The antennas of moths are usually "feathery" while those of butterflies tend to be smooth with knobs on the end. There are variations, however, and in some species it is difficult, and ultimately meaningless, to classify them as either butterflies or moths.

There are many variations in both the shape and the hairiness of the antennas, and this is one of the ways that closely related species and be distinguished. Insect antennas are sometimes called "feelers" and they are used that way, but they also have a sense of smell and taste.

The sense of smell of some species is so sensitive that they can detect minute amounts of pherenomes that are put out by the opposite sex and thus find them from miles away. Some spiders take advantage of this by producing substances that mimic the female's scent and thus lure males to their deaths. It is difficult for the moths to develop a defense against this because a male not attracted by the pherenome would not find a mate and wouldn't pass this trait on!