If we could look closely at our ceilings, we’d see the crisscrossing paths of thousands of tiny footprints, left by flies, ladybugs, and other insects (as well as by spiders).  In fact, the problem for flies and other bugs may not be holding onto the ceiling, but breaking free from it.  Turns out, a fly strolling across a ceiling is a bit like a person walking across a field of wet mud.

How do flies walk upside down, apparently effortlessly? Being tiny certainly helps.  Very-low-mass animals like wall-walking insects and spiders feel less of a pull from gravity.  So it’s easier for a fly than a pig to stick to the ceiling (even Spiderpig needed Homer’s help).

On a rough surface, an insect can use its claws, rappelling up or across like a climber on a rock wall.  But many insects and spiders also rely on special leg or foot pads, often covered with bristly hairs, when they need to climb up surfaces.  Scientists once thought that the rough, bumpy hairs allowed flies to cling to tiny nooks and crannies on even smooth-looking surfaces, including ceilings.  A substance secreted by the hairs helped, adding a bit of adhesion.

But in 2006, scientists at the Max Planck Institute in Germany discovered that the substance secreted by the hairs on a fly’s feet is a sticky glue, tailor-made for striding confidently across the ceiling, upside-down.

The glue-y stuff oozing out of a fly’s footpad hairs is a mixture of oils and sugars.  Researchers say that all insects may secrete the glue, since all 300 wall-climbing insects studied at the Institute left a trail of tiny, sticky footprints on the wall.

The adhesive is strong enough to keep each foot planted on the ceiling, fly standing still.  Walking, however, isn’t trouble-free.  Although the journey across the top of a room may look effortless from our perspective, it’s a struggle for the fly.  The researchers found that flies use at least four different techniques to get a foot unstuck and moving again.

Watching slow-motion tapes of each foot detachment, scientists found that a fly sometimes pushed a foot away from himself, popping the footpad off the surface like a freed suction cup.   Flies also twisted their footpads until they loosened from the wall, or jerked them quickly like a yanked-off band-aid.  Flies also used the handy, built-in claws on their feet to pull a footpad off the ceiling, like a person tugging off a boot.

According to the scientists, the techniques that involved peeling the pad off the ceiling or wall work best, because they require less energy.

Using four of six legs as they crawled across the ceiling also helped the flies make their gravity-defying journeys.  (On the ground, scientists say, flies often use just three legs at a time to move around:  two legs on one side and the middle leg on the other, forming a stable triangle, alternating sides with each step.)

No one’s sure where the myth started, but it has legs (er, wings):    Bumblebee flight is impossible.  According to the principles of aerodynamics, the story went, a big, fuzzy bumblebee, powered only by tiny wings, shouldn’t leave the ground.  A French book from the 1930s, for example, cited calculations that “proved” insects in general shouldn’t be able to fly.  But using mechanically-driven fixed aircraft wings to model the flight of bumblebees and other insects just didn’t work.

The mysteries of insect flight are still being unraveled, but today’s scientists say insects fly “in a sea of vortices,” using the swirling eddies of air created by their beating wings to stay aloft.

Bumblebees beat their wings up to 200 times a second, faster than the nerve impulses to their muscles can fire.  This works because bumblebee wing muscles don’t contract and expand with each electrical signal.  Instead, they continuously vibrate, like a repeatedly plucked guitar string.

When a bumblebee rests, its body temperature drops (or rises) to that of its surroundings. But according to entomologists, the temperature of a bumblebee’s wing muscles must be a toasty 86 degrees F. to lift the bee into the air.  So to fly to the nearest flower cafeteria, a bumblebee must dramatically raise its temperature in all but the hottest weather.

How?  Basking in the sun isn’t usually enough, so the bee will shiver her way to a higher temperature.  By rhythmically contracting and releasing her abdominal muscles (faster and faster as her temperature rises), a bee generates enough warmth to take flight.  The warmer the air temperature, the quicker the lift-off.  On a chilly, 42-degree day, a bumblebee must pump her thorax muscles for a tiring 15 minutes to reach 86 F.

Once in flight, a bumblebee’s muscle temperature remains in a range of about 86 to 111 F.  All of this activity expends enormous amounts of energy, provided by the sugars in flower nectar.  Not surprisingly, scientists have found that bumblebees are especially attracted to warm flowers, floral rooms whose color and shape keeps them heated in the sun.

According to Oxford University research published this month, bumblebee flight really is different from that of dragonflies and other insects.  Using a smoke-filled wind tunnel and cameras snapping 2,000 images a second, researchers found that bumblebee flight is surprisingly inefficient.  For example, a bumblebee’s left and right wings flap independently of each other.  And instead of using the varying air pressure at its wingtips to provide some lift, bumblebees use “brute force” to fly and hover.  Bumblebees, say scientists, are the “tanker trucks” of the flying insect world, using incredible amounts of energy to lumber (charmingly) through the sky.

In fact, bumblebees manage to fly even in places where human beings find it difficult to breathe.  On Earth’s highest peak, Mount Everest, bumblebees have been sighted at more than 18,000 feet up.  Although there’s much less air pressure for tiny wings to beat against, bumblebees power on, hot to the touch even in the frigid cold.

Listening for the echoes of their own rapid-fire, high-pitched calls, bats navigate the night, while snatching tiny insects from the air.  Dolphins (along with many whales and shrews) are also skilled “echolocaters.”  And it turns out that we humans, too, are capable of using a kind of sonar, and getting better with practice.  In fact, in the 1800s, one blind man used a kind of echolocation as he traveled the world, mostly on foot, writing about his adventures in a series of books.

Bats are the experts at traveling — and hunting — by listening.  Like submarines in the murky ocean depths, bats move through a sea of echoes, “picturing” objects in their way.

Bats emit high-pitched sounds through their mouths or noses, using their big, oddly-shaped ears to listen for sound reflections.  A bat may sweep your dark yard with sound at 10 blips a second.  When the sounds echo off an insect, the bat increases the rate, giving it a better sense of the bug’s size and location.  As the bat zeroes in, it chirps faster and faster, up to 200 times a second.

While human beings would lose a sonar throwdown with bats, some sight-impaired people do develop the ability to echolocate.  The simplest form of echolocation is tapping a cane or stick while listening for the echoes.  This gives the walker a sense of the changing terrain, as well as objects along the path.  But some people also use clicking or other sounds, much like bats, to determine the location, size, shape, and composition (hard or soft) of objects around them.

California teenager Ben Underwood, blind since he was a toddler, navigates using a series of fast tongue clicks.  Underwood says he began using clicking as a young child, and can even sink baskets by listening for echoes from the basketball pole and backboard.  One scientist estimated that Ben’s sonar clocks in at about 120 clicks a second.

Daniel Kish, a California psychologist who is also blind, practices and teaches echolocation.  His students have even learned to mountain-bike using the human form of sonar.

The first well-known human practitioner of echolocation was James Holman, born in 1786 with normal vision.  James was only 12 years old when he enlisted in the British navy, rising to lieutenant by his 20s.  Then, after an illness involving severe joint pain, Holman lost his vision at 25.

Holman decided to travel the world, using a walking stick and listening for resounding clicks as he trekked through Europe, Asia, Africa, and South America.  The books he wrote about his sometimes-perilous journeys were bestsellers in the 1800s.  After his death in 1857, the so-called “Blind Traveler” was gradually forgotten.  His story is recounted in the book “A Sense of the World:  How a Blind Man Became History’s Greatest Traveler,” by Jason Roberts.

For more on Holman, listen to an interview with Roberts at www.npr.org/templates/story/story.php?storyId=5675082.  For more on Ben Underwood and Daniel Kish, go to  http://abcnews.go.com/Primetime/story?id=2283048.

Hummingbirds use enormous amounts of energy simply being themselves. When a hummingbird is sitting quietly on a branch, its heart beats a staccato 550 times a minute. When a bird is engaged in aerial acrobatics, its heart can speed up to 1,200 beats a minute. A person whose body burned energy at the rate of a hummingbird would have to eat about 155,000 calories a day. In fast food, that’s the equivalent of about 287 Big Macs.

But hummingbirds prefer nectar to burgers. So instead of hovering at the nearest drive-through window, a hummingbird helicopters alongside a flower.

Just as a helicopter can perform feats that put ordinary planes to shame, so hummingbirds can fly rings around other birds — including upside down and backwards (although not in heels).

Most birds fly by flapping, moving their wings forward and downward with great force. A bird’s flight muscles are specialized chest muscles (pectorals), souped-up versions of human pecs. The average bird’s “upstroke” muscles are weak, weighing only 5 to 10 percent as much as its powerful downstroke muscles. But hummingbirds are built for acrobatics. A hummingbird’s pecs make up nearly a third of its body weight, compared to 15 to 20 percent for other birds. (Imagine a 180-lb. body-builder — with 60-lb. pecs). And a hummingbird’s upstroke muscles are as big and powerful as its downstrokes.

Like a regular bird, a hummingbird flaps his or her wings to fly forward. But a hummingbird’s wings rotate at its flexible shoulders nearly 180 degrees. Meanwhile, the tiny bird’s wings beat about 18 to 80 times a second. (Compare that to a vulture’s once-a-second flap.)

By slanting the angle of its wings and using its powerful chest muscles, a hummingbird can tip up and fly backwards. And by spreading its tail and doing a quick backward somersault, a hummingbird can also fly upside down (a position in which its improved upstroke — now a downstroke — becomes important). Finally, a hummingbird can hover. It does so tilting its body nearly straight up and down, while moving its wings forward and backward in a figure-eight. In addition, like a helicopter, a hummingbird can lift straight up into the air.

Recent studies have revealed that hummingbirds combine a bird’s body with the flying tricks of insects, like the hover-and-dart motions of dragonflies. Researchers used microscopic droplets of olive oil, tiny enough to float and move in air. With a laser lighting the droplets, the researchers used an ultra-fast camera to capture the air patterns left in a hovering hummingbird’s wake.

Insects have nearly flat wings, and use a figure-eight wing pattern that creates nearly equal lift during downstrokes and upstrokes. Bird wings are more like human arms than insect wings. And a hummingbird is no match for an insect, since about 75 percent of its weight support, according to the researchers, comes from the downstroke. But other birds’ in-flight weight support comes almost 100 percent from the downstroke. The 25 percent lift on the upstroke gives hummingbirds their insect-like hovering advantage.

Sniff sniff sniff. You can actually see a dog’s nose hard at work, picking up a scent wafting through the air, following the invisible trail a rabbit left in the yard, or investigating your pants leg for evidence of a secret meeting with a cat.

No one knows for sure how much more scent-sensitive dogs are than humans: A thousand times? Ten thousand? But what is known is that a dog’s nose has many more odor receptors, and an olfactory (smell) center that takes up much more room in the brain.

Human beings have about 5 million odor receptors, while dogs, depending on the breed, may have more than 220 million. The small human nose devotes only a postage stamp-sized area to odor receptors. The average dog nose has a mucous-y scent receptor area which, if spread out, would cover a Kleenex tissue. A dog’s nose—moist on the outside, as well as the inside—acts as a magnet to scent molecules in the air and on the ground.

Sniffing—a string of quick inhales and exhales—helps a dog rapidly identify a scent. Each deliberate sniff widens the dog’s nostrils, allowing him to pull in more scent-laden air. According to researchers, a sniff also temporarily straightens the dog’s nasal cavity, allowing odor molecules to proceed directly to receptors deeper in the nose. The contact between molecules and receptors generates nerve impulses, which travel along the olfactory nerves to the brain’s huge smell center. Presto: Scent decoded.

(Meanwhile, Jacobson’s organ, a special chamber above the roof of a dog’s mouth, has its own scent receptors. These transmit nerve impulses to the brain’s hypothalamus, an area associated with social and mating behavior.)

The average dog’s ability to detect a few scent molecules in a trillion others has created a whole industry built on canine noses. Dogs sniff for hidden drugs in cars and planes, follow the trails of hikers missing in the woods, and find the remains of people in the rubble left behind by earthquakes and bombings. Now, scientists are testing the ability of dogs to detect the distinctive smell markers of various cancers.

So far, it seems that dogs are good at detecting melanoma, the deadliest skin cancer. Dogs have also been trained to detect the waste products of lung and breast cancer cells, simply by sniffing a patient’s breath. And some dogs can identify people with bladder or prostate cancer, by picking up on odors in urine. Dogs trained to detect certain cancers, scientists say, might someday help screen whole villages of people in remote areas without easy access to lab tests.

A dog’s sensitivity to scents can even be used to calm her down, in a kind of canine aromatherapy. Researchers in Northern Ireland found that dogs riding in a car filled with the odor of lavender spent more time sitting quietly, less time racing from window to window and yapping in the driver’s ear.

To watch a dog’s nose at work, visit www.sciencentral.com/articles/view.php3?article_id=218391249&cat=3_3.

Unfortunately, many insects don’t survive the freezing cold of winter. Others, however, have come up with clever schemes to hang on until spring.

For example, cluster flies sometimes hide out in the nooks and crannies of a warm house or barn over the winter, venturing out to fly around only on milder winter afternoons.

Mosquitoes, like bears, hibernate through the winter cold. Adult mosquitoes look for dark, damp, hiding places–like your basement–to spend their winter vacation. In spring, the females slowly become active, flying around looking for food (fresh blood). Once they’ve had their blood meal, they’re ready to lay eggs, and hatch a new crop to plague us during the summer.

Some mosquito species do things differently. In summer they lay their eggs. The adults die off. But all through fall and winter the eggs lie still, actually freezing when the weather turns nasty. When the warm rains of spring finally come pelting down, the eggs thaw and hatch.

Some water-dwelling insects burrow into lake and river bottoms for the winter, and some beetles hibernate in tree bark. Certain honeybees cram together into a ball, using their wing muscles to generate heat and keep the temperature above freezing in their hive.

Other insects harden themselves to the cold by changing their body chemistry. For example, certain caterpillars in the far north produce a substance similar to car antifreeze, and can survive even when the temperature drops below -100 F. Like birds, some insects migrate in the fall, escaping the cold for warmer places. Locusts are migrators. So are some species of butterflies, moths, dragonflies, ants, termites, bees, wasps, and ladybugs.

The monarch butterfly, the beautiful orange-and-black insect seen in North America in the summer, is one of the most famous migrators. For many years scientists knew that the butterflies took off for the south in cool weather, but no one knew where they spent the winter.

An entomologist named Fred Urquhart spent more than 40 years trying to solve the mystery of migrating monarchs. Urquhart devised a way to tag individual butterflies by attaching lightweight adhesive strips to their wings. He convinced hundreds of people to help him look for the butterflies on their flights. Finally, he was able to narrow the search for their winter resort to the Sierra Madre Mountains in central Mexico.

In January of 1975, when snow covered the summer homes of the monarchs, one of Urquhart’s friends hiked into a 20-acre area of the mountains, and was flabbergasted by what he saw. More than 1,000 trees were covered from top to bottom with a living carpet of monarch butterflies, half-asleep. There were so many butterflies piled onto the trees that limbs sometimes broke under their weight. The mystery of the missing monarchs was solved.

Domestic cats evolved to do much of their hunting at night. Nowadays, that may mean locating the bowl of cat chow in a dark kitchen (and your cat could as easily do that by smell). But in a power failure, while you are still groping for candles, your cat might be strolling through the living room–without crashing into the coffee table.

In your eyes or your cat’s, the pupil reacts to changing light by changing size. The pupil gets bigger to let more light in, tinier in bright sunlight. Behind the pupil, a rubbery membrane called the lens focuses the light as it passes through. Continuing on through the eye’s inner chamber, the light strikes a screen called the retina. The retina’s nerve cells, called rods and cones, send signals to the brain through the optic nerve, and the brain registers an image.

The cat eye difference? Cats have a special layer of cells at the back of their retinas, called the tapetum lucidum (Latin for “bright carpet”). This shiny layer of cells, acting like a mirror, reflects light back to the retina’s cells.

So in near darkness, a cat’s eyes collect what light there is and give the retina a second chance to absorb every photon. And domestic cats aren’t the only ones with this light-enhancing device. Big cats like tigers and lions, woodland deer, ocean-dwelling whales and even your family dog all come equipped with the “bright carpet” feature.

Cats can’t see in absolute darkness, however. Shut up in a windowless, pitch-black room, a cat finds its cautious way by sniffing everything around it and listening carefully. Most importantly, a cat makes use of its two dozen or so long whiskers to get a feel for the room, as they brush against unseen objects in the dark.

Because a cat’s eyes are well-suited to dimness, you might guess that in bright sunlight, a cat might find it difficult to see–like a person emerging into sunlight, eyes dilated from an eye exam.

When our human eyes are behaving normally, the pupils react to bright light by shrinking down to two tiny holes. Then, if we also begin to close our eyelids against the glare, we soon cut off all light from entering the shrunk-down pupils.

But cat-eye pupils are vertical slits, which simply get narrower in bright light. The neat trick: Cats can lower or raise their eyelids to hide more or less of the slit, just like a window shade. This gives a cat more precise control than nearly any other animal over the amount of light entering his eyes.

Scientists estimate that cats can see clearly in one-sixth the amount of light we humans would need. How would a scene that is dark to you appear to your cat? To find out, visit the website www.lam.mus.ca.us/cats/C10a.

High above the ground, electrical and telephone poles and their connecting wires must seem made for birds, like artificial trees with limbs that stretch on forever. Sometimes a hundred birds will be stretched out along a wire, in a kind of high-tension convention.

How come a bird on a wire doesn’t get shocked? When the bird perches on a live wire, her body becomes charged–for the moment, it’s at the same voltage as the wire. But no current flows into her body. A body is a poor conductor compared to copper wire, so there’s no reason for electrons to take a detour through the bird. More importantly, electrons current flow from a region of high voltage to one of low voltage. The drifting current, in effect, ignores the bird.

But if a bird (or a power line worker) accidentally touches an electrical “ground” while in contact with the high-voltage wire, she completes an electrical circuit. A ground is a region of approximately zero voltage. The earth, and anything touching it that can conduct current, is the ground.

Like water flowing over a dam into a river, current surges through the bird (or person’s) body on its way into the ground. Severe injury or death by electrocution is the result.

That’s why a squirrel can run across an electrical line, but sadly die when its foot makes contact with the (grounded) transformer on the pole at wire’s end.

It’s also why drivers and passengers are warned to stay inside the car if it runs into a downed power line. Touching the ground with your foot would complete the circuit: Electrons would flow from the wire, into the car, and through you on their way into the earth. (Inside the car you are usually protected by the car’s four rubber tires, which act as insulators between car and ground.)

Likewise, birds can get in trouble with power lines if wing or wrist bones–or wet feathers–connect bare wires and grounds.

Raptors (birds of prey) are especially likely to be killed by power lines, particularly in the western U.S. In wide-open plains and deserts, power poles are often the only high perches available for hunters like Bald and Golden eagles and Great Horned owls, who survey the landscape for prey and take off into rising wind currents.

Such large birds can easily contact two wires or a wire and a transformer with their great wingspread. And raptors can easily brush against a live wire while settling onto a (grounded) pole-top. Thousands are killed by power lines each year.

How to protect big birds? Power lines can be made less dangerous by widening the gap between conducting and ground wires, insulating wires and metal parts, and moving wires farther away from pole tops. And guards can be built around favorite raptor perches.

Scientists agree on where chickens came from: In a sense, human beings invented them, just like they invented cows and pigs and other domesticated animals on Old MacDonald’s Farm.

If chickens were interested in tracing their family trees, they would need to bone up on some DNA research done in Japan. Every chicken that ever lived can trace its ancestors, say researchers, to a particular subspecies of Red Jungle Fowl in Thailand.

The male Red Jungle Fowl looks a lot like a storybook rooster. But the Jungle Fowl isn’t identical to a farm chicken. Unlike chickens, female Red Jungle Fowls have no combs. Another Jungle Fowl peculiarity: After mating season, males replace their bright red and orange ruff with a crop of dull, blackish feathers called “eclipse plumage.”

(To see a Red Jungle Fowl in all its scarlet glory, visit the website www.centralpets.com/pages/critterpages/birds/wild_birds/WBD4315.shtml.)

Scientists think the first domestic chickens were bred from Red Jungle Fowls more than 8,000 years ago in the region now divided into Thailand and Vietnam. People bred chickens first for cockfighting contests, later for eggs and meat.

So the first official “chicken” pecked its way out of an egg laid by a bird that was not-quite-a-chicken. Depending on how you look at it, the egg–or the wild chicken–came first.

In creating the domestic chicken–and coming up with some 175 varieties–human beings also created a world where chickens rule the roost: There are more chickens than any other kind of domesticated bird on Earth.

And where did birds come from? Scientists think that a group of egg-laying feathered dinosaurs were probably the ancestors of today’s birds. So if it weren’t for dinosaurs, there wouldn’t be any Jungle Fowl OR chickens.

We’ve solved the riddle of where chickens came from. But there’s still the question of where eggs came from.

Scientists say eggs–handy miniature incubators of life, nutrients already packed inside–evolved more than 1 billion years ago, in the oceans of Earth. When land animals evolved about 250 million years ago, their eggs had a tough covering to retain moisture on dry land. Egg-layers like amphibians, reptiles, and insects flourished. The first “land eggs” pre-dated chickens by about 249,992,000 years.

So “the egg” may be one answer to the old riddle, but here’s another, if a little longer: The chicken came after the bird, the bird came after the dinosaur, the dinosaur came after the egg. And the egg came long after the first single-celled bacteria, the prokaryotes, evolved in the oceans, some 3.5 billion years ago.

There are no bones in an elephant’s trunk, making it as supple as a garden hose. A trunk has more than 40,000 muscles and tendons, and its tip is covered with nerve endings. In addition, there are one or two “fingers” on the tip to grasp small objects. Like a monkey’s tail, a trunk is “prehensile,” and can be wrapped like a rope around an object such as a branch. Unlike a monkey’s trail, an elephant’s trunk can weigh 400 lb. and measure 7 feet long.

All of this makes a trunk flexible (it can hoist a log), strong (the log can weigh more than 300 lb.) and precise (it can pick up a penny lying flat on the floor).

An elephant’s trunk is the Swiss army knife of animal appendages. A trunk-equipped elephant can: Collect gallons of water, and then give itself a quick shower. Snatch the highest, tastiest leaves off a tree. Use its trunk like a periscope to sniff the air for danger. Sprinkle dust on itself to protect from biting flies. Pick up a peanut. Give another elephant’s trunk an affectionate squeeze. Change its nostril size to change the sound of its voice.

An elephant can also wade into a lake, submerge, and use the tip of its trunk as a snorkel as it swims to the other side, breathing easily all the way. Human beings, on the other hand, can only use snorkel tubes that are about a foot long. Snorkel deeper, and the mismatch between air pressure inside lungs and the increasing pressure just outside can make blood vessels swell and rupture.

Elephant lungs are different, according to John West, a University of California scientist who studies lungs. Instead of having a pleural space between lungs and chest wall as we do, elephants have dense sheets of fibery tissue. This tissue allows elephant lungs to withstand pressures that would cause human lungs to collapse. A sign, according to scientists, that elephant ancestors were aquatic creatures.

More evidence: Elephant fetuses start out with funnel-shaped kidney ducts, like freshwater fish and frogs. While the aquatic-style ducts disappear as the unborn elephant grows, their presence early on is a marker of a watery past.

The elephant’s trunk, many scientists think, may have first evolved as a snorkel. But trunks were also useful for gathering sea grasses to eat. The closet living relatives of the elephant may be sea cows, like manatees.

The land-dwelling ancestors of today’s elephants emerged from their aquatic origins about 30 million years ago. Animals born with long trunks had an advantage, since trunks were so useful for gathering food out of reach of many other animals. Eventually, modern elephants with long, strong trunks evolved and flourished.