During the infective stage of the S. vulgaris life cycle, the larvae that have matured in the intestinal tract of the horse will migrate into the surrounding blood vessels. Once in the blood vessels, the larvae will continue their migration throughout the body to various organs causing damage to the blood vessels along the way. This can cause anemia or blockage of blood flow caused by the detachment of blood clots from the vessel wall resulting in tissue death.
S. vulgaris are commonly found in pastures and stalls where feces are present. The larvae crawl up on the grass which is where they are then eaten by the horse. Harsh environments, such as freezing, do not kill S. vulgaris.