Myrmicinosporidium durum is an entomopathogenic fungus in the phylum Blastocladiomycota. It infects many ant species and is distributed almost globally.
Karl Hölldobler described Myrmicinosporidium durum from infected ants of the species Leptothorax tuberum in Wurzburg, Germany.
Subsequent research confirmed the fungal nature of the infection and suggested a relationship with Coelomomyces in the Chytridiomycetes.
In 2021, Gorczak and Trigos-Peral demonstrated using rDNA markers from infected Solenopsis fugax workers that M. durum belongs to Blastocladiomycota.
Myrmicinosporidium durum is normally detected because of its dark thick-walled spores that develop in large numbers inside the insect's hemocoel and that can be seen through the cuticle. Hyphae and mycelium were not seen before 1993.
Myrmicinosporidium durum has been recorded from many European countries, North America and Australia.