Butterflies are insects, which like all arthropods (also including spiders, scorpions, millipedes, lobsters) have jointed legs and a 'shell' on the outside of the body (an exoskeleton), enclosing the soft parts. Like all insects, butterflies have three major body parts; a head, thorax and abdomen. Like insects, butterflies have three pair of legs, though in some groups the first pair of legs has been reduced so much that they are virtually useless for walking and are only apparent on closer examination.
Butterflies belong to the order Lepidoptera — Greek for 'scale wings', as their thin membrane wings are covered by loose scales. Actually, only about 12% of this order (Lepidoptera comprising more than 165,000 species) are butterflies, the rest being moths. Butterflies and moths have two pairs of wings, originating from the thorax; 2 forewings, 2 hindwings, which are cut by complex patterns of veins, varying between the different species.
Below: Small Tortoiseshell (Aglais urticae), showing characteristic butterfly features discussed
Unlike most moths, butterflies are active during the day, usually only when it is sunny and bright. When butterflies rest, their wings are pressed or folded together in a vertical plane, above the body (abdomen) so that the lower surfaces of the wings are exposed — most moths rest with their wings held flat, concealing the abdomen. Unlike moths, the two antennae end in clubs.
Below: Red Admiral (Vanessa atalanta), feeding on buddleia, showing resting position with wings closed.
The bright colours and spectacular markings which often adorn butterfly wings are either due to presence of pigments in the wing-scales, or may be due to the way the microscopic structure of the scale interferes with light (the diffraction of incidence light), the latter of which produces the metallic colours of butterflies, as in the group known as the 'blues' (Lycaenidae). Colour may serve several functions: to avoid predation through camouflage (normally visible on the under-surfaces of the wings), for attracting a possible mate (visible on wing upper-surfaces), and may also be used to raise body temperature, as the butterfly basks in the sun.
