EXTERNAL & INTERNAL MORPHOLOGY:WINGS

Insects have evolved many variations of the wing. Wing venation is a commonly used taxonomic character, especially at the family and species level.

Membranous wings are thin and more or less transparent. This type of wings is found

among the Odonata and Neuroptera.

Wing venation

The archedictyon is the name given to a hypothetical scheme of wing venation

proposed for the very first winged insect. It is based on a combination of speculation

and fossil data. Since all winged insects are believed to have evolved from a common

ancestor, the archediction represents the "template" that has been modified (and

streamlined) by natural selection for 200 million years. According to current dogma, the

archedictyon contained 6-8 longitudinal veins. These veins (and their branches) are

named according to a system devised by John Comstock and George Needham -- the

Comstock-Needham System:

Costa (C) – the leading edge of the wing

Subcosta (Sc) – second longitudinal vein (behind the costa), typically

unbranched

Radius (R) – third longitudinal vein, one to five branches reach the wing

margin

Media (M) – fourth longitudinal vein, one to four branches reach the wing

margin

Cubitus (Cu) – fifth longitudinal vein, one to three branches reach the wing

margin

Anal veins (A1, A2, A3) – unbranched veins behind the cubitus

DRAGONFLY

Veins in the wing provide support for the thin, delicate membranous cuticle that

forms the wing itself. Many of the veins have tracheae (tubes that function in

respiration) and provide a passage for haemolymph which is essential for the

functioning of the numerous sense organs found on the wings, including wind

sensitive hairs. Wing venation is also an important morphological characteristic in

taxonomy and can be used to identify many insect groups. Compare the dragonfly

wings to the wings of fruitfly below..

Diptera : Halteres are an extreme modification among the order Diptera (true flies), in

which the hind wings are reduced to mere nubs used for balance and direction during

flight.

In a normal adult fly, the second thoracic segment features a pair of wings, while the

third thoracic segment has a pair of small, balloon-shaped structures called halteres

(see arrow in inset). A modified second wing, the haltere serves as a flight stabilizer.

MOSQUITO WINGS

Elytra (sing. elytron) are the hardened, heavily sclerotized forewings of beetles (Order

Coleoptera) and are modified to protect the hind wings when at rest.

A variation of the elytra is the hemelytra. The forewings of Hemipterans are said to be

hemelytrous because they are hardened throughout the proximal two-thirds

(approximately), while the distal portion is membranous. Unlike elytra, hemelytra

function primarily as flight wings. In both cases, the membranous hind wings (when

present) are used in flight and are folded beneath the forewings when at rest.

Frenulum

The frenulum is a row of bristles along the leading (front) edge of the hind wing of butterflies and moths and also in some Hymenoptera such as bees and wasps. The frenulum connects the hind wing and fore wing and makes the two wings act a single surface during flight. It is therefore more efficient.

The wings of butterflies and moths are covered with scales, and mosquitoes possess scales along

wing veins.

Tegmina (singular Tegmen) is the thickened fore wings of some insects. The tegmina are used to protect the more vulnerable hind wings. The tegmina offer little or no power during flight and are often held out of the way of the hind wings.

Insects possessing tegmina include:

Earwigs

Grasshoppers and Crickets

Cockroaches

Mantids