JUNE
1993

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

06-24-93

Here a leg, there a leg...

The number of legs possessed by insects is one characteristic that sets them apart from other animals. It has long been recognized that adult insects have six legs. The ancient Greeks sometimes referred to insects as hexapods — hex meaning six, pod meaning foot.

Other arthropods, creatures with jointed legs, have varying numbers of legs. Spiders, mites and granddaddy long legs, for instance, have eight legs. Lobsters and crayfish also have eight legs, if you count the pinchers. Crabs have ten leg-like appendages. Pillbugs, sometimes called roly-polys or sowbugs, have seven pairs of legs.

Millipedes and centipedes are famous for the number of legs they navigate upon. Centipedes, literally hundred-legged creatures, have one pair of legs on each section of their wormlike bodies. Millipedes have two pairs of legs on most body segments. Most millipedes have more than 30 pairs of legs — not even close to a thousand legs, as the name millipede suggests.

The standard insect leg functions much as do other animal legs, for walking or running. In some insects, such as the preying mantid, the front legs are modified into grasping devices used to catch prey. The dragonfly uses all six of its legs to form a basket to trap insects as it flies along.

The mole cricket’s front legs are fashioned into shovels used to dig. Many water insects’ legs look a bit like paddles useful for swimming.

Grasshoppers and crickets have back legs modified for jumping. These hoppers use the spring in their legs to escape enemies. Fleas also have jumping legs, as anyone who has ever tried to catch a flea knows.

The insect equivalent of feet are frequently modified to allow the insect to cling to a variety of surfaces. Many plant-eating insects have claws that aid in gripping plants. Many also have sticky pads on their feet. That is the reason flies and other insects can walk upside down on the ceiling or on the glass in the window. Lice, including human body lice, have claws that allow the insect to hold onto the hairs of its host.

It is the tiny claws you feel when an insect walks on your arm. Robert Frost, in his poem “The While-Tailed Hornet,” admonishes his readers to let the hornet crawl upon them if they can stand “so many prickly feet at once.” When it comes to hornets, however, most of us are less concerned about the feet than some other part of the insect anatomy — the stinger!

 

Writer: Tom Turpin
Editor: Andrea McCann