What are these little black critters?

[NEWTODUCKS]

When I clean my duck house out there are hundreds of these small black critters,they crawl and jump about particularly in the damp shavings.
I clean my ducks out weekly, they have an airy wooden house. I place a plastic sheet on the base, covered with a thick layer of newspaper and then a thick layer of shavings.I clean them out first thing in the morning and then leave it all day to air/dry out. Can't think what else I should be doing to keep their house any cleaner.I have in the past scattered red mite powder-not that I think it's them but in the hope it would kill them but it hasn't worked.
The ducks themselves are fine and I am pretty sure these critters are not on the ducks but would like naturally to eliminate them.

 

[dorsetduckowner]

Can't see the picky but in my duck house this time of year there are hundreds of baby flies. Took me a while to figure what they were. I dust with mite powder just I'm case but could they be baby flies?

 

[NEWTODUCKS]

Thanks for the reply-the only other clue I can offer is that I put the used shavings from the duck house in the green wheely bin which is collected every 2 weeks and I have noticed maggots crawling on the lid-much to the delight of a passing hen! I assume the black critters/maggots are related but maybe not. These black things are not flying but can jump,will just have to keep removing the blighters!