It may be inferred from these definitions that the distinction between the two sub-Orders is neither sharply defined nor of great importance. The club of the antenna of the Rhopalocera exhibits considerable variety in form (Fig. 176).[[210]] Butterflies are as a rule diurnal in their activity and moths nocturnal; but in the tropics there are numerous Heterocera that are diurnal, and many of these resemble butterflies not only in colour but even in the shapes of their wings.
Series I. Rhopalocera. Butterflies.
Classification and Families of Butterflies. Although considerable unanimity exists as to the natural groups of butterflies, there is much diversity of opinion as to what divisions are of equivalent value—some treating as sub-families groups that others call families—and as to the way the families should be combined. There is, however, a general agreement that the Hesperiidae are the most distinct of the families, and E. Reuter considers them a distinct sub-Order with the name Grypocera.[[211]]
Four categories may be readily distinguished, as follows, viz:—
1. The majority of butterflies; having the first pair of legs more or less strikingly different from the other pairs; frequently very much smaller and not used as legs; when not very small, then differing according to sex of the same species, being smaller in the male than in the female; the part most peculiar is the tarsus, which is modified in various manners, but in the males of this great series is always destitute of its natural form of a succession of simple joints five in number. There is no pad on the front tibia.
Fam. Nymphalidae, Erycinidae, Lycaenidae.
[The distinctions between these three families are found in the amount and kind of the abortion of the front legs; for definition refer to the heading of each of the families.]
2. The front legs are in general form like the other pairs; their tibiae have no pads; the claws of all the feet are bifid, and there is an empodium in connection with them.
Fam. Pieridae.
3. The front legs are like the other pairs; their tibiae however possess pads; the claws are large, not bifid, and there is no empodium; the metanotum is completely exposed at the base of the abdomen.