My flock has had fairly poopy butts lately; nothing runny, but just like they can't get it past their tail feathers. I grabbed one chicken to give her a trim and wash and found two round "sores" (they weren't red, brown, with no blood) filled with tiny, writhing creatures above her cloaca on either side (is that they correct word? It is like on the flap of skin above her rear). SO utterly horrible. I grabbed the hose and washed them, but I couldn't get the creatures out (they sort of stopped moving and contracted). Seriously vomitous operation. What are they? What do I do? Cannot be good. Her sister died on unknown cause last year, but it seemed like she had been eaten from the inside out.