Schematic life-cycle of Spirocercal lupi . Eggs containing L1 larvae are found in the feces of the infected canid host (Feces: L1). The intermediate host, a dung beetle, consumes the feces and ingest the eggs (A). The eggs hatch and the larvae develop into L3 (Intermediate host: L1-L3). The intermediate host can either be consumed by paratenic hosts such as birds or small mammals (B), in which L3 arrest their development (paratenic host: L3), or by the definitive host (C) where the L3 larvae are released in the stomach, penetrate the gastric mucosa and migrate within blood vessel walls to the caudal thoracic aortic wall, where they develop to L4. From there, larvae migrate to the caudal esophagus, where they mature and sexually reproduce (E, Definitive host: L3-L5). Alternatively, the definitive host preys on L3 infected paratenic hosts (D). Adult worms are found in the esophageal wall, surrounded by a nodule. The female worms pass their eggs to the gastrointestinal tract, and into the feces (F, Definitive host: L5-eggs).