Answer: When it’s a Kingfisher box.
Okay, here’s the story. In 2008 a Kingfisher box was built for a client targeting only the Australian Kingfisher. As the image shows the dimensions are slightly larger than a shoebox. Installed on a horizontal plane with a side entrance it would have been perfect for the bird that we wanted.
But low and behold during a routine box inspection guess what I found? Yes, micro bats. Have a good look and what they’re hanging onto. Yes, you guessed it. The plain untouched timber walls. This goes to show that they can really grip almost anything. So next time you are building your own bat box just score the front and side walls with a knife. The rear needs to be mesh. This makes it easy for the bats to land on and climb up.
By the way the white “eggshell” in the foreground is really a spiders egg sack. You see the Huntsman spiders share the same abode without getting eaten.