I witnessed some courtship behavior in silvery checkerspots, Chlosyne nycteis today.
It seems the female is in front–it is slightly larger than the male. Both sit on a leaf, and the female rapidly vibrates with her tail raised. The male does not vibrate but just sits there.
The male shows an active interest and occasionally flies around the female.
There is a flurry of activity but sooner or later they end up in about the same position.
Then the behavior repeats itself.
I did not witness the end of the courtship–there may have been some activity at the beginning I missed as well. I did see a number of these little vibrating dances followed by a chase. The chases and dances went on for some time and were fascinating to watch.