Usually it’s easy to distinguish a moth from a butterfly. Moths are generally nocturnal; butterflies operate in the daytime. Moths have furry, chunky bodies; butterflies are sleeker with less “hair”.
A white-lined sphinx moth warmed itself on my outdoor light fixture late one night.
Hummingbird clearwing moths feed on flowers open in the daytime — so, the nocturnal-only attribute for moths has many exceptions.
How about this diurnally-active leadplant flower moth? Easy to confuse with a butterfly, except that butterflies usually hold their wings vertically at rest while moths rest with their wings outspread or in a V-position, like the wings of a jet plane.
A Monarch butterfly sips nectar from the flowers of a rough blazing star plant. On chilly days, butterflies might bask with their wings open, but usually they sit with the wings vertical at rest.
Butterflies generally have slender, clubbed antennae; moths sometimes have elaborate fringes on their antennae or have slender filamentous antennae without clubbed ends.
Ropy antennae with clubs on the end are characteristic of most butterflies, like this Red Admiral feasting on a coneflower.
The elaborate, feathery antennae of the male silkworm moth can detect the bombycol molecules released by a female moth from a mile away. Photo by Ash Bowie from Wikimedia Commons.
As expected, the compound eye of moths differs from that of the butterfly — each being highly adapted to the light intensity of the environment in which the animal is most active.
Butterflies generally have compound eyes adapted for color vision in bright light, with multiple darkened areas that probably represent clusters of ommatidia used as specific focal points.
The compound eyes of moths are specialized for visual acuity in dim light. They appear more uniform in color, lacking the dark spots seen in the butterfly eye. Note the slender, filmentous antennae of this moth — very unlike a butterfly’s.
A final important difference between butterflies and moths is the pupal case, which may be a smooth chrysalis in butterflies but is a webby, textured cocoon in moths.
But then just to confuse things a little, we have the hairy-bodied skipper butterflies, with their densely haired bodies and their habit of sitting with wings spread rather than vertical. But ropy antennae with clubs on the end means that these guys should be grouped with the butterflies.
You can read more about this group of butterflies here.