There is an immense number of
insect species on the planet. So many so that no one person can know all of
them. Today there are more than one million insect species that have been
named and described. Some scientists believe that there may be another 15
million yet to be discovered and assigned names. The class Insecta is large
and diverse as well as important ecologically. When compared with other groups,
the number of insect species is much larger than the number of Arachnids
(about 50,000 species) or Crustaceans (about 40,000 species) and represents
more than three quarters of all animal species.
The phylum Arthropoda contains several classes and includes
the insects, spiders, crusteacea, and relatives. These animals have an exoskeleton
and jointed legs.
Characteristics of Insects
The insects body is divided into three regions; the head, throax, and abdomen.
Sometimes it may be difficult to see the division between the abdomen and
thorax. Within each region there are several segments, 3 for the thorax, 11
or 12 for the abdomen, and 6 or 7 for the head. The abdomen contains many
of the important organs including those for digestion, excretion, and reproduction.
The legs and wings, when present, are attched to the thorax. The thorax also
contains the muscles to power the legs and wings. The head has the eyes, antennae,
Insects also have three pairs of jointed legs, one pair of
antennae, compound eyes and up to two pairs of wings. In addition to the compound
eyes, there may be several single-faceted simple eyes. Compound eyes have
several dozen to several thousand independent receptors with their own facets
Many people often identify insects based on their general
appearance. While that usually works well, many insects mimic the appearance
of other insects. This can make identification more difficult when only using
color or general appearance. In order to properly identify insects, we have
learned to look at specific characteristics to avoid confusion. In this example
a robber fly mimics the appearance of a bumble bee for protection.
Most animals recognize, or quickly learn, that bumble bees
have a painful sting. Flies do not. By looking like the bumble bee, the robber
fly is less likely to be bothered by other animals. Note how the 'hairiness'
in similar as is the appearance of the wings. But the fly has only two wings
while the bee has four. The bee has a pinched waist, while that of the fly
is broader. The fly is in the picture to the left.
Here are 2 insects from Kentucky that look alike; the baldfaced
hornet, a fiercely defensive wasp, and a flower fly.
The similarities in coloration are remarkable, but the characteristics
are very different. For example, look at the antennae, the wasp's antennae
are much longer. The flower fly also has a broadly attached waist while the
hornet's is pinched. Although the wasp has four wings and the fly only
two, it is difficult to see in these pictures.
The last pair of look alikes from Kentucky are a paper wasp
and the grape root borer moth.
Not only do they look alike, but the grape root borer moth
acts like the paper wasp, flying during the day (unusual for many moths) and
appearing to search plants for prey. The moth is actually laying eggs, not
hunting for caterpillars to feed its larvae. The size and coloration are remarkably
similar, but other characteristics give away the mimic. The moth has a broadly
attached waist and scaly wings. The wasp has the pinched waist and transparent
To classify insects, that is, to begin grouping similar insects,
we use specific characteristics. By looking at the type of mouthparts an insect
has, the number and characteristics of the wings, and by knowing the type
of metamorphosis it undergoes during development, we can group insects into
orders. Examples of insect orders would be the beetles or the flies.
Common Orders of Insects
Now we will look at some of the common orders of insects that are found in
and around the home and surrounding landscape. All of the photos were taken
in Kentucky.We will group insects by the orders they belong to. You might not
realize it, but you are already familiar with most of these insect orders. For
example, beetles are one group called Coleoptera and flies are another group
called Diptera. All together there are approximately 32 orders of insects, but
we will look at only 10 of them. Rather than trying to memorize the individual
insects within the orders, we will learn the common characteristics they share
within their groups. Here are the groups we will study and the types of insects
within those groups.
Order Orthoptera: Grasshoppers, crickets, cockroaches,
walkingsticks, praying mantids (Most entomologists will split this into several
different orders, but for our Master Gardener training we will group them together)
Order Dermaptera: Earwings
Order Thysanoptera: Thrips
Order Hemiptera: Stink bugs, plant bugs, assassin
Order Homoptera: Cicadas, planthoppers, leafhoppers,
whiteflies, mealybugs, aphids, scales
Order Coleoptera: Beetles
Order Neuroptera: Lacewings, dobsonflies, antlions,
Order Diptera: Flies, mosquitoes, gnats, midges
Order Lepidoptera: Moths and butterflies
Order Hymenoptera: Sawflies, wasps, ants, and
Other Arthropods: Spiders, ticks, mites, millipedes,
centipedes, sowbugs, scorpions
Updated November 2005