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Key to Monomorium workers of the New World
This key is based on: DuBois, M. B. 1986. A revision of the native New World species of the ant genus Monomorium (minimum group) (Hymenoptera: Formicidae). University of Kansas Science Bulletin. 53:65-119.
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The following species are not included in this key and apparently lack a worker caste: Monomorium inquilinum, Monomorium pergandei, and Monomorium talbotae.
1
- Propodeum rounded; occurs along California coast . . . . . Monomorium ergatogyna
 Head of Monomorium ergatogyna worker |
 Profile of Monomorium ergatogyna worker |
- Propodeum angular . . . . . 2
2
return to couplet #1
- Basal and declivitous faces of propodeum of equal length . . . . . 3
- Basal and declivitous faces of propodeum of unequal length (either face may be longer) . . . . . 5
3
return to couplet #2
- Mesopleuron punctate; fewer than 8 setae projecting above dorsum of alitrunk; occurs throughout central Mexico, Arizona, New Mexico, and parts of Texas . . . . . 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 alitrunk . . . . . 4
4
return to couplet #3
- Petiole and postpetiole convex to flat; occurs in central Mexico . . . . . Monomorium compressum
- Petiole and postpetiole flat to slightly emarginate; occurs throughout Caribbean region . . . . . Monomorium ebeninum
 Head of Monomorium ebeninum worker |
 Profile of Monomorium ebeninum worker |
5
return to couplet #3
- Basal face of propodeum length less than declivity . . . . . 6
- Basal face of propodeum length greater than declivity . . . . . 7
6
return to couplet #5
- Fewer than 6 setae projecting above dorsum of alitrunk; 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 alitrunk; occurs in northern Florida . . . . . Monomorium trageri
 Head of Monomorium trageri worker |
 Profile of Monomorium trageri worker |
7
return to couplet #5
- Mesopleuron punctate; occurs along Atlantic coastline from New Jersey to Florida . . . . . Monomorium viridum
 Head of Monomorium viridum worker |
 Profile of Monomorium viridum worker |
- Mesopleuron not punctate (for further separation of these species refer to their distributions) . . . . . Monomorium minimum . . . . . Monomorium wheelerorum . . . . . Monomorium marjoriae
 Head of Monomorium minimum worker |
 Profile of Monomorium minimum worker |