This was a discovery for me. Certainly I’ve seen people build houses for dogs and birds, but never butterflies.
When my lens first spied these I mistook them for birdhouses. On closer inspection, I saw they were quite small and the doorways were shaped like slits instead of circles. Have you ever seen these? Why would a butterfly use one of these?
I did some research and found no reports that butterflies are using these houses. People have tried putting banana peels and overripe fruit in them as an enticement. Even that isn’t working to attract butterflies. The animals taking up residence are spiders, bees, and assorted insects. There was one report of a bird that liked the house so much that she laboriously worked to enlarge the bottom of a slit so that she could use the house for her nest.
If your objective is to do something for butterflies, the houses are not a good choice. On the other hand, they do make charming decorations for a garden or back yard. My thought is that you might as well make a hole large enough for a bird.