Digestive system
An insect uses its digestive system to extract nutrients and other substances from the food it consumes.Most of this food is ingested in the form of macromolecules and other complex substances like proteins, polysaccharides, fats, and nucleic acids. These macromolecules must be broken down by catabolic reactions into smaller molecules like amino acids and simple sugars before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as digestion.
The main structure of an insect's digestive system is a long enclosed tube called the alimentary canal, which runs lengthwise through the body. The alimentary canal directs food unidirectionally from the mouth to the anus. It has three sections, each of which performs a different process of digestion. In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax, adjacent to the foregut.
The salivary glands (element 30 in numbered diagram) in an insect's mouth produce saliva. The salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium, located behind the hypopharynx. By moving its mouthparts (element 32 in numbered diagram) the insect can mix its food with saliva. The mixture of saliva and food then travels through the salivary tubes into the mouth, where it begins to break down.Some insects, like flies, have extra-oral digestion. Insects using extra-oral digestion expel digestive enzymes onto their food to break it down. This strategy allows insects to extract a significant proportion of the available nutrients from the food source.[18]:31 The gut is where almost all of insects' digestion takes place. It can be divided into the foregut, midgut and hindgut.
Insects are an extremely diverse type of animal. All have an external supporting structure, called an exoskleton and all have bodies that can be divided into three major areas: the head, the thorax and the abdomen.
The head carries the eyes, mouthparts and a pair of sensory antenna. The thorax provides support for three pair of legs and usually two pair of wings. Some insects, such as ants and termites, do not have wings. The abdomen contains most of the insect's digestive system and it reproductive organs.
Parts vary greatly by species, but the grasshopper shown above is somewhat representational. On the pages that follow, you will find additional information on heads, legs and wings.