According to the childhood me, these are the most fun bugs ever. I remember having so much fun watching them roll up into little balls.
What’s really interesting about them is that they aren’t insects at all. They are actually terrestrial crustaceans. They’ll usually be found in damp locations feeding on moss algea or other decaying organic matter. They like moist areas, not just for the food, but also because, since they breathe using a type of gill, they must remain moist to survive. They have a typical lifespan of 2 to 3 years.
(Don’t tell the spider from the previous post that these guys are up here!)