Animals > Arthropods > Insects

Insects: class Insecta

Everyone has seen insects, but most people have never looked closely at one. The purpose of this lab is to get you to look closely at some insects and learn to recognize some of the features that define a few of the many orders within this amazingly diverse class of animals.

Insect features:

In addition to the typical arthropod features, insects have some distinctive characteristics.

3 main tagmata. Insect bodies are divided into three main parts: head, thorax, and abdomen. The thorax is where all the legs and wings are attached.
Wings and flight. Most insects can fly at some point in the life cycle; flight is thought to be one of the characteristics of the common ancestor of all insects. On the other hand, many insects have long, flightless larval or nymphal stages, so you'll find plenty of insects that lack wings.
Metamorphic development. Like most arthropods, insects must molt in order to grow. As they do so, they often dramatically rearrange their bodies to metamorphose from a larval form to an adult form.

Identifying insect orders:

There is a lot of diversity in the class Insecta. In this lab, you'll get an overview of some of that diversity by learning to identify a few orders of insects. To do that, you'll need to learn to recognize some of the characteristics that distinguish one insect order from another. When you see a new insect, start by looking closely at these things:

Wings. Most kinds of insects have wings at some point in their life cycle. However, different insect orders may have very different wings. Most insects have two pairs of wings, but flies have only one pair. Most wings are thin and functional for flying, but some insects (beetles, for example) have one pair of wings that is hard and doesn't look like wings at all. Finally, insects don't have wings in their larval stages, and some kinds of insects don't have wings at all.
Mouthparts. Insects have compicated mouths, with many parts; hence the term "mouthparts." Different orders of insects have different ways of eating, so they have different kinds of mouthparts.
Antennae. Each insects has a pair of chemosensory antennae on its head, used for sensing chemicals in the air, water, or on solid surfaces. The antennae vary widely, from tiny (e.g., dragonflies) to huge and elaborate (as found in some beetles).

Learn to look at these three things, and you're well on your way to identifying many kinds of insects. The images below are intended to help you learn to recognize these characteristics. Later, on a test, you will be asked to look at some insect specimens, recognize what order they're in, and understand what characteristics identify them as belonging to that order.

Beetles: Order Coleoptera

Tiger beetle, Scotland. Note the wing covers, which are opened slightly to reveal the membranous wings hidden beneath. These wing covers are actually the beetle's forewings, modified to become hard and non-functional for flight. This is typical for beetles, and it often confuses beginners trying to use an identification key to the orders of insects. If you didn't look closely, you might be tempted to think that beetles don't have wings at all. In fact, most beetles can fly, using only their hind wings.

Also note the long antennae and the large chewing mouthparts, typical for beetles.

I think this is a larval form of a predaceous water beetle, photographed in Henry Coe State Park. Beetles go through a complete metamorphosis, so their larval forms look completely different from the adults. Many insect live in water during their larval phase and then live in the air for their adult phase, but the beetle pictured here spends its entire life in the water.

Flies: Order Diptera

I photographed this fly on my back porch during a barbecue.

The order Diptera includes all kinds of flies, as well as some other familiar insects such as mosquitoes. "Diptera" means "two wings." Most insects have two pairs of wings, but dipterans have only one pair of flight wings. Their second pair of wings is tiny, not visible in this picture.

This picture shows a good example of "membranous" wings: they are thin and nearly transparent, with visible veins. Most flying insects have membranous wings, but you'll also see other kinds of wings (for example, in beetles, or Coleoptera).

This fly also posed for me in the backyard (they're so much more patient when they're dead).

Again, note the single pair of wings and the very short antennae -- typical features of the Diptera.

Bees: Order Hymenoptera

I found this tired-looking carpenter bee resting on a sock in my bedroom.

There are some flies (Diptera) that look like bees (Hymenoptera), but with careful observation they're not hard to tell apart. Bees have two pairs of wings, but you'll often have to look very closely to tell that they do. Also, bees typically have much longer antennae than flies do.

Termites: Order Isoptera

Termites (Isoptera) look a little like ants (Hymenoptera), but they lack the small waist (between the abdomen and thorax). Also, the Isoptera are named for having two pairs of wings that are the same size.

I won't quiz you on this order; we don't have any specimens in lab.

Butterflies & Moths: Order Lepidoptera

I photographed this butterfly in a nature reserve in Holland.

Like most insects, Lepidoptera have two pairs of wings, clearly visible in this photo. The wings are covered with minute scales, making them more opaque than the wings of a fly. You'll be able to see these scales clearly if you look at the wings of a butterfly under the dissecting microscope. The wings of Lepidoptera are also considered to be thin and membranous, like a dipteran; they only look different because of the scales.

This butterfly is feeding on nectar from a flower. Note the long "tongue" extending down into the flower. One of the identifying characteristics of this order is "mouthparts a coiled tube." When this butterfly isn't feeding, this long tube will be coiled into a tight spiral.

This grass skipper butterfly turned up in my backyard. You can clearly see the fuzziness of the wings; under a dissecting microscope, you would be able to tell that the wings are covered with tiny scales. This is one of the key characteristics of the lepidoptera. Also note the little bulbs on the ends of the antennae; this feature helps distinguish butterflies from moths (shown below).

This is a California Oak Moth. Notice that this moth has antennae that are very different from the butterflies shown above.

Katydids & Grasshoppers: Order Orthoptera

I found this katydid in my backyard.

It's in the order Orthoptera, along with grasshoppers and crickets.

Take a closer look at this insect's head. There are a number of small appendages, like little legs, surrounding the mouth. These insects eat leaves, and so they have chewing mouthparts for biting and handling small bits of food.

You can also see the spiracles on the side of the abdomen. As you may recall from lecture, these are the openings into the insect's tracheal system, allowing air movement for gas exchange.

I think this is a California Rose-Winged Grasshopper; I photographed it in Henry Coe state Park.

I unearthed this Jerusalem cricket in my backyard. These fearsome-looking insects typically feast on decaying organic material, but with their massive jaws, they are capable of killing and eating other insects.

Dragonfly: Order Odonata

Snakefly: Order Neuroptera

I encountered this one in the Utah desert. It's called a snakefly, but it's not a real fly (order Diptera). Instead, it's in the Neuroptera, along with lacewings. Why? For one thing, snakeflies have two pairs of wings.

It's not obvious at first that this insect has two pairs of wings, but take a close look at the anterior end of the wings; the forewing sits on top of the hindwing. Also look closely at the veins, and you'll see that there are two wings on each side.

You won't be tested on the Neuroptera, but I'm including these pictures to make the point that you need to look closely at insects' wings if you want to identify the insect. In particular, if you're not sure if you're looking at a fly (Diptera, with one pair of wings) or a bee (Hymenoptera, with two pairs), you should count the wings.

More information:

BugGuide, a good reference for identifying insects.

Insecta on the Encyclopedia of Life. Good background on all kinds of organisms.

Insect on Wikipedia, in case you really need to see a movie of a bee defecating.

Insect Mouthparts on Wikipedia.

This page updated November 14, 2011