 Several species form close relationships with ants, a relationship known as myrmecophily, especially within the family Pyrgodesmidae (Polydesmida), which contains "obligate myrmecophiles", species which have only been found in ant colonies.More species are "facultative myrmecophiles", being non-exclusively associated with ants, including many species of Polyxenida that have been found in ant nests around the world.Many millipede species have commensal relationships with mites of the orders Mesostigmata and Astigmata.