Things that have a history of being traded, especially from a limited area of origin, tend to have similar names. Coffee, tea, and sugar are examples of this; the names were exported with the commodity.
Butterflies can be found almost everywhere, and haven't been subject to any large-scale trade, so the speakers of each language have been free to make up their own names.
Oh yes, absolutely. It's usually easier to find etymologically related terms for the same thing among the most common romance languages (I'm a spanish speaker). Probably each region tended to keep the native name they gave to it before they were subjected to the latin influence.