Get a magnifying lens and look at one of those bugs. Count the legs. If it has eight legs, then it's a mite.
Next, go out to your coop after dark with a flashlight and a couple of white damp rags. Wipe the perch where one of your chickens is roosting. If the rag is smeared with red, you have coop mites. Wipe a fresh damp rag over a leg of the chicken. If it is smeared with red, mites are also on your chickens and you will need to treat your coop to rid it of mites as they are biting your chickens and that can lead to health problems.
Do you keep your chicken feed in the coop? If so, these bugs could be grain mites. If your wipe test fails to produce red smears, an indication the mites are biting the chickens, these grain mites are creepy but harmless. However, grain mites indicate the feed is becoming damp and that can lead to mold which can cause toxic reactions in your chickens.