What is the single most reliable physical characteristic used to separate moths from butterflies?

Answer

Antennae structure

The antennae are perhaps the single most reliable physical characteristic used to separate moths from butterflies, even in species active during the day. Moths usually have feathery or comb-like antennae, while butterflies have slender antennae ending in a distinct club.

What is the single most reliable physical characteristic used to separate moths from butterflies?
insectmothanatomycharacteristicphysical