I had never heard of Butterfly Houses prior to my wife mentioning them a few years ago. And since then, I've made several of them based on pictures I'd seen on the internet. The theory is that butterflies wanting a safe place to lay their eggs will make use of these boxes sometime in the Fall. Inside of them you put a small tree branch (I've heard that Birch works well), and for this, you put a door on these boxes. Personally, I think they're more useful (and desired) as decorative ornaments, so I tend to gussy them up, as I did with this one. I'll separately post other similar ones I've made.
The one shone in these pics I made for my sister-in-law. It was made in Alaskan Yellow Cedar, which I burned/charred using a Sho Sugi-Ban technique, after which, I tinted the wood in a two-tone fashion that you see in the pics, and then finished it using Spar Urethane to give it added UV/rain protection. The door is hinged with brass rods, and a latch that keeps it from blowing open on wide days. Lastly, I added a hand-hammered brass roof ridge.