What’s the difference between a moth and a butterfly? There are a few differences but for every characteristic there are some exceptions. For example moths generally fly at night… but not all of them. Another difference is their antenna — if it has a club or hook shape it’s almost certainly a butterfly… but not always. Butterflies tend to have skinnier bodies while moths are fatter… but again there are exceptions. We take each insect as a whole and decide if it’s one or the other.