Around here they can kill a Deer which they do often. When it gets hot they can be seen in the air in bunches. Looks like a dark cloud. It's recommended not to go out until they're gone. They get in the eyes and cause disease. they have made humans very ill. They didn't seem to bother my chickens maybe becaue they are in the shade maybe and a breezy part of the yard. I will put in a fan soon. They have already started around here. I'll get some fly paper too, just in case.