Insects In My Moss

I bought a tray of Christmas Moss on ebay and it arrived this morning.
It looks very healthy, more green that the last  lot I bought on there anyway.
What worries me I that when I took the cover off to place it in a tub of water, there were loads of little thread like flies in the tray.  The crawled rather than flew.
I have emailed the seller but he hasn't replied.

Is it normal and if so what are they please

Thanks Richard. If they are grown "dry" then that would explain it.
It is very healthy looking and I did dump it straight in water.
I refreshed the water this morning and loads of little black bits came out.
I'm sure they weren't flies, they didn't swarm when I uncovered them, they crawled but they are very tiny.
I've no doubt the fish would have made short work of them, just didn't want to take a chance of introducing something unpleasant into the second tank, which is cycling very nicely.

I do think it's a bit "off" that the seller never replied, but them I had stupidly already left positive feedback on the basis of how nice it looked.
I'll rinse them every day until they are ready to be used which wont be for a week or more yet.