Hi there -
I just wanted to add info on this possible biting pest that can reside in hay and straw:
Also a good source for helping to diagnose source of bites and itching:
I recently moved to a place with lots of annual grasses that the chickens love - lots of wild oats. I have been cutting the oats down now for the approaching fire season, and in the last week or so have gotten totally covered with bites.
At first I thought, from looking around, they were no-see-ums, but this picture in the link above looks just like me - and I've got one bite in the elbow crevice as mentioned. Unfortunately I think my entire yard is infested with these guys. Worried about the chickens too.