I can't remember either title or author, but there was a short story from
the sixties about a group of alien missionaries who came to earth
proselytizing their own religion. They were giant caterpillar-like beings
whose savior metamorphosed into a moth or butterfly. Eventually, they went
around destroying the great cathedrals and chruches of Earth and building
their own temples to their Savior on the same spots, and tried to force
conversions at the point of a blaster.

The author made a very pointed comparison to the European (Spanish)
explorers and Native Americans, and I'm not certain how the story ended.
Has anyone else read this?

Steve Collins