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The life cycle of the lungworm Protostrongylus boughtoni Goble and Dougherty, 1943 was completed in intermediate and definitive hosts. Larvae developed to the infective third-stage in the foot of the snail Vallonia pulchella (Miiller, 1774) in 28–30 days at 18 °C. First-, second-, third-, and fourth-stage larvae are described. Patent infections developed in laboratory-reared snowshoe hares, Lepus americanus americanus, each given 50 third-stage P. boughtoni larvae per os 25 to 27 days postexposure. Periods of patency ranged from 41 to 104 days. Patent infections developed in domestic rabbits, Oryctolagus cuniculus, Dutch Belted strain, given 50 or 150 larvae in 25 to 26 days postexposure, but periods of patency ranged from 7 to 13 days and larval output was very low.

The snail Triodopsis multilineata (Say) and the slugs Deroceras laeve (Müller) and Deroceras reticulatum (Müller) were successfully reared using inorganic vermiculite as a substrate and carrots and lettuce as food. Discus cronkhitei (Newcomb), Vallonia gracilicosta Reinhardt, Vallonia pulchella (Müller), Vertigo gouldii (Binney), and Zonitoides arboreus (Say) were reared on various types of organic leaf-litter substrates that simulated their natural environments. Triodopsis multilineata was the gastropod most easily reared and maintained.

Natural infections of Protostrongylus boughtoni in intermediate and definitive hosts were examined in Boreal Forest habitats of north central Alberta. Vertigo gouldi was the major intermediate host. Prevalence and intensity of P. boughtoni larvae in V. gouldi were similar among habitats, among size classes of V. gouldi, and temporally. Prevalence of P. boughtoni in adult snowshoe hares was 100%; mean intensity varied monthly at relatively low levels. Juvenile snowshoe hares became infected within a month of birth; intensities increased to relatively high within 3 months and then declined, indicating development of an immune response or decreased exposure to infected snails. No evidence was found for transplacental transmission. Relative rates of flow of P. boughtoni were calculated to determine the importance of snail species and habitat types in transmission of the parasite. Vertigo gouldi accounted for nearly all flow from snails to hares, and most of the flow from snails to hares occurred in dry coniferous and mixed wood habitats.