That might be diatomaceuos earth, [member=8427]BML[/member] .
I don't know what the 'What do you want to do ?CopyWhat! Thinking Chickens?' stuff is, but I agree with [member=168910]Perris[/member] .
It could be red mite which Diatom might help with but it needs to be spread liberally in the nest boxes and on the perches, and also inside the roof of the coop. If it doesn't work you may need something stronger. You might be able to see the red mites if it's dark inside the coop and you shine a torch on the ends of the perches or in teh nest boxes