Trichomycetes are fungi and protists living in the guts of arthropods. Herbivorous insects in freshwater habitats commonly house these microbes, and there are over 300 species described. One very common group of aquatic insects occurring in most freshwater systems is caddisflies, belonging to the Order Trichoptera. Although these are potentially good hosts for trichomycetes, there has been little published on trichomycetes in this host and none have been described from caddisflies. We collected and dissected caddisfly larvae from multiple sites in Canada from 2001 to 2018 and describe five new species of trichomycetes from trichopteran larvae. Data are presented on the prevalence and seasonal variation of trichomycetes in caddisfly larvae at one site in Nova Scotia where multi-year collections were made.