I need help identifying this "worm" or possibly larvae. A little background: About two weeks ago, one hen had a huge poop which look like milk poured on the ground. I took her to the vet. They identified a large number of spore forming bacteria in her poop and a mild upper respiratory infection, but were unable to give a specific diagnosis. They put her on an antibiotic and an antiparasite medicine. She has been quarantined. She has not fully recovered, poops have improved but not normal, some appetite but not normal yet. Yesterday we added more sandbox grade sand to the run area. Last night we had a rain. I went out this morning and there was small puddle in the run with about 15 of these "worms" floating and swimming in it. By the time I came back in to get to get my camera, there was only one left. All "worms" were the same length, approximately 0.5". They all had a dark spot on one end. Any ideas what they are? I'm wondering if they could give a clue for my sick hen. Many thanks.