Monomorphic: species of which only one sex (female) is known to exist.
Monophagous: insects feeding upon only one species or genus of plants.
Monothelious: a union where one female is fecundated by many males.
Monotrocha -ous: Hymenoptera in which the trochanters are single: having legs in which the trochanter is one-jointed.
Monotypical: a genus described from a single species, no other being known; or described from a single specified species with which are associated others believed to be identical in structure: see isotypical and heterotypical.
Moult: a period in the transformation when the larva changes from one instar to another: the cast skin of a larva that has moulted.
Mouth: the anterior opening into the alimentary canal, where the feeding structures are situated and in which the food is prepared for ingestion.
Mouth-parts: a collective name including labrum, mandibles, maxillae, labium and appendages = trophi.
Mucoreus: mouldy: a surface covered with small, fringe-like processes.
Mucro: a long, straight or curved process terminating in a point: the pro-sternal process in Elateridae: the terminal spine or process of an obtect pupa: "the median posterior point of the epigastrium when differentiated by elevation."