It appears to be a Western Tiger Swallowtail (
Papilio rutulus), based on it being green rather than brown as in Canadian Tiger Swallowtail (
P. canadensis)... I don't know much about butterfiles and I don't know if this is reliable distinction, so just a guess on my part. The larvae of both feed on poplars, willows and cherries.
Terrific find! It always seems strange to me how few butterflies and moths, or even insects in general, there are in Calgary. Our yard has ample bloom all through the season and yet butterflies and moths are few and far between. A few years ago when the Painted Ladies had their big irruption, was the only time I've seen something like a "normal" number of butterflies here.
