Don't know a whole lot about it, but as far as I can tell it's pretty good. Normally when I see one it gets used heavily; the holes by all kinds of mason bees a

Don't know a whole lot about it, but as far as I can tell it's pretty good. Normally when I see one it gets used heavily; the holes by all kinds of mason bees and the rest as shelter/housing for other insects. Only possible problem: the wood shouldn't be treated (as a precaution, not sure if there is actual impact of chemicals on the bees in it). And when birds like woodpeckers discover this it's a feast and they will empty the whole thing but that's sort of natural in that it's normal behavior. But a construction like this of course makes it extra easy for them. Can be circumvented with steel wire 10cm in front of it.