My daughter takes riding lessons with a lady who has a bunch of horses. She is having a bad bug problem this year. She had been keeping chickens and guineas to take care of much of the problem, but there is a pair of foxes near her property she hasn't been able to get rid of that are making it impossible to keep poultry. She has a lot of mosquitoes and biting flies. The biting flies are so bad that the horses' faces get bloody from it. What do you horse keepers do to deal with mosquitoes and biting flies?