 The host association between Myrmecia and eucharitid wasps began several million years ago; M. forficata larvae are the host to Austeucharis myrmeciae, being the first recorded eucharitid parasitoid of an ant, and Austeucharis fasciiventris is a parasitoid to M. gulosa pupae. M. pilosula is affected by a gregarines parasite that changes an ants colour from their typical black appearance to brown. This was discovered when brown workers were dissected and found to have gregarinasina spores, while black workers showed no spores. Another unidentified gregarine parasite is known to infect the larvae of M. pilosula and other Myrmecia species. This gregarine parasite also softens the ant's cuticle. Other parasites include Beauveria bassiana, Paecilomyces lilacinus, Chalcura affinis, Tricoryna wasps, and various mermithid nematodes.
