Poop with worms I think

A small amount of poop this week has had threads that look like cress seedlings without the green leaves.  There has not been enough for it to be more than one hen (I have four) and they all look healthy.  Presume this is some kind of worm picked up while foraging around the garden.  Advice please.  Everything I have read so far goes on about much nastier worms.  I looked at the poop pics and they look like one of those.  Treatment? Panic or not?
Also they are now on their winter quarters on concrete covered with playbark.  How often should I replace the bark?  Once a month?
Hoping the brown rectangle that was my lawn may recover.
Would it be a wicked thing to keep them on the concrete all year, letting them out to roam every day for an hour or more (depending on the day-length)?

I battled out into the wind, camera in hand, but there was no wormy poop.  I clear it all out midweek and then do a thorough clean on a weekend, so there has been no wormy poop since Wednesday.  Looking at the photos on this site it looks like the very last one therefore is probably Ascaridia galli as it says there.  But what now?
There is nowhere local to buy anything so I will go on the net presumably to get a wormer?  Chickens still look fine.  And laying 3 or 4 eggs a day between them.
Grateful for your replies.

 Could possibly be grass that has passed through......mine eat a lot of grass and often there is quite a bit that has passed through looking stringy.