Coordinator notes: You tendatively identified this butterfly as Uler's arctic but it is the Chryxus Arctic. Uhler's arctic occurs in forested areas but usually only in wide-open grassy areas among the trees or in fully open grassland or sagebrush-grassland parks (more common in western Colorado). Both may occur near each other in well forested areas (like where you were) but the Chryxus Arctic will be found where it is more treed. It is a larger species and the markings on the underside are more distinct and well defined than they are on Ulhler's Arctic. The Chryxus Arctic flys only during even numbered years in the Front Range of eastern Colorado and hence since this year is 2014 this was one of the years it is found. Rarely do you find one in the odd number year. Higher and farther into the mountains we have another species that looks much like O. chryxus but it is different. This is Oeneis calais. This arctic has been consider to belong to O. chryxus (the same species) but it really is not. You can find it in both odd and even numbered years but as mention, at higher altitude. There are few places where both occur together but I have identified one at Beaver Creek just north of Fairplay Colorado. I have each from this place during an even number year - in 2012.