In response to @mamestraconfigurata 's comment about not being able to sex ADULT lepis without dissection, I respectfully disagree.
For nocturnal lepis this is very easy as long as the antennae are visible (moths often fold the antennae under the wings, the unco-operative little so-and-sos ;-).
The females have filiform or pectinate antennae, and the males have bipectinate antennae. This is because the females give off the pheromones, and the males locate them using their (sometimes rather magnificent) antennae.
A couple of examples:
Streblote sp. (Lasiocampidae) LEFT: female RIGHT: male
Drepanogynis cnephaeogramma (Geometridae) TOP: female BOTTOM: male
(Note: the wing colours are not gender-specific, this is a highly variable species. It’s all in the antennae!)
There is a fascinating article by Hermann Staude about species of moths choosing to become diurnal, and the changes in who attracts who.
Nocturnal moths have the females sending the signals and the males with larger antennae to detect said signals. Whereas those moths that are fully diurnal have the males sending out the pheromones and the females coming to them.
Hermann shows how the switch to diurnalism is slow (evolutionarily speaking) because of the problem of detecting female pheromones during the day, so that some species have day-flying females, but the males are still nocturnal so that they can detect the females. An example is Speckle Orange Acanthovalva focularia - only males are attracted to light at night, and only females are caught in butterfly traps set out during the day.
Fascinating read - download it for free Metamorphosis 19 pg 35.
So, antennal characteristics are probably not as useful for diurnal moths and butterflies.
And now I’ve gone way off topic for which I apologise. This stuff is all so thrilling that I sometimes lose the plot ;-D