June 13, 2006 | David F. Coppedge

Foot Facts: Frogs and Flies Fulfill Feet Feats

How do frogs walk on wet leaves without slipping?  Eric Jaffe in Science News1 describes how they have dual-purpose footwear: a mucous film that holds on by wet adhesion, plus microscopic bumps that protrude above the wet layer to make dry contact.  Though a frog foot doesn’t appear as fancy as that of a gecko, “Now, researchers have evidence that the tree frog’s foot may be surprisingly sophisticated.”
    The frog’s prey has fancy feet, too.  Corey Binns explained on LiveScience how flies can walk on ceilings.  It’s not a simple feat: “Walking upside-down requires a careful balance of adhesion and weight, and specialized trekking tools to combat the constant tug of gravity.”  The fly does it with broad footpads loaded with microscopic hairs that increase the surface area of contact, much like the setae on gecko feet.  (The article includes a stunning electron micrograph of a fly’s foot).  Not only that, the hairs secrete “a glue-like substance made of sugars and oils.”  To get unstuck, the fly simply peels the pad away like a sticky note.  “The combination of the feet hairs’ rounded tips, the oily fluid, and a four-feet-on-the-floor rule help the inverted insect take steps in the right direction,” Binns summarized.

1Eric Jaffe, “Walking on Water: Tree frog’s foot uses dual method to stick,” Science News, Week of June 10, 2006; Vol. 169, No. 23 , p. 356.

We could rhapsodize about the design in a frog leg or fly foot, but you already know the sermon.  Instead, we offer, for your afternoon amusement, a fly joke (there’s already a frog joke on the humor page).  OK.  Three hungry flies buzzed around the kitchen at midnight, discovering to their delight a skillet of bologna.  After gorging themselves on this unexpected feast, they stopped short with alarm, hearing footsteps.  “The human is going to come after us with a swatter if he finds us here,” one shouted.  Stuffed to the gills, they all waddled out to the handle and tried to use it like a runway.  Their flimsy wings could no longer support the added weight, though.  One by one, they launched out, only to collapse in a heap on the floor.  The moral of this story is, “Don’t fly off the handle when you’re full of baloney.”

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