Collections of Nematospiroides dubius were made from feral Mus musculus in 1939 and Peromyscus maniculatus gambelii in 1950 near Davis, California. The life cycle follows the tricho-strongylid pattern. The pre-patient period occupies 9 days, and the patent period may be as long as 8 months. Variations in length of pre-patent and patent periods are induced by the strain and age of the host.