Insect Morphology and Functions
(hexapod internal anatomy)
Generalized Hexapod Gut Anatomy
The insect insect foregut and hindgut areas are similar in that they both have linings of exoskeleton. These linings are usually shed during molting.
The insect midgut is little more than a single cell layer thick and is the area where absorption of nutrients occurs. The midgut usually has a lining of exoskeleton-like material called the peritrophic membrane. This membrane keeps the food material from damaging the midgut cells. The membrane is normally produced at the junction between the foregut and midgut.
The esophagus (or oesophagus) is merely a thin tube leading to an expanded area, the crop, that holds food until it is ground up in a gizzard-like structure, the proventriculus. In many insects, especially ones feeding on difficult to digest materials, pouches called gastric caeca arise in the front of the midgut. Each gastric caecum often contains protozoa and/or bacteria that aid in digestion.
At the junction of the midgut and hindgut, several long tubes arise which are called Malpighian tubules. These tubules serve as the nitrogenous excretory organs.
Most insects contain special rectal pads that aid in absorbing water from the food bolus. This aids in conserving water and usually produces a dry fecal pellet.
Comparisons of Insect Guts
Each insect has distinctive modifications of the generalized gut. Plant feeding insects often have enlarged gastric caeca where microbes aid in digestion of the cellulose. Below are diagrams of the guts of a springtail (Collembola), a grasshopper (Orthoptera), a caterpillar (Lepidoptera), a ground beetle (Coleoptera) and an antlion (Neuroptera).