Some very Basic Insect Anatomy

An introduction to identifying the major parts of an insects body

 

Insects can readily be distinguished from all other arthropods, that is, animals without backbones, by having a body made up of three distinct parts, they also have six legs and usually two pairs of wings.

The three main parts of the body are the head, thorax and abdomen. The thorax and abdomen are in turn divided into a number of segments. The thorax consists of three segments each one of which carries a pair of jointed legs while the last two segments also each have a pair of wings. In many insects the wings may be adapted in various ways such as with many beetles where the fore wings are adapted into a hard protective shell known as the elytra which covers the delicate hind wings which are used for flying. In flies the hind wings have been adapted to form two small paddle-like organs, known as halteres while in other insects the wings may be almost non-existent except for small tubercles on the last two segments. The wings as well as the structure of the veins on the wings are important criteria by which different species are classified.

Here the halteres of the Giant Cranefly (Tipula jocosa) can be clearly seen. Halteres are only found in the order Diptera (flies), they are probably used to control flight which is why flies are able to make such sudden mid-air changes in direction.

This Red-spotted Spittle Bug (Locris arithmetica) which is about to take off, opens its tough fore-wings to free the delicate hind-wings used for flying.

 

An insects abdomen contains the breathing organs, heart, digestive system and sexual organs. There are no legs or wings on the abdomen but it does also have a number of spiracles or breathing holes through which it draws air. The abdomen, being a soft and sensitive part of the body is often protected by a hardened elytra and in many cases may even be difficult to see except from the underside of the body. Some insects, such as certain ant species also have glands in the abdomen through which chemicals can be released for purposes of self-defence.

The antennae, eyes and mouthparts are found on the head. Antennae, which function both as smell and as touch organs differ greatly in length and structure and are an important indicator used in identification of insects and families within insect orders. The antennae are also able to pick up the very faint scent of highly complex chemicals known as pheromones which many insects secrete to attract mates, sometimes over great distances.

Compare the coiled proboscis of the Christmas Butterfly (Princeps demodocus) with that of the rostrum of the Assassin Bug

 

Mouth parts are specifically adapted according to the insects diet and may be suited for chewing or sucking, some have a short strong piercing rostrum for impaling prey while others have a long delicate proboscis designed to reach and suck up nectar deep within flowers. Carnivorous insects often have well developed and strong mouthparts used for both firmly holding as well as chewing up their prey. Some insects, such as assassin bugs are capable of delivering a nasty bite if handled, their sharp rostrums being easily able to pierce human skin.

The fore-legs of the Mole Cricket (Gryllotalpa africana) is greatly enlarged and perfectly adapted for digging.

 

The legs of an insect are jointed consisting of a femur (thigh), Tibia (shank) and tarsus (foot). The tarsus in turn also has several joints and usually ends in either a claw or has pads. Many insects have legs that are especially adapted to catching or holding prey while the legs of others are used for digging, running, swimming and other activities necessary for their survival.

 

 

 

Text and photographs copyright Lambert Smith.

 

© COPYRIGHT Lambert Smith, 2009