Thanks for your replies.
Re: our location = Indiana. Winter tones down in Feb, with only occasional freezing in March; now we're consistently 50+ during day and 40+ at night - but still early for flies to be in air. But I would guess it's prime time for larval activity.
Re: scratching - the...
I noticed a bit of bright red blood on the underside of a 4 yr-old bred cow (weather just now turning to spring). upon closer inspection there were a series of 6 lesions following the midpoint of her lower stomach along a line 18 in long up including her navel. I presume they are some sort of...