The antennae of Lepidoptera appear to be the main organs of smell. Many moth species fly only at night, or have flightless females, and so use pheromones for sexual attraction. Usually it is the female which emits the pheromone. which the males smell with the antennae. Their antennae have a feathery appearance.

male Pollanisus subdolosa, showing folded sensilla on the antennae.
(Photo : courtesy of Buck Richardson, Kuranda)

The lateral filaments on these antennae are called sensilla. The moths are able to fold or unfold these sensilla.

female Papilio aegeus, showing clubbbed antennae.

Butterflies fly in daylight, so in general appear to use sight rather than smell for sexual attraction, so their antennae are different. They have a bulge on the end of each antenna, like a small club.