Intense rubbing causes a roughened tail head that is cosmetically objectionable and undesirable. Lungworm infections are rare, but young horses can be seriously affected. This worm lives in the bronchi and trachea, causing a persistent cough and respiratory complications. There are several skin problems your horse can get from biting insects. One is summer sores, which are caused by part of the cycle of the stomach worm.
Flies deposit stomach worm larvae in skin lesions and some body areas, thus causing summers sores.
Another internal parasite, the neck threadworm, requires gnats for transmission of infection. Its microscopic larvae are found in the skin, usually on the horse's chest. This causes dermatitis, or summer itch. Biting gnats pick up the larvae from the affect skin and transmit the infection to other horses. Specific parasites require specific action.