Smelling Feet or Smelly Feet?

Dorothy Hinshaw Patent​
 Nature’s Animal Ambassador

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     Do your feet sometimes smell rotten?  Do you wish you could toss out your shoes and start with a new pair?  We make jokes about smelly feet, but smell and feet have a very different relationship among some insects.

     Take butterflies.  Have you ever watched a butterfly flit over a plant, gently touch its feet to a leaf, and then fly on to the next leaf?  That butterfly isn’t being picky about where to land.  It’s hunting for the right kind of leaf for laying its eggs.  It’s “smelling” the leaf with its feet!

     Actually, we need to qualify that statement a bit.  Some writers will say the insect is “smelling” the leaf while others may write that it’s “tasting” the leaf.  Smelling and tasting are forms of “chemoreception,” or sensing of chemicals.  Smell usually refers to sensing from a distance while tasting generally means actually touching the nerve cells that sense a chemical.

     We humans have cells in our noses that send messages to our brains about chemicals in the air.  We call that our sense of smell.  We have cells on our tongues that sense chemicals dissolved in liquid in our mouths.  That’s taste.

     That butterfly doesn’t have a nose, and its mouth is a long tube for sucking up nectar from flowers.  Its chemoreceptors are elsewhere, like on its feet, around its mouth, and on its antennae.  Most butterflies lay their eggs on the plants that the hatched caterpillars will eat.  Some species are very specific about what plants their young can feed on.  Take the postman butterfly, which lives in Central and South America.  Its caterpillars can only survive on certain species of passionflower vines.  Other species are poisonous to their offspring.

     The female postman butterfly has dozens of special nerve cells on her feet called “gustatory sensilla.”  Scientists think that when she touches gently down on a leaf, these cells can sense chemicals there that would be poisonous to her caterpillars.  She avoids laying eggs on those leaves.  But when she finds a plant that will nourish her young, she’ll alight and lay her eggs.

     Now take your shoes off and move your feet around on the floor.  The only nerve endings on your feet are ones that sense touch.  But then, you don’t need to be able to smell the ground you walk on.  Imagine how gross it would be if your feet could smell the insides of your socks and shoes—yuck!

In these photographs taken through a microscope, you can see the sensory sensilla (arrow) on the feet of the female butterfly on the right, which the male on the left doesn't have. From PLoS Genet. Jul 2013; 9(7): e1003620.

Above: Postman butterfly feeding Right: Female postman butterfly laying an egg. As you can see from these two photos, the postman butterfly can have a variety of color patterns. From Heliconius.org

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A dog’s nose is 300 times more powerful than a human nose, so it’s no wonder that dogs use their incredibly advanced sense of smell to do some very important jobs. In Super Sniffers, Dorothy Hinshaw Patent explores the various ways specific dogs have put their super sniffing ability to use: from bedbug sniffers to explosive detectors to life-saving allergy detectors . . . and more. This dynamic photo-essay includes first-hand accounts from the people who work closely with these amazing dogs. For more information, click here.

Dorothy Hinshaw Patent  is a member of iNK's Authors on Call and is available for classroom programs through Field Trip Zoom,  a terrific technology that requires only a computer, wifi, and a webcam.  Click here to find out more.

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MLA 8 Citation
Patent, Dorothy Hinshaw. "Smelling Feet or Smelly Feet?" Nonfiction Minute, iNK
     Think Tank, 23 Jan. 2018, www.nonfictionminute.org/the-nonfiction-minute/
     Smelling-Feet-or-Smelly-Feet.