Yup, I'm thinking those are maggots. I found those once in a big poop pile in my coop once too. Shortly afterward I cleaned the entire thing top to the bottom. Gross. After that, I started sprinkling diatomaceous earth (DE) on all the coop surfaces. Haven't had a problem with them since. I got it in a 50 lb bag at my feed store for like $15. You just have to make sure you get the food grade kind, NOT the kind that is made for use in pools. I have no idea how it is used in pools, I just know it's bad for the chickens. But then again, I would never use anything that isn't food grade, since I eat the eggs!
Could be any one a thousand varieties of insect larvae, put some in a mesh topped jar and see what develops...sorry, I'm a science experiment kind of folk.
...or give them to the chooks, they'll eat them up!
Zeolite, brand name Sweet PDZ, will dry the poop to discourage insects laying eggs in poop...it will also reduce ammonia odor.
DE will kill beneficial insects too, so you may not want to go that route.