Strongyle nematodes from the Strongylida suborder, referred to often as "large strongyles", are one of the most significant gastrointestinal parasites in horses worldwide. The three most common large strongyles that affect horses are Strongylus edentatus, S. equinus, and S. vulgaris. While living inside of the horse's GI system, they will produce eggs that get passed from the horse via feces. While living in the feces, the eggs will start to develop and turn into infective third-stage larvae and contaminate the environment surrounding the feces. Either the same horse, or other horses that graze on the same pasture may ingest the larvae while grazing. Once ingested, the strongyle larvae migrate to specific organs within the horse's body; each strongyle species has a preference for specific organs. For example, S. vulgaris are usually found in the horse's vascular system, S. edentatus in the liver and retroperitoneum, and S. equinus in the liver and pancreas. Thromboembolic colic is caused by migration of larval stages of S. vulgaris.