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 many little window-like structures called ommatidia. Many
insects have three very small simple eyes, or ocelli, and two much larger compound eyes
composed of ommatidia. This is clearly the case with the periodical cicada at the right.
The two big red "eyes" are compound eyes. Between the red compound eyes you can
see a triangle of three simple eyes. The picture below shows a few of the thousands of
ommatidia on the surface of a horsefly's compound eye:
- 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:
- 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.
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.
Black Field Cricket, Teleogryllus commodus, photo & ID by Bea Laporte of Ontario
- Ovipositors are sometimes seen on certain female insects, such
as the Black Field Cricket shown above. At the cricket's rear end you see three
slender items projecting backwards. The ovipositor is the black one in the middle. Notice
how it's split at the tip. Ovipositors are used to insert eggs wherever they need
to be for hatching -- into the ground, into tree bark, into leaves, or wherever the
particular species happens to leave its eggs. Most fieldguide illustrations show
their 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
- In the above cricket photo, the two hairlike items beside the cricket's ovipositor are cerci
(singular cercus). Many insects and arachnids have cerci. They're mostly used for feeling
what's going on behind the insect, but in some species they may be used for fighting or during copulation.