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primitive winged insects had no wing folding mechanisms in contrast to modern

advanced insects and they used to glide in the air.

The wing membranes are supported by a number of longitudinal veins, which

also have cross-connections that form closed “cells” in the membrane. The patterns

resulting from the fusion and cross-connection of the wing veins are often diagnostic

features for different evolutionary lineages and can be used in the classification and

identification of the family or even at the genus level in many orders of insects.

The wing venation is subjected to variations in various orders; however, it appears

characteristic for each order for taxonomy.

The wings may be present only in one sex as in male; rarely, female (as in figwasps)

and in some velvet ants. They are selectively lost in “workers” of social insects such

as ants and termites. In some cases, wings are present only at a particular part of

the life cycle. The structure and colouration of the wing will often vary. At rest, the

wings may be flat or folded on the abdomen, where the forewings cover the folded

hindwings. In foraging insects like bees, wings withstand wear and tear. In beetles

and bugs, the second pair of wings have resilinous patches contributing to wing

deformations and efficiency of flight.

The evolution of insect wings is not well understood. The four main theories for

the evolution of wings are as follows:

1.

Wings are developed from paranotal lobes such as extensions of the thoracic

integument from the pleuron.

2.

They are modifications of movable abdominal gills as found in aquatic naiads

(nymphs) of mayflies.

3.

Insect wings arose from the fusion of pre-existing endites and exites of

crustaceans.

4.

Insects have long been separated from other vertebrate fliers phylogenetically,

morphologically and structurally. However, their wings develop similar aero-

dynamic adaptation forces for flight. This is a very good example of analo-

gous structures developing homologous aerodynamic forces during a prolonged

course of evolution.

Distinct wing morphology (design) is a characteristic feature of many insect

orders. Wing textures in different orders of insects are discussed in the following

sections. Wing texture has been explained to understand their ecological adaptability

and aerodynamic requirements in different types of flight.

Orthoptera

The forewings of grasshopper are elliptical leathery or parchment-like opaque

tegmina and are narrow (Fig. 5.1). Like the elytra of beetles and the hemelytra

of plant bugs, the tegmina help to protect the delicate hindwings. The hindwings are

broad, membranous and folded in a fan-like manner. Locusts are known for their

long-distance migration covering 5000 kms on their wings. The wing design must be