When you examine any insect up close, you find structures and designs unlike anything you've ever seen. Just pause a moment and dwell on the beautiful intricacy of the veins in the wings of the female Roseate Skimmer at the right. That photo, by the way, was taken by Michael Suttkus in his backyard in Florida.
Part of the beauty of insect construction lies in its practicality. If an insect's behavior is machine-like, so is its form. There's something in insect design reminiscent of the spirit of the master engineers who built early steam engines. Some of us could spend hours admiring all the dials, knobs, levers, cogs, belts, whistles, and bells on a steam- engine's control panel. It's the same way with insect parts. Every insect part gives the impression of having been designed by a creative urge gleefully, artfully, and lustily making up its rules as it went along.
Here are the main parts of an insect:
On the head, the most striking features are eyes, antennae, and mouth parts. Many insect heads, such as those of grasshoppers, looks nearly as if they're composed of several plates of steel and metal rods -- like Darth Vader's face. Interestingly, each face part has a name. There's the gena, the frons, the clypeus, and lots more. If you really dive into insect identification, you'll become familiar with these names, for the same parts appear again and again on many insect species, in many configurations, with many modifications, and their particular sizes and shapes will help you identify your species. Sometimes the parts will look radically different, but you'll know what they are because of their position. Sometimes the parts will be fused with other parts. And sometimes the parts will be absent, or replaced by something else entirely.
Insect eyes come in two types, simple and compound. Simple eyes, also called ocelli, are like tiny, round windows, while compound eyes appear to be made of dozens, or hundreds, of massed-together simple eyes. Most insects have three very small simple eyes and two much larger compound eyes, and this is clearly the case with the periodical cicada (order Homoptera, family Cicadidae) shown at the right. The two big red "eyes" are actually the compound eyes composed of hundreds of simpler eyes. Between the red compound eyes you can see a triangle of three simple eyes.
Antennae come in a bewildering variety of shapes and sizes, from mere stubs, to very large, colorful, feathery ones on some moths. One detail important for identification is that the number of antenna segments is often constant within a group. Scarab beetle antennae, for instance, are 8- to 11-segmented, while those of ladybird beetles are 3- to 6-segmented. The antennae on the yellowjacket pictured here are 12-segmented in females, 13-segmented in males. Here you can see that sometimes counting antenna segments isn't easy. However, in many species it is easy, and it's a good feature to help with identification.
Mouth parts are usually adapted for either chewing or sucking. Elsewhere we speak of the "Big Ten" insect orders. Here is how the Big Ten stack up with regard to whether their species have chewing or sucking mouth parts:
• Diptera (flies, mosquitoes... )
• Hemiptera (true bugs)
• Homoptera (cicadas, aphids... )
• Lepidoptera (butterflies, moths)
• Coleoptera (beetles)
• Dermaptera (earwigs)
• Isoptera (termites)
• Odonata (dragonflies, damselflies)
• Orthoptera (grasshoppers, crickets...)
• *Hymenoptera (ants, wasps... )
*Hymenoptera also has "chewing-sucking" species
We have a special page showing several kinds of insect mouth parts.
Legs are important in insect identification, especially the tarsus part, which more or less corresponds to a jointed foot. As with antenna segments, it's often important to notice how many segments comprise the tarsus. Tarsi on members of the order Odonata (dragonflies and damselflies) consist of 3 segments, while those in the order Isoptera (termites) possess 4 segments, and flies in the order Diptera have 5. At the left this Wood Cockroach (Orthoptera) has 5-jointed tarsi.
Wings are the very books in which the identities of many insect groups are written. Good insect field guides include drawings such as those to the right, showing how the wings' individual veins connect with one another. Each open space framed within the veins is known as a "cell." And each vein and each cell has it own name. In the drawing at the right it's easy to find the difference between the Common House Fly of the genus Musca, or the Little House Fly of the genus Fannia.
Ovipositors are sometimes seen on certain female insects, such as the beetle at the left. The ovipositor is that stiff-looking item protruding from the beetle's rear end. It is used to insert eggs wherever they need to be for hatching. Most fieldguide illustrations show the species without ovipositors, and ovipositors come in a variety of sizes and shapes, so don't let the presence of an ovipositor confuse you when you're trying to identify something.
To get a better feeling right now for insect structure and design, you might want to surf to Iowa State's bug-site called the Insect Image Gallery, where you can see lots of insect types.
Article courtesy of Jim Conrad of Backyard Nature.