill Mateo, from the Department of Comparative Human Development at the University of Chicago, wondered if there was also a physiological factor. For many species, the sight, sound or even odor of a predator spurs physiological changes that make individuals better prepared to track predators and the responses of other animals, hide and be still, defend themselves or run/fly/swim like hell. Maybe a squirrel’s body reacts differently to a whistle than it does to a trill – to two lanterns than it does to one, if you will – and helps prime the squirrel for one response or another.

For the first five days after they come aboveground, juvenile ground squirrels show a higher level of cortisol (a steroid hormone released in response to stress) than during the days before emergence or the weeks after. To see if the hormone had some role in ground squirrels learning appropriate anti-predator behavior, Mateo tested how the levels of the hormone changed in response to different alarm and non-alarm calls. She caught pregnant female squirrels at a few sites near the Sierra Nevada Aquatic Research Laboratory (SNARL) at Mammoth Lakes, CA and brought them back to the lab so they could give birth and rear their young. Around the time the babies would normally leave the burrow, Mateo placed them, in pairs, in a large, dark wooden box once per day and played either a recording of ground squirrel whistle alarms, trill alarms, squeals young squirrels use during play or a silent control.

Every time a squirrel heard a recording, Mateo took a blood sample from it. These tests continued until she had one blood sample for each of the four recordings from a squirrel or until the squirrel turned 35 days old (in some cases, she was not able to get complete samples from a squirrel before it reached the age limit or did not have a large enough sample to analyze). After two rounds of tests in 2006 and 2008, Mateo had partial samples from 32 squirrels and complete samples from 17 of those.

Mateo analyzed the samples and, using a squirrel’s cortisol concentration following the silent stimulus as its baseline, looked at the hormone’s percent change in response to the alarm calls and play noises. Because multiple squirrels from several different litters were tested, Mateo averaged the cortisol responses to each recording for each litter.

For all litters, cortisol concentrations were higher following playback of trill alarm calls than after the other recordings. The change in cortisol levels compared to the baseline was only significant in response to the playback of the trill alarm calls. The whistle alarms did not increase cortisol concentrations, but earlier research by Mateo showed that they do elicit bradycardia, a slower than normal heart rate.

So the squirrels do have different physiological responses to the two alarm calls. What relationship do these changes inside the body have with behavior, though, and what do they have to do with air versus ground attacks? Mateo hypothesizes that cortisol might not increase in response to whistles because attacks by avian predators often only last a few seconds and most birds don’t make repeated attacks if their first one is unsuccessful; the attack would be over before circulating cortisol increased. Bradycardia, however, is associated in young squirrels with decreased motor activity and enhanced information processing. If the heart slows in response to whistles, the squirrels can stay still and pay attention in case it needs to make a break for a hiding spot.

On the other hand, the terrestrial predators that squirrels respond to with trills usually spend a significant amount of time either moving around squirrel burrows or waiting near one to attempt an ambush. Increased cortisol makes glucose available as fuel to the squirrels’ bodies for sustained vigilance in posting stances and, if needed, multiple escape attempts.

Both of these physiological reactions increase arousal and attention in a variety of species, so both might also just aid young squirrels in noticing and paying attention to the responses that nearby adults have to the alarm calls, making for a faster association between the alarms and their appropriate responses.

References: Mateo JM (2010). Alarm calls elicit predator-specific physiological responses. Biology letters, 6 (5), 623-5 PMID: 20236965

Mateo JM (1996). Early auditory experience and the ontogeny of alarm-call discrimination in Belding’s ground squirrels (Spermophilus beldingi). Journal of comparative psychology (Washington, D.C. : 1983), 110 (2), 115-24 PMID: 8681525

Image: “Belding’s Ground Squirrel in the Sierra Nevada Mountains, California, USA” by Justin.Johnsen via Wikimedia Commons. Used under a Creative Commons Attribution 3.0 license.


How is a mantis shrimp like a punching bag? The way it takes a hit.

Mantis shrimp are, ounce for ounce, some of the most fearsome predators that you can pull out of the ocean. The marine crustaceans of the order Stomatopoda (neither shrimp nor mantids, they got the name because of their physical resemblance to both) are tiny and unassuming, but can use their front claws to attack with incredible speed and tremendous force. Stomatopods armed with “smasher” claws (there are also those armed with spearing claws) regularly crack open crabs and snails with cudgels that work on the same principal as crossbows: a spring-and-catch mechanism allows potential energy to be built up and stored and then released all at once. When all that power is unleashed, stomatopods can bludgeon prey with 45 mph strikes (the fastest known limb movement in the animal kingdom) and 340 pounds of force.

These war hammers aren’t just for hunting meals, though. Stomatopods use them on each other in territorial disputes, too. Given what these strikes can do, how have mantis shrimp not power-punched each other into extinction?

There’s two parts to the answer. One is the way they hit each other. When sparring over turf, two mantis shrimp will usually exchange a few strikes to each others’ tails as a way of sizing each other up before committing to a full-on and rumble and mutually assured destruction. The second part is where they hit each other. These ritual test blows are made to each other’s telsons, armored tail segments that are strong enough to take the punishment.

To find out just how strong telsons are and how they withstand such force, Sheila Patek from the University of Massachusetts and Jennifer Taylor, from the University of Indiana took a few shots of their own at them. They got some mantis shrimp, let them live out a few final days eating grass shrimp in luxurious plastic cup accommodations and then put them in the freezer until they were dead, but not frozen solid. Then, they superglued the stomatopods to a strip of Plexiglass and dropped stainless steel balls on them.

The pair recorded the impacts with high-speed video cameras and used the data to calculate the tails’ coefficient of restitution, a value representing the elasticity of an object. The basic principle of the measurement is that the amount of elastic energy absorbed by an object can be measured by the loss of momentum of a colliding object suffers, so the figure is expressed as a ratio of and the post- and pre-impact velocities of the striking object. Coefficients of restitution are often used to characterize and regulate products that take their fair share of blows, like automobiles, body armor, sports equipment and even fruits and vegetables.

Patek and Taylor calculated the telson’s coefficient of restitution as 0.56. This is similar to a major league baseball, which has a coefficient of restitution between 0.45 and 0.50 when hit with a bat. The telson dissipated a significant amount of energy, 69%, when it compressed during impact with the steel balls. The incredible loss of energy implies that the telson absorbs impact inelastically, like a heavy punching bag does.

Patek and Taylor also used micro-ComputedTomography (a 3-D imaging method that uses penetrating waves) scans to examine mantis shrimp exoskeletons to see if they could find anything that might explain the telson’s resilience.

They found that the stomatopods’ tails are two times thicker than normal at three ridges, called carinae, that run along the telson. While the center area of the telson crumples inward upon impact, the carinae don’t deform. This provides a balance of stiffness and compliance that helps impact resistance by both absorbing energy and resisting penetration, a strategy human engineers have co-opted for designing armor.

Reference: Taylor JR, & Patek SN (2010). Ritualized fighting and biological armor: the impact mechanics of the mantis shrimp’s telson. The Journal of experimental biology, 213 (Pt 20), 3496-504 PMID: 20889830

Patek, S., Korff, W., & Caldwell, R. (2004). Biomechanics: Deadly strike mechanism of a mantis shrimp Nature, 428 (6985), 819-820 DOI: 10.1038/428819a

Images: Female Odontodactylus Scyllarus by Roy L. Caldwell, UC Berkeley, for the National Science Foundation. Odontodactylus Scyllarus by Flickr user prilfish, used under a Creative Commons license.


Lying moths use the threat of getting eaten to help their sex lives

It’s a love story as old as time itself: boy Asian corn borer moth (Ostrinia furnacalis) meets girl Asian corn borer moth; girl secretes sex pheromones; boy goes through his courtship ritual, a little song-and-dance routine where he rubs his wings against his thorax to produce a soft, whispering sound. It’s a sweet little love song that, it turns out, hides a vicious lie.

In 2009, this romantic tale played out in a lab in Japan so that Ryo Nakano, from the RIKEN Brain Science Institute’s Laboratory for Biolinguistics, could observe the males’ seduction technique. They knew that the buggy love song increased the moths’ mating success somehow, but its function and effect weren’t clear. Nakano and colleagues ran a series of experiments where the ability either to make or detect the mating sounds were removed so they could figure out the secrets of the song.

Nakano and his team silenced several male moths by surgically removing the sound-producing scales located on their forewings and punctured the tympanic membranes of several female moths so that they couldn’t hear males’ calls. Next they observed how deafened versus intact females reacted to male advances, and how frequently mute versus intact males convinced females to get it on with them.

Intact female-intact male, intact female-silent male and intact males-deafened female pairs were let loose in a flight tunnel to do their thing and the courtship behaviors of the males – exposing their genitalia while fanning their wings, raising the wings into position for producing courtship songs, assuming the position for attempted copulation, etc. – were observed until the females either accepted or rejected their advances. That last part is where things get tricky. For each attempt at sex, the male has to bend his abdomen based on the position of the female in order to get a grip on her genitalia with his genital claspers. It’s a difficult little maneuver, and like human males’ “yawn and put the arm around her” move, even the slightest movement of the female can screw it all up.

Females who could hear the males’ songs readily accepted them as partners and pairs of intact moths got busy 98% of the time. In all, 94 of the 96 intact males succeeded in mating with intact females, though only 15% succeeded on the first attempt and the rest kept trying until they either succeeded or, in the case of two unlucky guys, were interrupted by the escape of the female. When either partner was acoustically impaired – deaf or mute – though, the rates of sexual success fell dramatically. The females eventually accepted only 63% of the muted males after several mating attempts. The other 37% couldn’t get things right, even after repeated attempts, before the females wriggled away (results for the deafened female and intact male pairs were similar). The team also observed that, if the initial mating attempt failed, the males who could make noise pumped up the volume of their song during subsequent attempts and that the sound level strongly affected their acceptance by females.

Nakano and his colleagues noted that neither the intact nor muted males gave up easily. The interruption of the males’ mating attempts was almost always the fault of the female trying to get away from her suitor. The variation in the number of mating attempts and mating success among intact and impaired pairs didn’t seem to be a problem of tenacity, but female behavior and Nakano wondered if that’s where the males’ courting sounds worked their magic.

When the team analyzed the female response to courtship calls, they found that the females froze in their tracks during the serenade, making it easier for the males to mount them. Nakano proposed a “predator recognition” hypothesis that assumed the females recognized the males’ song as the sound of predatory bats. Staying still, of course, is a great way to small insects to “drop off” a bat’s sonar and not be recognized as prey, and bat calls do elicit freezing responses in many insects, including moths. Faking a bat call, then, is a great way for a male moth to cause a freeze response and get the girl to lie still long enough for him to score.

To test this whether this sonic date rape drug actually worked, Nakano and colleagues examined, in a separate study, whether female moths of the species Spodoptera litura, which exhibit mating behaviors similar to O. furnacalis, could discriminate between male songs and bat calls. They couldn’t, and simulated bat calls played over a loudspeaker while muted males attempted to mate with them had the same effect as the courtship song of intact males: they stopped moving and the males had a much easier time of “boring their corn.”

References: Nakano, R., Takanashi, T., Skals, N., Surlykke, A., & Ishikawa, Y. (2010). Ultrasonic courtship songs of male Asian corn borer moths assist copulation attempts by making the females motionless Physiological Entomology, 35 (1), 76-81 DOI: 10.1111/j.1365-3032.2009.00712.x

Nakano R, Takanashi T, Skals N, Surlykke A, & Ishikawa Y (2010). To females of a noctuid moth, male courtship songs are nothing more than bat echolocation calls. Biology letters, 6 (5), 582-4 PMID: 20219743

Image: Ostrinia furnacalis, courtesy of the Hannam University Natural History Museum


It’s not lonely at the top, after all: dominant chimps have more parasites

This post was chosen as an Editor's Selection for

It wasn’t more than a few decades ago that stress was seen merely as an unpleasant mental state or a mild irritation. Stanford neurologist Robert Sapolsky recognized early on, though, that it had real, significant impact on one’s health. In a Wired piece from last summer,  “Under Pressure,” Jonah Lehrer relates how Sapolsky first connected the dots between stress and health while studying baboons: “He noticed, for instance, that the males at the bottom of the hierarchy were thinner and more skittish. ‘They just didn’t look very healthy,’ Sapolsky says. ‘That’s when I began thinking about how damn stressful it must be to have no status. You never know when you’re going to get beat up. You never get laid. You have to work a lot harder for food.’”

The sustained social stress that social animals with low status put up with can grind down their bodies and numerous studies have shown the health gap between high and low ranking individuals several species. High ranking greenfinches clear viral infections more quickly than lower ranking ones, high ranking dairy goats have fewer gastrointestinal parasites less dominant ones and high ranking pigs have more white blood cells available to fight off Aujeszky disease than lowlier swine.

This isn’t to say its all fun and games for the animals at the top of the social hierarchy, though. Sure, dominance has its perks. Everyone wants to groom you, no one’s trying to beat you up and you can always get laid, and, therefore, have the best chance of reproductive success, but acquiring and maintaining that dominance is no easy task and often involves frequent aggression. Testosterone is considered the driving physiological factor of aggression – the hormone has a permissive effect, altering bodily functions that heighten pre-existing patterns of aggression – and is frequently associated with social dominance rank (though no study has shown solid, significant correlations among the three). Testosterone might facilitate a climb up the dominance ladder, but it is appropriately costly, and elevated testosterone levels are associated with increased metabolism, production of oxygen radicals and – mirroring the effects that stress has on low ranking animals –suppression of the immune system.

Michael Muehlenbein and David Watts from Indiana University wondered, since testosterone is immunosuppressive, and high testosterone levels are associated with a high dominance rank, if a high rank would also be associated with a higher parasite burden, a common effect of a suppressed immune system. To get a better grip on the links between dominance, testosterone, health and parasitic infection in nonhuman primates, Muehlenbein and Watts collected fecal samples and behavioral data from a community of chimpanzees in Ngogo in Kibale National Park in western Uganda. With 150 members, the Ngogo community is the largest described in the wild and contained 24 adult males and 14 adolescent males when Muehlenbein and Watts did their research.

The pair logged 1,700 hours of observational data to determine the dominance rank of 22 adult males and collected 67 fecal samples from those individuals. They hypothesized that dominance rank would be directly associated with fecal testosterone and cortisol levels (cortisol is a steroid hormone that’s produced by the adrenal gland in response to stress) and intestinal parasite burden. In order analyze the fecal samples for hormone and parasite levels, the researchers had to dehydrate the chimp droppings for two hours in a small portable oven on top of their camp stove before packing them up and shipping them stateside, an activity that likely caused the occasional cortisol spike at camp.

After analysis, Muehlenbein and Watts found that 1) fecal testosterone, but not cortisol, levels were directly associated with dominance rank, 2) both testosterone and cortisol were directly associated with intestinal parasite richness (number of unique species recovered) and 3) dominance rank was directly associated with worm-like helminth, but not single-celled protozoan, parasite richness (possibly because helminth parasites impose greater immunological costs than protozoans). As suspected, higher ranking chimps had higher testosterone levels and greater parasite burden than the lower ranking ones. Heavy is the head that wears the crown, and the gut below is isn’t doing so well, either.

Testosterone’s effect on the immune system is mainly suppressive. It inhibits antibody production and impairs natural killer cell activity. Muehlenbein and Watts think that a testosterone-suppressed system can’t muster the allergic responses needed to clear gastrointestinal infections. They also suggest that it could be the behavioral, and not the physiological, aspects of alpha male status that leads to an increased risk of parasites. A chimp’s daily travels, social network, nutritional status and certain personality factors – like sociability – all impact its susceptibility to disease to varying degrees, and all those factors vary greatly depending on where a chimp sits in the social hierarchy. High-ranking males usually have wider social circles, get around more and have more mating opportunities and, hence, more risk of acquiring directly-transmitted infections.

Reference: Muehlenbein MP, & Watts DP (2010). The costs of dominance: testosterone, cortisol and intestinal parasites in wild male chimpanzees. BioPsychoSocial medicine, 4 (1) PMID: 21143892

Image: “Alpha male chimp and older chimp jump on fig tree” by Wikimedia Commons user Caelio, used under a Creative Commons license.


Deathstalker v. Nightstalker: Bats take down highly venomous prey without a care in the world

There are some 1,400 described species of scorpion in the world, and while only 25 of those have proven they can take down a human being with their venom, many more of them can easily injure and kill smaller creatures. Given that, you’d expect scorpions to be important predators in desert food webs, but you might not expect them to be equally important as prey.

Otonycteris hemprichii

Yes, despite the pincers and the stinger and the venom, plenty of animals – among them, centipedes, tarantulas, lizards, owls,shrews and bats – regularly chow down on scorpions. Hemprich’s long-eared bat (Otonycteris hemprichii, at right), found in deserts in northern Africa, the Middle East and south-central Asia, considers scorpions a major food group, along with beetles, centipedes and spiders. In Israel’s Negev Desert, the proportions of these groups in the bat’s diet changes throughout the year, with scorpion fragments found in only 10% of bat droppings in the early spring and in a whopping 70% in the late summer.

That’s a whole lot of scorpions they’re eating, and while some of those are certainly weakly toxic Large-clawed Scorpions, the bats also prey on the Palestine yellow scorpion (Leiurus quinquestriatus, below). Everything you need to know about L. quinquestriatus can be summed up in its nickname, the deathstalker. These scorpions are considered some of the most dangerous in the world and possess a highly toxic venom that contains a grab bag of neurotoxins. Their sting can cause extreme pain, fever, convulsions, paralysis and death (via heart or respiratory failure), even in humans. These scorpions are also “sit-and-wait predators” that hunt by remaining quiet and still and lashing out at unsuspecting prey that wanders too close.

They certainly sound appetizing, but how do the bats deal with prey that present such a challenge to both detecting and disabling them? Carmi Korine, of Ben-Gurion University of the Negev in Midreshet Ben-Gurion, Israel, and colleagues found that Hemprich’s long-eared bat is what’s known as a gleaner, which means it takes prey from surfaces and not right out of the air, as many bats do. Korine and his team hypothesized that, like gleaning Pallid bats that prey on scorpions in North America, Hemprich’s bat might rely on passive gleaning to find its meals, simply listening for the prey to make noise instead of actively using echolocation to detect it based on its echo signature. The researchers figured that, if that was the way the bats hunted, then they would select prey based on 1) body size (bigger scorpions being easier to detect), and 2) toxicity (less venomous scorpions posing less risk of injury).

The team captured eight O. hemprichii individuals, set them up in a room with a scorpion buffet that included both living and dead Large-clawed Scorpions (Scorpio maurus palmatus), Israeli common scorpions (Buthus occitanus israelis) and, of course, deathstalkers.

When the bats took off to search for food, they spent a few minutes circling the room and dropped down directly onto a scorpion once they noticed it. They only went after the live scorpions, ignoring the dead ones and even walking right over motionless live ones if they missed on their initial divebomb, confirming that they glean passively and rely on prey noises.

Once they landed on a scorpion, the bats immediately started biting the scorpions’ heads. The scorpions did not take this lying down and fought back, stinging the bats on the head and face and, in one case, under the eyelid. The bats made no observable attempts to either avoid or disable the stingers and once they had killed the scorpions they often ate the whole thing, including the stinger and poison gland.

This is how the bats hunted all the scorpions. Contrary to the researchers’ predictions, the bats showed no preference among scorpion species based on either on size or toxicity, diving on their prey immediately after detection without any further inspection and going only on limited acoustic information. In 49% of the test sessions the bats actually went after the more poisonous of the available species (and in 24 direct comparisons, the deathstalker was chosen 50% of the time).

The researchers did not have an explanation for the bats’ indifference to the danger their meals pose, but speculated that either scorpions aren’t able to pierce the bat’s skin, or that the bats have at least a partial tolerance to the venom. Given that the bats regularly ate the stingers and venom glands, it seems more likely that their just tough enough to handle what the deathstalkers can dish out.

For other takes on this study, see Michael Marshall’s post at Zoologger and Zen Faulke’s post at Neuro Dojo .

Reference: Holderied M, Korine C, & Moritz T (2010). Hemprich’s long-eared bat (Otonycteris hemprichii) as a predator of scorpions: whispering echolocation, passive gleaning and prey selection. Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology PMID: 21086132

Images: “Otonycteris hemprichii” by Wikimedia Commons user Charlotte Roemer, used under a Creative Commons license.

“Deathstalker near Tzehelim, Israel” by Wikimedia Commons user Yair Goldstof, used under a Creative Commons license


Acanthaspis petax and the amazing technicolor corpsecoat

Ed Yong recently reposted his fantastic 2008 post on assassin bug camouflage to keep us entertained while he’s away. I covered the same paper on an old incarnation of my blog, and can’t resist joining in on the reposting fun. Kevin Zelnio of Deep Sea News also has a post about it. Remember that scene in Silence of the Lambs where Hannibal Lecter kills one of his guards, cuts the poor bastard’s face off and then wears it as a mask so he can escape in an ambulance? This great (if only for the appearance of Chris Isaak as a SWAT team captain) movie moment, it turns out, is something of a case of art imitating life.

While disguise and camouflage have a long history in the animal world (stick bugs, chameleons, decorator crabs, etc.), the assassin bug Acanthaspis petax, takes things to a Lecter-esque extreme.

The order of insects called Hemiptera is comprised of some 80,000 species, collectively known as true bugs. The order’s defining characteristic the arrangement of the bugs’ mouthparts: the mandibles and maxillae have evolved into a sheathed proboscis capable of piercing tissue and sucking out liquids. Most hemipterans use their proboscises to suck sap from plants, but the assassin bug prefers to stab them into other insects (usually ants) and inject their prey with paralysis-inducing saliva and digestive enzymes in order to break down and suck up bodily fluids.

A few other types of insect do the same thing. So what? Well, Acanthaspis petax one ups its brethren and sticks the corpse of its meal to its back, which secretes fine, sticky threads. There the corpse sits with others like it, forming a coat of bodies that earlier research suggested might protect the bug from predators.

Robert Jackson and Simon Pollard from the University of Canterbury tested this theory by matching the assassin bugs against jumping spiders in a no-holds-barred insect cage match. Three species of jumping spider which – all stalking, vision-guided predators that wouldn’t be able to detect the assassin bug by smell  - were placed in glass cages with either with naked, unmasked, assassin bugs or bugs bug wearing the bodies of its last few meals.Assassin bugs

All three species of spider went after the uncovered bugs about ten times more than the covered ones (even if the bugs were actually dead and preserved decoys the authors used to control variables associated with using live bugs, like motion, behavior, size etc.).

Jackson and Pollard suggest that the cloak of corpses (or skin coat, if you will) successfully deters predators because the bodies break up the assassin bug’s form into something the spiders don’t recognize. They see a mound distinct from the background, but they dont recognize it as prey.

The remaining question is: why ants? Assassin bugs feed on a variety of other insects they encounter, but their camouflage is consistently composed mostly of ant corpses. Jackson and Pollard suggest the possibility that the spiders avoided the cloaked bugs because ants are formidable prey, using chemical defenses and having a nasty tendency to swarm. The assassin bugs, then, might be using ants in particular as disguises because of their tough guy reputation.

Reference: Jackson, R., & Pollard, S. (2007). Bugs with backpacks deter vision-guided predation by jumping spiders Journal of Zoology, 273 (4), 358-363 DOI: 10.1111/j.1469-7998.2007.00335.x