This is a beautiful book. I started reading it on my black-and-white ereader and quickly realized I was missing out, so I read it in full color, large image size on my computer. The pictures are breathtaking. A large fraction of bioluminescent creatures are deep-sea creatures -- hence the nasty ugly picture on the cover. Yes, fireflies would've been cooler. But there's some wicked cool creatures down deep, and they do weird things.
There are some good little stories in here about the process of science and how we know what we know about creatures that glow naturally. It's brief but very informative.
But only the first half or so is about creatures that bioluminesce (okay, maybe a little more than half). The last couple chapters are on how we use bioluminescence in research and what it has helped us learn. There's a section of quarum-sensing in bacteria, which is fascinating and I had never heard of it. We can also trace just about any gene through an organism by making it glow. Really intriguing stuff.
So even though you've probably not thought a lot about glowing animals, there's some really neat things to learn in here. The publisher calls it a junior science book, and it's certainly accessible to junior high school students. Things are explained well and there are great pictures. But it isn't dumbed down or oversimplified. I would say something like 6th grade and up. All the way to adulthood. I bet you'll learn something from it.
I got a free copy of this from Net Galley.