The division butterflies and moths is rather artificial and is one of convenience rather than being based on scientific principles. In general, butterflies are day-flying, hold their wings open at rest and have clubbed antennae. Moths, on the other hand are usually nocturnal, rest with their wings folded over their body and do not have clubbed antennae. There are, of course, numerous exceptions to these generalisations. For example, Burnet Moths are both day-flying and have clubbed antennae, although they do rest with their narrow wings folded. Another example are the geometrid moths, most of which rest with their wings open, although they are mostly nocturnal and do not have clubbed antennae.
The separation of macromoths and micromoths is even more arbitrary, containing several anomolies with respect to which families are regarded as belonging to each group. These groupings have a historical rather than scientific basis and arose due to many of the smaller moths being very difficult to identify, leading most lepidopterists to ignore them and just concentrate on the larger species. Obviously, there is considerable overlap in size, with many moths that are classified as belonging to the macromoth families being smaller than some of the micromoths, and vice versa.
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