DE stands for Diatomaceous earth- which is essentially the fossils of tiny algae. It works by absorbing the lipids away from the insect's waxy coating of their exoskeletons, therby dehydrating them. It has TONS of uses, and is a chicken-keeper's best friend and a must have! However, YOU MUST BE SURE TO GET FOOD GRADE!!! This is much more fine than that used for gardens and pools, and will not harm you or your chickens if ingested. The other, the industrial stuff, pool or garden form, is too abrasive and could cause harm when ingested. You can use food-grade DE inside your coops, and some people even use it as a worm preventative, for chickens, as well as dogs, cats, etc. It is not a good wormer if you have an active infestation- but my understanding is that it helps to prevent such problems. Best of luck, hope this helps!