May be impossible to know for sure...I seriously doubt they could have come with hatchery chicks.
I just learned the other day that red mites can be carried by rodents:
http://www.poultrydvm.com/condition/poultry-red-mites
I too doubt they could have come with hatchery chicks, but I can't be certain either.
Red mites; that is possible. Usually red mites are everywhere around here though it seems. I know they can be devastating to some coniferous landscape plants; at least from my own experience. They're usually all over the concrete patio's around here and are tuff to kill. Even harsh winters don't seem to stop them...I'm not even sure I buy into it that harsh winters kill insects anyway. It may happen to some, but I don't tend to think that large numbers of any kind of insects are killed by harsh freezing winters.