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Outside Magazine September 2001

The Wild File

By Stephanie Gregory

Q: How do woodpeckers avoid brain damage after hitting their heads against trees all day? —Jan Nessett, Somers, Montana

A: "The bottom line," says Walter Bock, a Columbia University professor of evolutionary biology, "is that the force generated when the woodpecker hits the tree does not pass through its braincase." Instead, it travels along the bird's upper jaw—which, like those of other birds, connects below the brain and allows shock to dissipate throughout the entire body as the bird drills for insects or pecks out a nest. Naturally, some of the blow does reverberate back into the cranium, but since the woodpecker brain's surface area is relatively large, the impact is absorbed as a slap, not a punch. And because the avian skull fits tightly around its bird brain—like a bicycle helmet rather than a jar containing a pickled egg (a rough description of the human smart-muscle)—it prevents internal bruising. Every bit of cushioning helps: According to the only relevant study, conducted in 1979 at UCLA's Neuropsychiatric Institute, the acceleration force felt by a common acorn woodpecker measures between 600 and 1,200 g's—enough that its eyeballs would literally pop out on impact if it didn't blink.

Q: I recently noticed that my hiking boots are tight. Have my feet stretched from wearing sandals all summer? —R. W. Mann, Tucson, Arizona

A: Either your feet stretched, your boots shrank, you suffer from high blood pressure, or you laced up after an evening of gorging on salty, fluid-retaining Top Ramen. Throw sandals into the equation and, yup, we bet on the first answer. Here's why: A vast network of muscles, tendons, and ligaments connects the 28 bones in each foot (which, together with the bones in the hands, account for more than half the bones of the human body). After your adolescent growth spurt, the pounding weight of each step gradually stretches these tissues, collapsing your arches and lengthening your feet—up to a size and a half by middle age, says Perry Julien, president of the American Academy of Podiatric Sports Medicine. Flip-flops only exacerbate the problem. The inadequate arch support of all but the sturdiest of sandals (Birkenstocks, sport sandals, etc.) allows feet to fall and stretch even farther. Unless you wear them every day all summer, the damage most likely isn't permanent and your feet will rebound in a couple days. But be forewarned: If you let those foot muscles go flabby, there's almost nothing you can do to tighten them.

Q: Why do campfires hiss and pop? —Rob Shen, Boston, Massachusetts

A: Probably because you're stoking them with wet or sappy wood. A snow- or rain-dampened log, for example, stores water in its cell walls until flames and coals—at temperatures between 1,100 and 2,200 degrees Fahrenheit—heat it to approximately 212 degrees. At that point the water inside boils and turns to steam, causing the log's cell walls to inflate like balloons until the pressure becomes so great that they blow apart. The gas explodes hollow pockets between fibers and escapes in a cacophony of hisses and pops. The wood catches fire only after rising another 900 degrees, which takes forever when you're as drenched as the wood. Often the squealing continues long after the fuel is aflame, as one side of it may be dry and burning while the other, still soggy, is blowing its gaskets. Sap responds to fiery temperatures in much the same way, the moisture seeping and bursting from branches as it struggles to ignite. To avoid the noise and ensure a faster-starting blaze, opt for dry low-sap woods like hickory, maple, and birch. Of course, this isn't always possible while camping, but so what. Think of the clamor as nature's version of the 1812 Overture.

Q: How do insects walk upside down on ceilings, tree branches, and other horizontal surfaces? —Jim Blair, Huntsville, Alabama

A: Insects' amazing adhesive abilities, which defy gravity, earthbound predators, and gusts of wind, have also defied scientists in search of explanations. Some credit electrostatic forces; some, miniature suction cups. But most research points to "thin-layer adherence," a chemical bond formed when two smooth surfaces sandwich a fluid. "It's like taking a drop of water and squeezing it between two microscope slides—you'll have a hell of a time trying to separate them," says Tom Eisner, professor of chemical ecology at Cornell University. Visualize a bug standing on the underside of a leaf. For the adhesion process to work, the insect's feet must conform to the contours of the leaf exactly, which is why flies, beetles, and earwigs have hairy footpads. When the foot presses down, the hairs bend like the bristles on a tiny paintbrush, custom-fitting to any surface. The bug simultaneously secretes an oily substance from pores in its feet. Trapped between a bug and a leaf, the fluid sticks, and sticks well. A blue beetle, which sports 10,000 hairs from each of its six feet, can hold up to 200 times its own weight and stay glued even to an upside-down Teflon pan. Try that, Chris Sharma.

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