Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how insects fly is imperfect. One application of this research is in the engineering of extremely small micro air vehicles with low Reynolds numbers. Insect wings are adult outgrowths of the insect exoskeleton that enable insects to fly. They are found on the second and third thoracic segments (the mesothorax and metathorax), and the two pairs are often referred to as the forewings and hindwings, respectively, though a few insects lack hindwings, even rudiments. Insect wings do not constitute appendages in technical parlance, as insects only have one pair of appendages per segment. The wings are strengthened by a number of longitudinal veins, which often have cross-connections that form closed "cells" in the membrane (extreme examples include Odonata and Neuroptera). The patterns resulting from the fusion and cross-connection of the wing veins are often diagnostic for different evolutionary lineages and can be used for identification to the family or even genus level in many orders of insects.
The physical dynamics of flight are composed of direct and indirect flight. Those species that employ direct flight have wing muscles directly attached to the wing base, so that a small downward movement of the wing base lifts the wing itself upward. However, insects with indirect flight have muscles that attach to the thorax and deform it; since the wings are extensions of the thoracic exoskeleton, the deformations of the thorax cause the wings to move as well.
c. 70 spp., see text
Eurema is a widespread genus of grass yellow butterflies in the family Pieridae.
The Common Palmfly, Elymnias hypermnestra, is a species of satyrid butterfly found in south Asia.
As some other species in the genus Elymnias, the Common Palmfly presents a precostal cell on the hindwings and a hair tuft of androconial scales on dorsal discal cell of hindwings. This butterfly species is dimorphic, males and females do not look alike. Males exhibit black colored upperside forewings with small blue patches and reddish brown color on upperside hindwings, while the females mimic butterfly species of the genus Danaus.
The Tailed Orange (Eurema proterpia) is a North and South American butterfly in the family Pieridae.
The upper side of the wings is orange with a variable amount of black along the fore wing costa. The wing veins are lightly marked with black in summer individuals, and winter individuals have no black veins. Males reflect UV light on their upper sides, and some females can be white. The underside of the wings varies depending on the season. Summer individuals are yellow-orange with the hind wing slightly pointed. Winter individuals are brown with darker brown markings with the hind wing being much more pointed. The wingspan measures 1¼ to 1¾ inches.