Catch jars are easy to make and can help when trying to identify butterflies. Simply take a clear plastic jar, clean it thoroughly, and drill small holes in the lid.
Once you have a butterfly in the net, it is easy to slide the catch jar into the net and gently coax the butterfly into it. Make sure to avoid trapping the butterfly between the outside of the jar and the net. You can then slide the lid on the jar. This allows you to view the butterfly clearly while paging through a field guide. Do not put more than one butterfly in the jar at a time, and release the butterfly within a few minutes. Never keep a butterfly captive for a long time in either a net or a catch jar.