This is another one of the Callophrys-Incisalia-Mitoura
group, which the genus-lumpers place with all the others in Callophrys,
but the genus-splitters place in Incisalia. This butterfly was long regarded
as a subspecies, mossii of Incisalia fotis,
known as the Early Elfin, but it has now been promoted to full species with
the name Moss's Elfin (you have a choice as to whether to write the third s!),
while Incisalia (or Callophrys) fotis becomes the Desert
Elfin, which does not occur in Canada. I suspect that the last word has not
been written on this group of genera.
The butterfly is on the wing early in the spring. Eggs are laid on the buds of Sedum, in the yellow flowers of which the caterpillars are well camouflaged. The pupa overwinters.