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. There was a sign nearby stating they were for butterflies. 

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 and bees. 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. 

See imagesbyvandyne on etsy.com for more photos.