Any ideas?

My Wildlife book is in the caravan and Google didn't help.  Could be just a house fly but there's another view in Extra and you'll see it's brown, not black?  ppl or someone to the rescue, please.  I spotted him on the Green bin busily hoovering up what looked  like just dust?

I've got some more jobs ticked off the list, unfortunately mostly indoors so I've missed the gorgeous. and rare shower-free day.