Paratenesis between paratenic hosts was also shown to be possible in these 3 species. Data from naturally infected mayflies, Callibaetus sp., show that encystment and survival of gordiids within aquatic insects occur in nature. Subsequent infection trials of definitive hosts with cysts from imagos show that cysts surviving the metamorphosis of insects remained viable and free of host internal defense reaction. Cysts of all 3 species survived the metamorphosis of Tanytarsus sp., a midge. This proposed life cycle was experimentally tested using 3 common American species of gordiids: Gordius robustus, Paragordius varius, and Chordodes morgani. This has led many investigators to suggest that infections are acquired through the ingestion of insects, which become infected as aquatic larvae with gordiid cysts and subsequently carry gordiids to land. However, epibenthic aquatic larvae and their terrestrial definitive hosts do not overlap in habitat. To complete their life cycle, gordiids must make a transition from aquatic to terrestrial environments.
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