What Do Dogs Smell?
Don’t let this weird you out, but at least 75 trillion bacteria and other microbes live in you and on you. You may not want to know that 90 percent of the cells in your body are non-human—bacteria, viruses, yeasts, fungi, mites and other micro-critters—but those tiny passengers keep you alive. One top scientist has called your gut “a zoo of bacteria,” with more than 40,000 species, many of which help you digest food. There are even specialized mites that live at the base of your eyelashes and do you a favor by eating what esoteric-science expert Sir Pilthington-Smyth, in his marvelously entertaining book A Beastly Menagerie, calls “the flotsam and jetsam on your skin.”
Indeed, your entire skin is a feeding ground for microscopic creatures. And, because some bacteria produce gas when breaking down old skin cells, your dog can smell what those bacteria have been doing.
Pamelia and I have been doing research on animal senses. When you walk into The Naturalist’s Notebook this year, you will be expected to use all five…I mean all six…no, it might be all 23 of your human senses. (Guess you’re going to have to visit, eh?) Our bloodhound-like noses have led us to fascinating facts about bacteria, eyeballs, tongues, brains, nerve cells and, of course, dogs, the ultimate smelling machines.
Dogs have 44 times as many scent-receptor cells as people do. When Wooster, our Wheaten terrier, steps outside, her nose is bombarded with as many smells as your brain has thoughts in a day. Like other dogs, she ignores many of them. She cares most about smells that she associates with good things (food, affection, play) or bad things (horses, skateboarders, tall men who wear hats).
Tracking dogs pick up extraordinarily minute evidence when following a human’s trail. We homo sapiens constantly shed dog-sniffable skin cells—genetically unique to each of us, and with odor-belching bacteria on board as they flutter through the air and eventually settle on the ground. Not only do our shoes leave aromatic clues, but our every footstep also crushes plant cells and causes the cells to give off a scent that clearly distinguishes our trail from the land around it. The list of smelly evidence we leave on the landscape can make a person quite self-conscious when stomping through the woods.
I’ve been puzzled by Wooster’s frantic sniffing of the snow. She seems to pick up even more intriguing scents after a few inches have fallen, which makes no sense, given that the ground and its odors are covered up. It turns out that at least a couple of factors are at work. One is that by eliminating a lot of smells the snow allows the dog to focus more on certain ones, like the aroma of that fresh squirrel track. Another is that if the snow is airy and powdery, smells do make their way up through it. Avalanche rescue dogs routinely find people buried under five to six feet of snow. In one case in Austria a dog located a skier who was down 24 feet.
I know, I know, you’re still thinking about those 75 trillion microbes that are crawling over every inch of your body. Perhaps I shouldn’t mention that the eyelash mites are arthropods, part of the same phylum of animals as spiders, cockroaches, centipedes, barnacles, crabs and lobsters. But at least they’re small. As the aforementioned Pilkington-Smythe notes, eyelash mites “are in fact only about a third of a millimeter long, which is probably for the best as nothing spoils a pretty face quite like a visible infestation of large armored invertebrates.”
Speaking of Pretty Faces…
You may or may not have watched the red-carpet, fashion-fixated prelude to the Academy Awards broadcast on Sunday night. It brought to mind a delightful section in Bill Bryson’s book At Home in which he traced the evolution of humans’ often bizarre obsession with looking beautiful, from Stone Age clothing through the invention of buttons to the two-and-a-half-foot-tall wigs worn by European women in the 1700s. He wrote that in the late 1700s people in England started festooning themselves with artificial moles, called mouches. And I quote:
“[Mouches] took on shapes, likes stars or crescent moons, which were worn on the face, neck and shoulders. One lady is recorded as sporting a coach and six horses galloping across her cheeks. At the peak of the fashion, people wore a superabundance of mouches until they must have looked rather as if they were covered in flies. Patches were worn by men and women, and were said to reflect one’s political leanings by whether they were worn on the right cheek (Whigs) or left cheek (Tories). Similarly, a heart on the right cheek signaled that the wearer was married, and on the left cheek that he or she was engaged…In the 1780s, just to show that creative ridiculousness really knew no bounds, it became briefly fashionable to wear fake eyebrows made of mouse skin.”
Upcoming Earth Day Movie
Not sure if the stars of this film will end up on the Hollywood red carpet before next year’s Academy Awards, but DisneyNature is releasing Chimpanzee on Earth Day, starring a chimp named Oscar. The footage looks amazing and the very idea that a male chimp would help raise an orphaned baby chimp is startling. If you go to a theater during the opening week of the film (April 20-16), Disney will donate part of your ticket money to the Jane Goodall Institute, another of our favorite organizations. Here’s the trailer:
Quote of the Week
From Natalie Wolchover of Life’s Little Mysteries in an article on bird vision: “If you swapped your eyes for an eagle’s, you could see an ant crawling on the ground from the roof of a 10-story building.”
And That Ant Saw Two Eagles Landing…
Two juvenile bald eagles (no white feathers on their heads yet) just flew in and riled up the 180 or so mallard and black ducks that were floating near our shore. If this was hunting practice, it didn’t go well; the ducks flew off unscathed, and some crows then chased the eagles.
Ah, yes, back to crows. Some of you may have missed seeing this video link in the blog’s “comments” section, sent in by Regina, one of the Notebook’s New York correspondents. Click on it to see a crow engaged in a new winter sport.
Neanderthals In the News
Scientists keep learning more and more about the many human species that preceded homo sapiens. Most went extinct, including the Neanderthals. The widespread belief has been that modern humans helped exterminate Neanderthals (though perhaps there was some interbreeding). Here’s the latest:
Answers to Last Puzzlers
1) The unscrambled words:
a) direans = sardine
b) bronca = carbon
c) suclumu = cumulus
d) maqunut = quantum
2) Bryology is the study of mosses.
1) Unscramble these words from nature, science and art:
2) Fifty-nine years ago next month James Watson and Francis Crick (using the X-ray crystallography data of Rosalind Franklin, who got almost no credit) discovered the double-helix structure of DNA. Which of these statements is NOT true:
a) DNA stands for deoxyribonucleic acid
b) Human DNA contains about 25,000 genes
c) One gene contains about 25,000 types of DNA
d) Plants and animals both have DNA