Nematodes

Ants can serve as developmental, definitive, intermediate, or carrier hosts of a variety of nematodes. Parasitic ant nematodes include members of the families Mermithidae, Tetradonematidae, Allantonematidae, Seuratidae, Physalopteridae, Steinernematidae, and Heterorhabditidae. Those nematodes that are phoretically associated with ants, internally or externally, are represented by the Rhabditidae, Diplogastridae, and Panagrolaimidae. Fossils of mermithids, tetradonematids, allantonematids, and diplogastrids associated with ants show the evolutionary history of these relationships, some of which date back to the Eocene (40 mya). (Poinar, 2012)

Pheidole symbiotica
Borowiec and Salata (2015) found that the workers of the previously described species Pheidole symbiotica were simply workers of Pheidole pallidula that were infested with mermithid nematodes.

Sommimyrma symbiotica
Csosz (2012) - Bolton (1988) reported that the holotype of Sommimyrma symbiotica might have been a developmentally abnormal specimen, avoiding any further speculations. According to the images (Figs. 1a, b) probably two or three nematode worms (confirmed by nematologists, Gábor Majoros and George Poinar) nearly completely fill in the gaster of the type individual. The worms are not completely developed; these parasites apparently did not attain the preadult stage. In general characteristics of external morphology the symbiotica holotype specimen is reminiscent of the workers or mermithogenic phenotypes of Myrmica scabrinodis, hence I conducted a PCA based morphometric comparison of the type with both infested and uninfected classes of M. scabrinodis. Results demonstrate that M. symbiotica holotype is nested in the cluster of infested M. scabrinodis individuals (Fig. 2). Based on these results I propose new junior synonymy with M. scabrinodis.