As previously mentioned, mermithids are generally specific to one or a few species of insects and are rarely found in other insects. As a result, little concern has been shown for potential danger of these parasites to mammals. To date, only limited mammalian safety studies have been made. Ignoffo et al. (1974) reported that when suckling and adult mice and adult rats were subjected to either per os, intranasal, intraperitoneal, or dermal challenge of R. culicivorax, their body weight gain and histologies were identical to those of untreated animals. Immunodepressed rats also were not susceptible. Similar findings were reported for R. iyengari in India (Anonymous, 1978). Similarly, studies in the People's Republic of China showed that no pathology was apparent in dermally challenged suckling mice, in orally exposed adult rats, or in three species of fish when exposed to R. jingdeensis (Anonymous, 1982).

Mermithids have occasionally been reported as accidental parasites of man. Poinar (1979) reviewed all such cases in the literature and concluded that in most cases the data were insufficient to ascertain if human parasitism actually occurred. He further concluded that the question of accidental human infection by mermithids cannot be definitely answered at this time and should only be accepted as fact when proven experimentally or when parasites are found developing in situ in the human organism. Further, the Environmental Protection Agency (United States) has exempted mermithids from safety regulations.