Because if they are, they are part of the Armadillidium group of critters. I love them. They do break things down into smaller pieces. I understand that chickens love them. I know some people, to either get rid of them or to feedchickens, place flat stones or pieces of wood, sometimes with food scraps underneath, out in the yard in the evening, to return the following morning to harvest the yield from their pill bug traps (these guys are colloquially known as sow bugs, pill bugs, potato bugs, and my personal favourite, rolly-pollies, after the way some can roll themselves up for protection against most things that aren't chickens).
Try to get a picture if you can, probably using the trap method. Good luck.
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein