Quick guide to the anatomy of an insect
This guide is intended for the less experienced entomologists to identify the key structures in the body of an insect for species identification, using the cards available on the web site.
The insect body is divided into three parts clearly distinguishable, the head, the thorax and the abdomen, each divided into segments.
The head is normally provided with jointed appendages of different nature and function, including antennae, of sensory function, and jaws, with food-related functions.
The thorax is composed of three segments, each carrying a pair of legs, typically composed of five articulated pieces, not always clearly distinguishable.
The second and the third thoracic segments are also provided of wings. The wings may be classic-shaped wings, like the wings of butterflies, or may be transformed.
In beetles the front pair of wings is sclerotized (sheathed wings) and forms a protective hard case called elytra. In flightless beetles, as Cerambyx cerdo, Lucanus cervus, Rosalia alpina and Osmoderma eremita, the hind wings are membranous and during the flight are stretched while the elytra are raised. In other groups, in which the ability to fly is not present, as in Morimus asper, the elytra are fused together and form a continuous shield.
The abdomen is formed by eleven segments in true insects, but only a part of them is generally visible in ventral view. The appendixes are absent or extremely small, sometimes cerci (sensory function) are present in the last segment.
Appendices: accessory structures that can be delegated to different and specialized functions.
Sensory function: a structure has a sensory function if it is able to perceive external stimuli, such as olfactory , tactile or auditory.
Sclerotization: process of production and accumulation of chitin (a particular sugar of complex molecular structure) in various anatomical structures forming the exoskeleton (the outer skeleton). The role of exoskeleton it is primarily of making the body of the insect hard and conferring the function of protection and support.
Segments: functional portions in which the main anatomical structures (head, thorax and abdomen) are divided.