You know when you’re out walking with a big horde of your friends and you come to a chasm you can’t step across, so a bunch of you clasp each other’s limbs and make yourselves into a bridge for the rest to walk on?
Eciton army ants do this. And they’re not the only ants that build incredible structures out of their strong, near-weightless bodies. Weaver ants make chains between leaves by holding onto each other’s waists. Fire ants cling together to form rafts and survive flooding.
Ants build these structures democratically, without any leaders. (Or language, or tools.) To learn more about how they do it, scientists went into the forests of Panama.
Led by Chris Reid of the New Jersey Institute of Technology and Matthew Lutz of Princeton University, researchers designed an apparatus to test ants’ bridge-making skills. Eciton hamatum army ants need to build bridges because they’re constantly on the move. They swarm an area of the forest, devour any bugs they find there, and then move on. When they come to a gap in the leaves covering the forest floor, they bridge it to keep the troops moving quickly. Bridges can be just a few ants, or hundreds of them.
The researchers built a device like a miniature, raised roadway with a sharp kink in it. Then they found an army ant trail and put their device right in the middle. They used leaves and sticks that were already covered with the ants’ pheromones to guide the insects onto their device.
If ants walked all the way along this artificial road, they would have to make a wide detour from their original path. But if they built a bridge across the angle, they could continue marching in more of a straight line. A hinge let the scientists widen or narrow the angle the ants would have to navigate.
The army ants successfully shortened their detour by building bridges across the gap. But they didn’t start at the widest part. Instead, they built their bridge at the skinny end of the angle, where it took only a few ant bodies. Then they gradually scooted the bridge toward the wider end, adding ants as they went.
Although the ants bridged the gap handily, they didn’t manage to stretch across the very widest part. Reid and Lutz think this is because of tradeoffs that come with building a footbridge made of soldiers. The more ants are part of a bridge, the fewer are left to carry stuff across it, for example. And the ants maintained a steady ratio of length to width in their bridges, so as bridges got longer, they also needed to get wider.
Once all the troops are across, an ant bridge breaks apart and marches away too. Being part of a living bridge is, presumably, a thankless job for the army ants. But it won’t be long before they get to walk on someone else’s back.
Image and videos: Courtesy of Matthew Lutz, Princeton University, and Chris Reid, University of Sydney.
Reid CR, Lutz MJ, Powell S, Kao AB, Couzin ID, & Garnier S (2015). Army ants dynamically adjust living bridges in response to a cost-benefit trade-off. Proceedings of the National Academy of Sciences of the United States of America PMID: 26598673
They say you can catch more flies with honey than with vinegar. But what about with lazy spiders versus lively ones? When it comes to keeping pests at bay, the personalities of the spiders hunting them are important.
That’s what two behavioral ecologists reported after watching bug dramas play out in a sunny hilltop alfalfa patch. Raphaël Royauté of North Dakota State University and Jonathan Pruitt of the University of Pittsburgh were studying the personalities of wolf spiders (Pardosa milvina). The spiders are common in many types of crop fields, and prey on all kinds of bugs. But individual spiders, like other animals, can have different habits or tendencies. So, the scientists asked, shouldn’t those differences affect which prey the spiders catch?
Yes, it’s important not to anthropomorphize other species or impose our values on them—but sometimes animals are just horrible. For example, kelp gulls. A few decades ago the birds in one part of Argentina realized that for a tasty snack, they could tear flesh from the backs of whales when they came up for air. Eventually the whales learned to protect themselves somewhat from the gulls. But now the gulls have shifted their attention to the whales’ babies, and might be killing them.
Kelp gulls (Larus dominicanus) first got a taste for whale flesh in the 1970s. They began pulling pieces of dried-out skin from the backs of southern right whales (Eubalaena australis) while the whales were relaxing at the water’s surface at Península Valdés, Argentina. This is a calving ground, where mother whales travel to have their young. The pairs stay here for a few months, nursing and swimming together, before they migrate to their feeding grounds.
The gull attacks have escalated over time. Birds now gash the whales over and over with their beaks, opening holes and then gouging deeper into their skin and blubber. They sometimes chase the whales while they swim, waiting for them to come up for air so they can attack again. Read More
Names like “giraffe” and “jerboa” are nice and snappy, but what are you supposed to do when you’re a naturalist trying to name yet another smallish rodent or brownish beetle?
Sometimes all the good options are already taken. At other times, humans have named animals based only on their usefulness to us. Whatever the reason, here are a few species that got a bum deal.
We all have our standards. For humans, it’s the five-second rule. For macaques, it’s “think twice before eating food off a pile of poop.” The monkeys have several ways of keeping their food (sort of) clean. And the most fastidious macaques, it seems, are rewarded with fewer parasites.
On the Japanese island of Koshima, scientists have been studying Japanese macaques (Macaca fuscata) for nearly seven decades. The tiny, forested island is overrun with the monkeys, which live there naturally and sometimes move between the island and the nearby mainland. Back in the 1950s, researchers started feeding the island macaques treats of sweet potatoes and wheat, so they could study the animals more easily. In recent decades, researchers have cut back on the snacks as much as possible without hurting the population. Now they feed the macaques two or three times a week, at a dedicated sandy beach.
Although the Koshima macaques run free, they’re used to seeing humans around. Andrew MacIntosh of Kyoto University’s Primate Research Institute calls the animals “extremely amenable” to experiments. He and graduate student Cécile Sarabian took advantage of this to learn about the monkeys’ hygiene. Japanese macaques sometimes seem to clean their food before eating it—but is that really what they’re doing? And does this habit keep them healthier? Read More
The uncanny valley is a place no one wants to be. Somewhere between machine and human, the theory goes, robots take a dive into creepiness. But roboticists aren’t sure the valley really exists. Now, researchers in California say they have new evidence for this icky zone, and they can even draw a map of it.
Robotics professor Masahiro Mori first proposed the uncanny valley in 1970. The idea feels right—certainly some robots are charming and others, especially androids not quite succeeding at looking human, are a little stomach turning. (An android is a robot designed like a person.) But studies trying to pinpoint this valley have had mixed results. A 2015 review concluded that evidence for the uncanny valley is, at best, ambiguous.
Maya Mathur, a biostatistician at the Stanford University School of Medicine, and David Reichling, a physiologist at the University of California, San Francisco, thought they could do better. Read More
The world’s smallest primate is not an intimidating animal. It has outsize eyes, nibbles on fruit and insects, and would fit in your breast pocket. Yet at least one species has a super-strong grip, which might help humans understand how our own hands evolved.
Among many species of mouse lemur, the largest—not that that’s much of a distinction—is Microcebus murinus, the gray mouse lemur. Like all other lemurs, M. murinus lives wild only in Madagascar. But a captive population lives at the French research institution UMR7179 CNRS/MNHN, where graduate student Pauline Thomas and her colleagues decided to measure the strength of the petite animals’ arms.
Having a strong grip is crucial for an animal like a lemur that lives in the trees. Some lemurs are acrobats that swing and leap between branches; other species, like mouse lemurs, do more subdued clinging. But all of them would be in trouble if they lost a handhold in a high branch. And since the earliest primates—our ancestors as well as the lemurs’—are thought to have lived in trees too, their need to hang on tight may have influenced what our hands look like today.
The researchers studied 62 captive gray mouse lemurs, both males and females. They measured “pull strength,” or how well the animals can hang on to something. As has been done with other species, the researchers studied this by simply letting the lemurs latch on somewhere and then gently pulling them free.
In this case, the lemurs gripped a little iron bar. The bar was mounted to a force plate, which measured how much force the lemurs were exerting. Then a researcher tugged the animals horizontally away from the bar. The experiment was repeated multiple times with each animal to make sure the tiny athletes performed consistently.
Comparing the results to the lemurs’ body measurements, the researchers found that heavier individuals could pull more strongly. Longer forearm bones also made for stronger lemurs. As the animals got older, their grips weakened. And females with more young were stronger, probably because their bodies had been in better condition to begin with. On average, the mouse lemurs could pull over 10 times their own body weight.
This was an impressive performance, compared to some other animals whose pull strength scientists have tested. Mice can pull less than a quarter of their body weight, and rats can pull just 7 percent.
Gripping tree branches and grasping bugs to eat aren’t the only tasks that require a mouse lemur’s hand strength. Mouse lemurs are promiscuous, and during mating the males have to cling to the slightly larger females. Scientists don’t know yet how the gray mouse lemur’s grip strength compares to other primates, though. The diminutive lemurs might only be average.
But if senior author Anthony Herrel had to guess, he thinks mouse lemurs are likely extraordinary.
Mouse lemurs live on especially narrow branches, Herrel explains. “To walk on narrow branches you need to be able to grip really well, as otherwise you will topple sideways.” To get some data, Herrel hopes to compare M. murinus to other lemur species with different lifestyles.
Herrel says the earliest primates may have been adapted for hanging on to narrow branches, just like the mouse lemur does. So further research might provide hints about how all primate hands evolved, as well as whether mouse lemurs are really strength champions. “Our data suggest that, at least, they are quite strong,” he says.
Image: courtesy of Pauline Thomas.
Thomas, P., Pouydebat, E., Brazidec, M., Aujard, F., & Herrel, A. (2015). Determinants of pull strength in captive grey mouse lemurs Journal of Zoology DOI: 10.1111/jzo.12292
Help do some science! Is it your first time visiting Inkfish? Do you read every post? Either way, you can be part of a scientific study without leaving your chair or sniffing a poop stick. I’ve teamed up with researcher Paige Brown Jarreau to create a survey of Inkfish readers. By participating, you’ll be helping me improve Inkfish and contributing Paige’s research on blog readership. You will also get FREE science art from Paige’s Photography for participating, as well as a chance to win a t-shirt and other perks. It should take 10–15 minutes to complete the survey, which you can find here: http://bit.ly/mysciblogreaders. Thank you!!
Don’t let the makeup companies find out. Lady glow-worms are setting an unattainable beauty standard by using bright light to show males how fertile they are. It’s a rare (in the animal world) example of females decorating themselves while their mates choose between them.
The European glow-worm, or Lampyris noctiluca, is a member of the firefly family in which the females do most of the glowing. Males are ordinary-looking beetles with brown wings. Females are much larger and don’t have wings at all—they look more like overgrown larvae. In their adult stage, glow-worms usually live for less than two weeks. They don’t even eat, focusing all their energy on finding a mate. Read More
Never heard of an Omura’s whale? There’s a good reason. Until recently, no one had laid eyes on one in the wild.
Before 2003, the Omura’s whale was thought to be simply a dwarf version of another type of whale. Then Japanese scientists studying the whale’s DNA and bodily characteristics decided it ought to be its own species, and named it after the late cetologist Hideo Omura. Still, all they had to work with were carcasses caught by whalers or washed up on the beach. They gleaned what information they could from the animals’ ear wax and stomach contents, but no one had ever seen Balaenoptera omurai swimming or eating or interacting. Pretty much all scientists knew was that it lived in the western Pacific.
Imagine the surprise, then, of researchers in a boat in the Indian Ocean when they spied some Omura’s whales in the distance. During a survey of marine mammals off Madagascar’s coast, New England Aquarium scientist Salvatore Cerchio and his colleagues saw whales with markings that seemed to match B. omurai. They used biopsy darts to snag tissue samples from 18 of the whales as they swam by. DNA analysis confirmed it: the animals were the elusive Omura’s whales.
Over the next few years, the scientists returned and recorded every detail they could about this population. Since they were the first humans to observe Omura’s whales in nature, everything they learned about the animals was new: Read More
When birds set out for a long journey, they don’t need roads and they certainly don’t need road maps. They learn the route from others or intuit it from their DNA, an urge to point their bodies one way at a certain time of year and stop flying a few thousand miles later. To understand these journeys better, researchers mapped the most efficient routes through the world’s winds. The highways that emerged weren’t the shortest paths—but they did strikingly match the behavior of real bird species.
At the Max Planck Institute for Ornithology in Germany, Bart Kranstauber and his colleagues wondered whether migration routes have evolved to fit wind patterns. If certain routes take more energy to fly, shouldn’t birds be less likely to survive those journeys? And if wind patterns are consistent from year to year, won’t species evolve to follow the easier migratory paths?
The scientists gathered 21 years’ worth of global wind data. Read More