I think if you broadened it to insects, you might have something here.
The first thing that came to mind was Jack Elam in the opening of OUATITW with the fly. I've always looked at this sort of thing as Leone presenting a more realistic Old West than say the average John Wayne western. The west was a dirty, stinky, nasty place and I'm guessing there was an overabundance of insects around whether it be cockroaches, beetles, or flies.
