Butterflies and moths are scale winged insects, and are among the giants of the insect world; they can be defined as insects with two pairs of membranous wings well adapted for extended flight, clothed with scales overlapping each other like the slates on the roof of a house, flattened and rounded on the surface of the wings, but more or less hair-like upon the body. The head is usually provided with a tubular proboscis or mouth, that can be curled up like a watch spring when at rest, and is admirably adapted for sucking up the honey from flowers when expanded. The caterpillars may be smooth and naked, or thickly clothed with spines or hair; with few exceptions they feed upon the foliage or wood of plants: after undergoing a series of moults they either spin a cocoon, bury themselves in the ground, or (if wood borers) close themselves up in the burrow where they undergo a complete metamorphosis. If the larva of a butterfly, the caterpillar attaches itself to a twig by the tip of its tail and casts the larval skin, which slips off, leaving the naked transformed pupa simply enclosed in a stout, close-fitting pupal jacket. Some species of moths appear in such numbers at times that they do a great deal of damage to plant life, and are very serious pests. Lepidoptera on account of their beauty and size have always been very popular with entomologists, and large numbers have been collected from all parts of the world, so that this is one of the best known orders. Sharp estimates that 50,000 species are described, and every year adds to this long list. They are divided into two great groups, somewhat artificial, but definable as RHOPALOCERA, butterflies; and HETEROCERA, moths. RHOPALOCERA. Butterflies. The typical butterflies are usually slender-bodied insects, with filiform and more or less clubbed antennae, delicate legs, and large richly tinted wings; they fly about in the bright sunlight, visiting flowers and feasting upon the nectar that they find in the blooms. They have large compound eyes so that they can see very well; and the slender tubular mouth is very highly developed in all butterflies. The eggs are laid upon the food plant: the caterpillars are generally more or less elongated, and naked or covered with scattered tubercles rather than hairy; when full grown they attach themselves to the under side of a twig or leaf by the tip of the abdomen. Some groups are furnished with a silken girdle round the middle attached at each end to the leaf or twig; and another section roll themselves up in leaves. They do not form a cocoon, but as the larval skin slips off, it reveals the regular pupal form fitted with a skin-like jacket through which the indistinct lines of the rudimentary wings, legs and antennae can be traced. The pupa may remain in this quiescent state for several months before the butterfly splits the skin and emerges, a perfect, fully developed insect.