Didn't know that. I really want to make a BSF box
Discussion
Apparently you can feed BSFL exclusively on coffee ground, so if you have a coffee shop near you you may be able to get free food for them.
There's a lot of good info in this Living Web Farm playlisthttps://www.youtube.com/playlist?list=PLCeA6DzL9P4v7rQeRdfQoPI2QgiIl785j