Key to US Monomorium species

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Key to workers of Monomorium known from the United States and Canada. Monomorium inquilinum, Monomorium pergandei and Monomorium talbotae are not included as they lack the worker caste.


  • Dorsal and posterior faces of propodeum equal in length => 2
  • Dorsal face of propodeum shorter than posterior face => 3
  • Dorsal face of propodeum longer than posterior face => 4


  • Mesopleuron punctate; fewer than 8 setae projecting above dorsum of mesosoma => Monomorium cyaneum
Head of Monomorium cyaneum worker
Profile of Monomorium cyaneum worker
  • Mesopleuron not punctate; more than 10 (rarely 8 or 9) setae projecting above dorsum of mesosoma => Monomorium ebeninum
Head of Monomorium ebeninum worker
Profile of Monomorium ebeninum worker


  • Fewer than 6 setae projecting above dorsum of mesosoma; occurs in northeastern U. S. => Monomorium emarginatum
Head of Monomorium emarginatum worker
Profile of Monomorium emarginatum worker
  • More than 8 setae projecting above dorsum of mesosoma; occurs in northern Florida => Monomorium trageri
Head of Monomorium trageri worker
Profile of Monomorium trageri worker


Head of Monomorium minimum worker
Profile of Monomorium minimum worker
  • Mesopleuron punctate or otherwise sculptured => 5


  • Anterior clypeal margin weakly concave medially, clypeus weakly bicarinate => 6
  • Anterior clypeal margin strongly concave medially, clypeus strongly bicarinate => 7


  • Body uniform yellow with head, mesosoma and anterior section of gaster essentially the same color (posterior section of gaster often dark); petiolar node higher, node narrower, anterior and posterior faces converging only slightly dorsally => Monomorium pharaonis
Head of Monomorium pharaonis worker
Profile of Monomorium pharaonis worker
  • Body strongly bicolored with head and gaster much darker than mesosoma, or occasionally body dark brown and essentially uniformly colored (gaster always uniformly dark); petiolar node lower, node broader, anterior and posterior faces converging more strongly dorsally => Monomorium floricola
Head of Monomorium floricola worker
Profile of Monomorium floricola worker


Head of Monomorium viridum worker
Profile of Monomorium viridum worker
Head of Monomorium ergatogyna worker
Profile of Monomorium ergatogyna worker