JUNE
1999

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

06-10-99

Insect Legs Are Not Just for Walking

One of the defining characteristics of adult insects is that they have six legs. In some historical scientific circles, insects actually were called hexapods, based on leg number.

Some immature insects don't follow the six-leg scheme of adult insects. 

Some immatures, like fly maggots, don't have any legs. Others, like caterpillars, have more than three pairs of legs. Technically, those caterpillars still have six legs. The things that look like legs are called prolegs, but they function in a similar fashion to legs.

Insect legs come in many sizes and shapes. You can learn a lot about an insect by looking at the way the legs are shaped. For instance, many insect legs are very much like human legs in structure. Both insects and humans have a leg part called a femur. We call it our thigh bone. Below that, in both insect and human legs, is a tibia. We call that our shin bone. The bones making up our feet are called tarsae. The same is true of insects. Our legs and the similar insect legs function to run or walk. Insects like cock roaches, ladybugs and fireflies have legs that function to walk or run.

Legs in insects exhibit many modifications from the basic walking shape. For instance, the front legs of camel crickets look like miniature shovels. The insect uses the front legs to dig its burrow. Dung beetles have front legs that are similar to those of the cave cricket. The dung beetles use forelegs to dig, but also to fashion balls of mammal dung. The dung, or manure, is buried in the ground and is the food for immature dung beetles.

Some insects, like crickets, grasshoppers, katydids and fleas, have hind legs modified for jumping. All of these insects are well-known for their ability to jump when attempting to escape from danger.

The front legs on some insects are designed for grasping. The praying mantid has legs like that. Mantids use their forelegs to catch and hold the insects that become their food. The same is true of other insects that make meals of their cousins. Water striders use their front legs for grasping, as do the predators known as assassin bugs.

Dragonflies and damselflies have legs that function mainly for perching on plants. But these insects use their legs to form a basket, which is used to trap small flying insects when the dragonfly overtakes them in flight.

Insects that live in water have legs shaped as paddles for swimming. Lice have legs that are designed to grasp the hair of their hosts. In fact, many insect legs have devices that allow them to cling to things—claws for hooking into something soft and sticky pads for hard, slick surfaces like glass. Many insects have both claws and sticky pads so they are equipped to walk on or hang on almost any surface.

Insects also use their legs for functions other than locomotion and grasping. Several grasshoppers, crickets and katydids have legs with combs that are used with other legs or wings to produce sound. 

Some butterflies and flies have taste buds in their feet. This allows them to taste any item on which they are standing. For butterflies, they use the information to find a host plant for egg laying. For flies, the information tells them if the item they are standing on is good to eat. If so, they extend their mouthparts and begin to feed.

Other modifications of insect legs are to help camouflage the insect. Some insects that feed on plants have legs that resemble leaves to help them blend into their environment.

Another unusual modification of an insect's legs is found in the honey bee. Honey bees have a pollen basket on their back leg. They collect the pollen from their hair with a comb on a leg and place it in the basket for transport to the hive. So honey bees observed with yellow blobs on their legs are pollen collectors with their pollen baskets filled.

It is apparent that insects use their legs for many different functions other than just locomotion. They have to; after all, they don't have a pair of legs modified into arms as we humans do!

 

Writer: Tom Turpin
Editor: Olivia Maddox