Cloudless Sulphur, Phoebis sennae

This small to mid-sized butterfly was photographed in the ENMAX Conservatory at the Calgary Zoo on 1 September 2011.

"Their range is wide, from South America to southern Canada, in particular southwestern Ontario. They are most common from Argentina to southern Texas and Florida, but are often visitors outside this range becoming more rare further north." Wikipedia.

en.wikipedia.org/wiki/Phoebis_sennae