How Animals Use Physics To Survive

Mar 29, 2017
Originally published on March 30, 2017 10:36 am

How does a gecko manage to walk on the ceiling? Do cats drink like we do? And what happens when a dog shakes water off its coat? A new book explores how animals use physics in their daily lives.

Here & Now‘s Jeremy Hobson talks with Matin Durrani (@MatinDurrani) and Liz Kalaugher (@LizKalaugher), the authors of “Furry Logic: The Physics of Animal Life.”

Interview Highlights

On writing “Furry Logic”

Liz Kalaugher: “We tried to make it accessible for everybody. There’s so many stories in there — you’ve got the stories of the animals, the stories of the researchers looking at the animals and then you’ve got this story of the physics as well. We really had fun weaving all those stories together.”

On the red-sided garter snake

Matin Durrani: “If you go to Manitoba in Canada, there are some snake pits where thousands of snakes live underground during the winter. They hibernate there because it’s so cold that they bunker down for the winter. Come the spring, they come out and there are these giant balls of snakes on the ground, really cold. Turns out that this was a huge mystery for many, many years, and people really didn’t know what these snakes were doing writhing around above the surface. What they’re trying to do is, the female snakes, they disappear as fast as they can. And the males that come out are trying to steal heat from the other snakes, so they get jumped on by all these other snakes and steal the heat and warm up. It’s called kleptothermy.

“What they do is they coat themselves with sex chemicals, pheromones, so it fools the other snakes to thinking they’re women and they jump on top.”

On squirrels’ defense to rattlesnakes hunting by use of infrared heat

MD: “Snakes and squirrels in California have been fighting for millions of years. But the squirrels are really clever. What they do is they know or they’ve learned that the snakes can detect infrared radiation, so that the blood in their tails gives off this signal. So what the squirrels do is they wave their bushy tails in the air, pump lots of blood into it, and that gives off a lot infrared radiation. And the snakes are fooled and confused and then back off because they see this very unusual signal — not just a tail standing up, but it’s giving off this very unusual infrared radiation, a sort of heat map on the tail. We’re not quite sure what the snakes think, but we reckon they’re confused, and so they back off from the squirrel.”

On how animals know to use physics to their advantage

LK: “That’s a really interesting question. There’s a book about folk physics, and it seems that even humans who don’t know physics formally use physics near enough in that we know if we drop something, we can work out that it will go out in a kind of a parabola to the floor. And that’s good enough. These animals, they don’t know physics in an intellectual way, but they know enough to use them in the same way that a skateboarder would use physics as they fly through the air and be able to land.”

On the physics of a dog shaking off water

MD: “No dog is stupid enough to let evaporation take its course. What a dog does is it shakes itself dry by rotating its backbone back and forth. People have calculated how much energy it saves by doing it rather than letting the water disappear through evaporation. It saves, I think, about a one-five-hundreths of the energy. The interesting thing is that the rules the dog follows to shake itself dry are followed by all hairy animals. There’s some fantastic studies of everything from little rats to big bears. They all follow this same shaking rule.”

LK: “That’s probably that they don’t learn from their parents, although I guess they could learn it by copying their parents. But I would guess that it’s instinctive.”

On the harlequin mantis shrimp, which can break open a crab

LK: “These little shrimp are amazing. They’re not only multi-colored — they’re absolutely beautiful looking — but they have some of the fastest accelerations in nature. To get at the crab meat that they want to eat, they shoot out their elbows on their second pair of, let’s call them legs. And they shoot them out so fast that the amount of force they get through Newton’s second law — that’s related to the acceleration. And because of their muscles, they can’t build up that acceleration just by themselves. They hold their muscles shut and squeeze them very slowly and then release a latch that lets their leg unfold incredibly fast. That creates enough force to smash through the crab. Their problems aren’t over quite then because after they’ve hit a few crabs for a few meals, they could damage themselves. But they have a really clever structure to their shell to protect their own shell from getting cracked.”

On the physics of cats drinking water

MD: “The guy who first studied in-depth how cats drink was a guy at Massachusetts Institute of Technology, Roman Stocker. He was at home one morning watching his cat  over breakfast …  he was watching his cat drink. And it suddenly occurred to him ‘How on earth does this cat drink?’ So, like all good scientists, he went back to his lab, took some high-speed video equipment back home and did some slow motion of the cat drinking. And that’s right. A cat will layer its tongue on the surface of the liquid, it doesn’t enter the liquid. And then it lifts the tip of its tongue very slowly and it forms a column of liquid that it then snaps into its mouth and captures a little bit of liquid every time. And it repeats that several times every second, so it’s quite a quick process. You really have to have these high-speed cameras, and then if you slow down the footage, you can watch it. The fantastic thing is this guy did a really good research paper that was on the cover of the journal Science, which is one of the top journals. Of all the bits of work he did, he said to me that this one had more kudos, had more recognition, than anything he’s ever done. So, studying animals can really be good for your career if you’re a scientist.”

Array

On how geckos walk across a ceiling, and adopting this method for human use

LK: “Geckos are amazing. They use a really quite complicated form of physics called van der Waals forces that you get between molecules if you get the molecules really, really close up. So by putting its feet very close to the ceiling — and it has fleshy folds on its feet and lots of hairs — so by having all these hairs, it gets a huge surface area. Adding up all the very small forces over a lot of area gives the gecko enough force in total that it can walk upside down on the ceiling. If it falls off, it can actually hold its whole body weight with just one foot, and possibly even one toe.

“Some people are actually trying. There’s a material called Geckskin, which copies the folds on the feet. They did manage to get a guy to climb up a glass wall using a pair of gloves using this material. So, that’s pretty clever.”

On the purpose of their book and research

MD: “I think it is partly my job as editor of Physics World, and Liz works with me at IOP Publishing also as a science journalist. We’re always on the lookout for interesting ways to explain what scientists get up to. A lot of people get quite scared by science for whatever reason, or don’t find it interesting. But we always think people love animals, and what a cool way of talking about some exciting physics topics using the guise of animals. And everyone loves cats, everyone loves dogs, there are fish in the book, there are bees and all sorts of animals. Using that as a method of talking about some of the interesting physics that — some of it’s not terribly difficult, it’s fairly straightforward, but fun as well.”

LK: “It’s often that some of the interfaces between different types of science where some of the most interesting stuff happens, so finding out about animals and physics can bring us whole new areas.”

On how humans compare

LK: “One of the things that really interested me was when researchers are looking at animal senses, when animals can sense things that we can’t. There were researchers looking at how turtles use magnetism to navigate, and another researcher looked at how bees use electric fields. And, in both cases, we can’t probably sense those fields. So that’s something I found fascinating.”

Book Excerpt: ‘Furry Logic’

By Matin Durrani and Liz Kalaugher

It’s getting hot in here

In Indiana Jones and the Raiders of the Lost Ark, dashing archaeologist Henry ‘Indiana’ Jones, played by Harrison Ford, faces his worst nightmare. Terrified of snakes, he must brave a secret Egyptian chamber teeming with the reptiles to stop the Ark of the Covenant falling into enemy hands. As in many movies, the scene draws on this animal’s classic image as a creature of both evil and power.

Steven Spielberg, however, had more than symbolism on his mind. After scouring every pet shop in London for snakes, the movie director’s staff had to cut up rubber hoses to make up the numbers. Even some of the ‘snakes’ weren’t snakes but legless lizards, a difference that’s crucial to a biologist, if not to a desperate film crew. Like the slow worm in your compost heap, legless lizards are – as their name suggests – lizards whose legs have shrunk or disappeared.

The actors’ motto ‘never work with children or animals’ could have been coined with snakes in mind. These reptiles bite. They slither. They’re scary. But it’s not just filmmakers who have problems. Biologists studying snakes in the wild have a tricky time too. Snakes are hard to track down, and once a snake has spotted you it’ll slide away or, worse, inject or spray you with venom that could kill if it gets under your skin or into your eyes.

Luckily for our story’s non-phobic hero, Rick Shine from the University of Sydney in Australia, one snake is an exception to this ‘difficult-to-work-with’ rule. Catch it at the right moment and it barely cares if you pick it up. Shine could, if he wanted to, put these reptiles in a car and take them for a ride. Up to a point, as we’ll find out later, he did. In autumn, winter and spring the red-sided garter snake (Thamnophis sirtalis parietalis) hangs out, like Indy’s nemeses in Raiders of the Lost Ark, in huge groups, sometimes tens of thousands strong (there’s a number to make a film director jealous). They won’t be in a secret Egyptian chamber, but in limestone cracks under the frozen soil of the Canadian prairies in the province of Manitoba. For this snake is a record-breaker: it’s the most northerly-living reptile in the western hemisphere.

Living where temperatures plummet to -40˚C and snow coats the ground for eight or nine months a year seems crazy. Reptiles are ectotherms (from the Greek for ‘heat from the outside’) and can’t generate their own body heat by burning food. Instead they rely on outside sources like the Sun, basking in its rays until they’re warm enough to move fast and reproduce. Faced with freezing conditions, red-sided garter snakes huddle together for warmth in their winter hidey-holes and brumate, the snake equivalent of hibernation.

But being in Manitoba brings benefits for the red-sided reptiles, and for those studying them too. For a start, once it arrives, summer is warm, with temperatures touching 30˚C. In April or May the snakes emerge and writhe around on the barren soil in groups hundreds or thousands strong. This sight, which looks like a giant tangle of squirming spaghetti, has intrigued people for years. What are the snakes up to?

With a plot that even Spielberg would be proud of, the mystery of the red-sided garter snake involves cool physics, lots of sex and a soupcon of gender-swapping. Not among Shine and his colleagues, we must stress, but the snakes themselves.

Great garters

Where are our manners? We should get to know this snake before we pry into its sex life. First let’s meet the wider family. Garter snakes live throughout North America, although only those species that dwell where winters are extra-cold brumate. You’ll find these reptiles in woods, forests or grasslands as long as there’s water nearby. About half a metre long, they’re venomous enough to kill small prey but not humans. Favourite snacks include frogs and fish, though the snakes will also feed on earthworms, rodents and small birds.

As for red-sided garter snakes, these reptiles don’t, at first glance, live up to their name; they’re black with cream stripes running the length of their body. Their red sides lie beneath overlapping scales and you can only see them if the snake puffs up its body in annoyance. During Manitoba’s three or four months of summer, the reptiles make the most of the warmth and can stray more than 15km (9 miles) from their dens in search of food.

When the first chill hits the air – in August, no less – the snakes head back to their bunkers. At first they stay down there only at night or when it’s cloudy. Once the daytime temperature drops below freezing, however, the reptiles put themselves under house arrest and snuggle together ready for nine months of cold. Their winter homes lie 6m (20ft) underground, below the frostline. At 10˚C, the ‘indoor’ temperature is no summer’s day but balmier than the -40˚C outside. While they brumate, the snakes barely expend any energy, existing almost in suspended animation. They eat nothing and hardly breathe, getting up only now and then for a drink of water.

All of a slither

Stand by one of the snake pits in or around the village of Narcisse in late spring, the long-awaited sunshine warming your face, and you’ll enjoy one of the most unusual sights in nature. Facing you will be a writhing carpet of mud-caked reptiles that have just emerged from their burrow and are huddling together once more. Stare closely and you’ll notice something even more odd: almost all the snakes are males. At about 45cm (18in) long, they’re some 15cm (6in) shorter than the females.

Undaunted by their smaller size, the male snakes venture outside several weeks before the females. By lying in wait, each hopes to be first to mate. As they slither past one another, the early-risers flick their tongues in search of chemicals called pheromones that the females release through their skin. After nine long months of brumation, sex seems to be the males’ number one aim.

But there’s a hitch. As soon as the females emerge from their lair, most leg it (as far as that’s possible for a snake). Any who are slow off the mark become the centre of attention in a frenzied mating ball of tens or even hundreds of amorous males, each trying to loop his body around her so he’s in the right position to mate. The female finds this stressful and does what she can to escape. With males outnumbering females by 10 or more to one, a male’s chances of reproducing are slim.

The giant tangle of male snakes and these smaller mating balls are freaky enough, but something even weirder’s going on. Look carefully and from time to time you’ll see males give their full attention not to a female, but to another male. We’re not being sexist but some males’ behaviour is most ungentlemanly. Literally. He-snakes pretend to be she-snakes, or ‘she-males’ in the scientific lingo, giving off pheromones to impersonate females. She-males are easy to spot: they’re the same length as other males but, having slithered from underground later, are still coated in mud. Rarely courting ‘other’ females, these transgender snakes crawl around sluggishly instead. Soon the ‘real’ males jump on them.

Harder than identifying the she-males is understanding what they’re up to. If he wants to mate with a female, why does a male pretend to be the same sex as her? This puzzle set biologists scratching their heads. Perhaps becoming a she-male gives a male a reproductive edge so he can steal sperm from other males or avoid attack from larger rivals. But Rick Shine wondered if hanging out in a giant heap isn’t only about reproduction. Could it also be a matter of heat?

Reptiles in the bag

Fortunately biology was on the researchers’ side. You’d think desperate-to-mate garter snakes wouldn’t take kindly to interference. But in late spring, Shine and his colleagues can do what they like with the reptiles – male, she-male or female. Pick them up, measure them, put them in a bag; the snakes don’t have the energy to care, making them almost ludicrously perfect for study. That’s why Shine made a pilgrimage from Australia to snake dens near Narcisse seven years out of eight from 1997 to 2004. ‘Having 10,000 amorous snakes in an area the size of a living room is a snake biologist’s idea of heaven,’ he says.

To find out the she-males’ secrets, Shine and his colleagues simply sat in the grass alongside red-sided garter snakes that were fresh from their winter quarters. Grabbing individual she-males by the tail, the researchers presented them to ‘real’ males to see how they’d react. The males almost always found the she-male a turn-on, pressing their chins on him/her and lining up their bodies. So males definitely fall for the she-males’ pheromone charms. But what’s in it for the she-males?

Time for a more cunning plan. Shine kept one group of she-males at 10˚C, the temperature of their bunker. He warmed another batch of she-males to 28˚C by putting them in cloth bags and placing them on the electrically heated front seats of the team’s four-wheel-drive Yukon hire car. Next the team brought the two groups to a common temperature of 25˚C, heating the cool snakes up on the car seats, while letting the warm group chill off naturally.

Holding each 25˚C she-male by its tail, Shine presented him/her to five different males. As expected, the males flicked their tongues faster and tried to sidle up to the she-male. But their interest didn’t last forever. The guys stopped sniffing around a snake from the ‘warm’ group within about three hours. ‘Cool’ snakes won attention for five hours. The males’ loss of interest revealed that the she-males had stopped gender-swapping and gone back to being simple males, with the ‘warm’ she-males reverting to type faster than the ‘cool’ ones. The conclusion was clear: male red-sided garter snakes become she-males to warm up as fast as they can. By pretending to be a female, a she-male entices other males to press themselves against what they see as a potential mate. Rubbing against his/her warmer rivals, the cold she-male draws heat generated by their muscles into his/her own body. Heat, as we’ll hear later, only ever flows from hot to cold.

Excerpted from FURRY LOGIC by Matin Durrani and Liz Kalaugher. Copyright © 2017 by Matin Durrani and Liz Kalaugher. Excerpted by permission of Bloomsbury Sigma.

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