I unknowingly fed out hay last winter that did contain some blister beetles (at least i suspect that's what they were). No one in my area (Calgary, Alberta) has even heard of these - not even the large hay company I now buy my hay from.
I just right now phoned the lovely couple that I bought hay from last year to tell them of my suspisions. It was awkard as we are friendly with them, but I had to let her know that I thought they had these beeltes in their hay fields before anybody else's horses are put at risk Luckily my guy was ok but it KILLS me to think that he was at exposed to this and I had no idea.
Just add to the list of terrible things I have done to him without lately! (His teeth were over-floated in December, and as a result got ulcers. Sometimes I think he'd be better sitting in a field left alone to fend for himself. At least noone would be trying to poison him and make it so the poor boy can't chew Faaaa.)