[2] Mermithidae are confused with the horsehair worms of the phylum Nematomorpha that have a similar life history and appearance.

[8] The taxonomy of the group has been confused due to poor specimen collection as well as very limited morphological characteristics, and most are discovered by entomologists rather than nematologists.

[9] Mermithid nematodes alter their host's hemolymph osmolality (concentration of salt) to induce water-seeking behavior.

[13][14] An unidentified iridovirus virus has been found in the fly species Culicoides variipennis sonorensis in association with Heleidomermis magnapapula infections.

[11][12][13][15] However, in the case of the interaction between C. v. sonorensis, H. magnapapula, and their iridovirus, the virus appears to kill both host and parasite before they reach maturity, impairing the mermithid's biological control of C. v.