JUNE
2005

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

06-23-05

The Insect Underground

To most of us, the word ground brings to mind the surface of the earth. We call the land on which a church, factory or school sits the grounds. We use terms like being on solid ground or being well grounded to describe a steady situation.

Fittingly, something below the earth's surface is frequently described as underground. Thus, some trains, sewers, electrical cables and rivers, because of their location, are referred to as underground.

The term can also be used figuratively to describe something being done by secret means -- for example, a conspiracy to overthrow a government. In the United States , the historical Underground Railroad was used to help fugitive slaves reach free states or Canada .

In general, the idea of the underground is associated with negative things, or at least poorly understood things. Anything that is literally underground is out of sight and, therefore, somewhat shadowy. That is certainly true of those insects that live in or close to the ground.

There are all kinds of small organisms that live in the leaf litter or in the soil itself. This underground life includes round worms, bacteria, fungi, slugs, snails, nematodes, mites, spiders, centipedes, millipedes, sowbugs and insects. In fact, all known orders of insects, except the mayflies, have some members that are underground creatures.

Not only are insects prominent as soil-dwelling creatures, they are the dominant animals on the land. This is primarily because of the soil-inhabiting ants and termites. Either in numbers or in weight, these two social insects rule the earth. The lion is king in name only -- it's the insects that really are in charge!

After the termites and ants, the next most abundant underground group of insects is Collembola. These are very small gray-and-white, soft-bodied creatures that are sometimes called springtails because of a spring-like device that allows them to jump. Many small immature flies also live in the leaf litter. The soil and litter are also home to most cockroaches, earwigs, crickets and silverfish.

Other groups of insects have a few representatives that live in or near the soil. For instance, some beetles. One type is known as ground beetles because they are closely associated with the soil surface. Some mantids, lacewings, booklice, fleas and parasitic wasps can also be found on or under the ground.

There are even a few insects that normally live in water that show up in leaf litter. For instance, an immature damselfly that lives in the damp leaf mold in Hawaii . A few insects spend a portion of their life in the soil. This includes pupae of some moths and butterflies. When the caterpillars of these insects have completed their feeding, they wander from their food plant and form a pupa in the soil. Sometimes, as is the case with the tobacco hornworm, they will spend the winter in the pupal case, well protected by the soil.

Some insects lay their eggs in the soil even though the immatures and adults do not live there. This is the case with most grasshoppers. Many walkingsticks drop their eggs to the leaf litter where they normally spend the winter before hatching.

Several adult insects look to the underground as a winter site for hibernation. Many queen hornets and bumble bees fly from the nest where they were raised to spend the winter in leaf litter. Some ladybugs do the same thing. Only in this case, they crawl under rocks and hibernate as groups.

So what does it take to be a successful insect in the underground? There are four things that are obvious. First, most permanent soil-dwelling insects are small in size. In addition, these creatures tend to be dorsoventrally compressed, which means they are tall and thin, not short and fat. Also, many underground insects do not posses wings, or if they have wings, they are protected by hard covers, as is the case in beetles. Apparently, wings are a liability when moving in the close quarters associated with soil and litter.

Many soil insects also have appendages adapted for such an environment. They may have legs that allow them to run fast or to jump. In addition, some have legs modified for digging. After all, if you live in the underground, digging and tossing dirt can be a good thing!

 

Writer: Tom Turpin
Editor: Olivia Maddox