This species is not only very common worldwide but also has a wide host range among families of the dipteran suborder Nematocera. Its usual hosts are larval Chironomidae and Simuliidae. For the second time in New Zealand we found S. simulii in nymphs of the endemic stonefly genus Zelandoperla (Plecoptera, Gripopterygidae), the only nondipteran host known. Infested Zelandoperla nymphs were found in Cron Creek, west of Haast Pass, South Island (site ZEA-97).
Smittium simulii was also found in a population of A. australense larvae in Thompsons Creek (site ZEA-77, Hwy. 85 near Omakau) and in simuliids in Lust Creek (site ZEA-71, Hwy. 87 N of Middlemarch). Infested chironomid larvae included Cricotopus aucklandensis (Sublette & Worth) (Silverstream); Tanytarsus vespertinus Hutton (Manuherikia River, site ZEA-80 1 km SE of Hawkdun); Maoridiamesa sp. (Waterfall Creek (site ZEA-93, discharging into Lake Wanaka) and a small waterfall on Hwy. 6 W of Haast Pass); and three other unidentified species of Chironomidae.

This was the most common species of Smittium we found in New Zealand. It has a worldwide distribution and a very wide host range. Though predominantly a commensal of Chironomidae and Simuliidae larvae, it has been found more rarely in Culicidae and Tipulidae larvae. We report here the first known occurrence in stonefly nymphs.
Our collections of S. simulii on North Island included sites 9, 11, 12, 13, 15, 16, 21, and 22, in the following host species: Austrosimulium australense, A. multicorne Tonnoir, and A. tillyardianum, and possibly Chironomus zealandicus Hudson (sites 11 and 15). On South Island the sites were 30, 34, 38, 39, 49, 58, 64, and 67; the hosts included various unidentified species of Chironomidae (including bloodworms and Orthocladiinae) and several species of Simuliidae, including Austrosimulium tillyardianum and A. laticorne. The stonefly host was Zelandoperla fenestrata from site 49.