INSECTS

Insect anatomy

Adult beetle

(taken from Insect Pests in Museums by David Pinniger)

HEAD

Contains brain, mouthparts eyes and antennae. The head functions mainly for food and sensory intake and information processing.

Mouth
Insect mouthparts have evolved for chewing (beetles, caterpillars), piercing-sucking (aphids, bugs), sponging (flies), siphoning (moths), rasping-sucking (thrips), cutting-sponging (biting flies), and chewing-lapping (wasps).

Antenna
Antennae are the insect's feelers. They are sensory organs that can smell, taste, detect sound and air movements. Some insects navigate solely using the antennae. Most insects use them to find and identify food.

Compound eye
Allows the insects to see. Made up of many small lenses arranged in a globe which can give the insect a good field of view. Compound eyes do not produce good definition but they are very sensitive to movement. This is why flies cannot tell that there is glass in a window but can skillfully avoide being swatted by a newspaper.

THORAX

The thorax provides structural support for the legs (three pairs) and, if present, for one or two pairs of wings.

Legs
Insects have six legs. Legs are segmented and vary in shape greatly. Some insects have modified legs which serve special purposes. For example, grasshopper's hind legs are enlarged and very muscular which allow the grasshopper to jump large disances. The legs may be adapted for running, grasping, digging, or swimming.

Wings
Insects usually have 2 pairs of wings. Some insects have no wings at all. Many insects have 1 pair of wings (true flies) others have 2 pairs which behave like 1 pair (wasps). Some insects use all four wings to fast dynamic flight (dragonflies). The front pair of beetles wings are hardened to form a wing case called elytra. When beetles fly, the elytra are raised up revealing a pair of membraneous true wings which unfold from underneath.

ABDOMEN

Contains circulatory, digestive, nervous, respiratory and reproductive systems.

Circulatory system
The internal anatomy of insects is characterized by an open circulatory system; with the exception of a heart and an aorta, there are few blood vessels – insect blood simply flows around inside the body cavity. The blood of the insect is rarely red, usually yellow or greenish. It's predominant function is the transportation of food, waste and hormones, and secondarily provides oxygen and carbon dioxide exchanges for remote body parts not directly served by the trachea.

Digestive system
As with most animals, digestion starts at the mouth, which leads into the alimentary canal, a tube extending from the mouth to the anus. The alimentary canal is divided into three regions; the foregut (stomodaeum), the midgut (mesenteron) and hindgut (proctodaeum).

Nervous system
The insect nervous system transports and processes information received from the sense organs (sight, smell, taste, hearing, and touch).

Respiratory system
Gaseous oxygen is taken into the insects body through spiracles, travels via the trachea throughout the body, into the tracheoles which reach the tissues, is metabolized and leaves the body in the form of carbon dioxide in the opposite sequence although up to a fourth or so of the carbon dioxide may be eliminated through the body wall. The trachea are lined with cuticle, which is thickened in spiral rings for rigidity. The tracheoles are simple cells with thin walls sometimes filled with fluid. This process is usually accomplished by simple diffusion. The spiracles are located on the sides and number from 1 to 10 pairs.

com = commissural trachea; dt = dorsal trachea; lt = main longitudinal trachea; spr = spiracles; st = spiracular trachea; vt = ventral trachea.