What are insects?
Insects are animals. They are also invertebrates. Invertebrates are animals that do not have a bony, internal skeleton or a backbone.
Where do insects live in Illinois?
They are found in every habitat in the state.
How big are insects?
In Illinois, the smallest insects are so small, they are difficult to see with just your eyes. The largest insect in Illinois is the
cecropia moth (Hyalophora cecropia) with a wingspan of about six inches. Some other insects in the world can get over a foot long!
How many kinds of insects are there?
Worldwide, there are nearly 1,000,000 insect species. Approximately 1,000 new species of insects are named each year! Scientists estimate there are four million insect species that have not yet been discovered.
How do insects grow?
All insects start out their life in the egg stage. From here there are several ways insects become adults. Metamorphosis is the change in shape and habits of an insect as it grows into an adult. Insects develop from an egg to an adult in three ways.
No metamorphosis - The insect's size changes as it matures. For example, this is how a silverfish develops. Its life stages are egg, young and adult.
Incomplete metamorphosis - The nymph looks like a small adult, but it has no wings and cannot reproduce. A grasshopper develops this way. Its life stages are egg, nymph and adult.
Complete Metamorphosis - The insect must go through two stages between egg and adult. A butterfly has this type of development. Its life stages are egg, larva, pupa and adult.
Insects often move, breathe and eat differently in each stage of development, helping them to survive changes in food supply, temperature or other harsh conditions.
In most cases, the life cycle takes less than one year.
Taxonomy
According to recent taxonomic work, the Kingdom Animalia contains 35 phyla in the world. In Illinois, 16 of these phyla are represented.
The Phylum Arthropoda contains the arthropods. Arthropods have bilateral symmetry and a segmented body. An exoskeleton composed mainly of chitin makes up the body covering. Compound and simple eyes are present. They have an open circulatory system. They have jointed appendages. Insects, spiders, crustaceans, centipedes, millipedes and ticks are some of the species in this phylum.
Class Insecta contains the insects. Insects differ from other arthropods because they have six legs and three main body parts: head; thorax; and abdomen. They usually have two pairs of wings. Legs and wings are positioned on the thorax. Most insects have one pair of antennae. A few insect species have no antennae.
There are numerous insect orders worldwide. Each of these orders contain various families, genera and species. Here are some insect orders that contain species you may be familiar with.
Order: Odonata -
Dragonflies and
Damselflies
Dragonflies and damselflies have a long body and four long, thin wings. When not being used for flight, the wings are held flat out from the body or above the body. The eyes are very large while the antennae are tiny.
Order: Orthoptera -
Katydids, Grasshoppers and Crickets
The orthopterans include katydids, grasshoppers, crickets, mantids, walkingsticks and cockroaches. Most of these insects have four wings, although some are without wings. The body is long and thin. Mouthparts are for chewing. These insects undergo incomplete metamorphosis. (egg, nymph, adult).
Order: Hemiptera - True Bugs
These insects are long or oval and flattened top to bottom. The mouth is beak-like and the eyes and antennae are well-developed. When not being used for flight, the wings are held closed on the back. The front wings have a hard, thick part in front and a thin part in the rear section. Hemipterans have a life cycle of incomplete metamorphosis.
Order: Hymenoptera -
Bees,
Wasps and Ants
The bees, wasps and ants, are three of the more common species classified in this order. Those hymenopterans with wings have four wings. The hind wings are smaller than the front wings and have a row of hooks on the front edge by which they can attach to the front wing. The wings are thin and clear with few veins. The antennae usually have 10 or more segments and are fairly long. Metamorphosis is complete.
Order: Coleoptera – Beetles
Beetles have a long or oval shape and a hard body. The mouthparts are for chewing. The front pair of wings are hard covers that protect the hind wings when they are not being used for flight. Beetles undergo complete metamorphosis.
Order: Lepidoptera -
Butterflies and
Moths
The lepidopterans are the butterflies, moths and skippers. These insects have four, thin wings. The hind wing is slightly smaller than the forewing. Each wing is mostly or entirely covered with scales. The mouthparts are developed for sucking and usually have a coiled tube. They undergo complete metamorphosis. Lepidopteran larvae are commonly known as caterpillars.
Order: Diptera - Flies and Mosquitoes
The true flies have only two wings. The hind wings are present only as small projections from the body known as halteres. Mouthparts are for piercing and sucking, or cutting and lapping. Adults are terrestrial, but many larvae are aquatic.
Where do insects go in winter?
Winter can be cold and unwelcoming in Illinois. Most food sources for insects are unavailable this time of year. Because they are cold-blooded, they must adapt to survive. Most insects overwinter in one if its life cycle stages.
For example, the
mourning cloak (Nymphalis antiopa) will overwinter as an adult. It will seek shelter in areas that will keep it out of the wind and winter precipitation. It may even make appearances on winter days that are warm enough for flying!
The lifespan of a katydid is about a year. Females usually lay their eggs at the end of summer beneath the soil or in plant stems. Most katydids overwinter in the egg form and hatch in the spring.
The
polyphemus moth (Antheraea polyphemus) overwinters as a pupa. The pupa is formed in a leaf on the ground.
Some insects leave Illinois completely. Insects like the
monarch (Danaus plexippus) migrate to warmer climates to spend the winter. New generations from the original monarchs that went south will begin to populate Illinois in the spring.
Is a
spider an insect?
Spiders are commonly mistaken for insects. Like insects, spiders are arthropods, but they belong to the Class Arachnida. Here are a few differences between spiders and insects.
- Insects have six legs. Spiders have eight.
- Insects have three main body segments. Spiders have two.
- Most insects have wings. Spiders do not have wings.
Insects have compound eyes. Spiders have simple eyes.
Insects have antennae. Spiders don't.
A Few Interesting Insect Facts
- The first insects evolved 300 to 400 million years ago.
- Fossils of butterflies have been found in rocks that are 40 million years old.
- Butterflies taste with their feet!
- The sound of one cicada can be heard more than a quarter of a mile away.
- A fly moves its wings about 330 times each second.
- Some species of dragonflies have been known to fly 43 miles per hour.
- A katydid's ears are located on its front legs near its "knees."
Insects are fascinating creatures and they aren't really hard to find. Start looking for some today!
