Key to North American Genera of Myrmicinae

This key to the genera of North American Myrmicinae has been adapted/modified from Fisher & Cover (2007).

1

 * Antenna with four or six segments, last two segments forming distinct club (A) => Strumigenys
 * Antenna with seven segments, last two segments forming distinct club (AA). (Not commonly collected, Florida.) => Eurhopalothrix
 * Antenna with 10 segments, last two segments forming distinct club (AAA) => Solenopsis
 * Antenna with 11 segments, apical club variable => 2
 * Antenna with 12 segments, apical club variable (AAAA) => 19

2

 * Postpetiole attached to dorsal surface of following abdominal segment 4 (A) and capable of flexing upwards over dorsal surface of body. Petiole strongly flattened and lacking dorsal node (B) => Crematogaster
 * Postpetiole attached to anterior face of following abdominal segment 4 (AA) and not capable of flexing upwards over dorsal surface of body. Petiole nearly always with distinct dorsal node (BB). If node absent (Xenomyrmex), petiole not strongly flattened => 3



3

 * With head in side view, a sharply differentiated diagonal carina (ridge) present, extending up from mandible insertions to above the eye (A). Antennal club often absent (B). Head and body often with tubercles or spines (C) => 4
 * With head in side view, lacking diagonal carina running from the mandible insertions to above the eye (AA), though longitudinal rugae may be present on sides and front of head. Antenna often with a 2- or 3-segmented club (BB). Head and body usually lacking tubercles, but spines or teeth may be present (CC) => 8



4

 * Frontal lobes massively expanded laterally, in full-face view covering most of the sides of the head below the eye (A). Head and body with flattened and appressed hairs; erect hairs absent. Tergite of abdominal segment 4 without tubercles (B) => Cyphomyrmex
 * Frontal lobes not expanded laterally to cover the sides of the head (AA). Head and body with conspicuous erect hairs or setae, often stiff and curled. Abdominal tergite 4 sometimes tuberculate (BB) => 5

5

 * Frontal lobes enlarged and reaching anterior margin of clypeus in full-face view (A). Small, monomorphic species lacking spines, teeth, or prominent tubercles on mesosoma, except for two small teeth on the humeral angles, and two on the propodeum (B). (Central Texas to Louisiana.) => Mycetosoritis
 * Frontal lobes variously shaped, but not reaching anterior margin of clypeus in full-face view (AA). Conspicuous spines or tubercles on mesosomal dorsum (BB). Workers sometimes polymorphic => 6

6

 * Dorsum of mesosoma with three pairs of long spines (A) and without tubercles. Vertex and abdominal tergite 4 more or less smooth and without tubercles (B). Strongly polymorphic => Atta
 * Dorsum of mesosoma with more than three pairs of long spines or with tubercles (AA). Vertex and abdominal tergite 4 usually roughened and tuberculate (BB). Monomorphic or moderately polymorphic => 7

7

 * Mesosomal spines generally absent, tuberculate if present (A). Frontal carinae present and extending almost to the posterior corners of the head (B). Entire head and mesosoma with at least some, often many, small tubercles (C), which are blunt or sometimes bear short, sharp teeth. Monomorphic or very weakly polymorphic => Trachymyrmex
 * Mesosomal spines present, prominent, never tuberculate (AA). Frontal carinae indistinct and ending well in front of the posterior corners of the head (BB). On head and mesosoma, tubercles limited largely to the tops of the occipital margin and dorsum of mesosoma (BB). Moderately polymorphic. (Western Texas to southern California.) => Acromyrmex



8

 * Frontal carinae expanded to cover the sides of the head in full-face view (A). Antennal scrobes deep, receiving entire scape (A). Dorsum of mesosoma strongly flattened; promesonotum sharply marginate at side, often spinose (B). Dimorphic or polymorphic => Cephalotes
 * Frontal carinae not greatly expanded to cover the sides of the head in full-face view (AA). Antennal scrobes, when present, shallow and not receiving entire scape (AA). Promesonotum not laterally marginate or spinose (BB). Monomorphic, except for one rare, minute species => 9

9

 * Petiolar node absent or rudimentary (A) and propodeum rounded in profile without spines or teeth (B). (Southern Florida.) => Xenomyrmex
 * Petiolar node nearly always present and well developed (AA); if absent, then propodeum with spines or teeth (BB) => 10

10

 * Antennal club clearly 2-segmented (A) => 11
 * Antennal club 3-segmented (AA), absent, or indistinct => 12

11

 * Frontal carinae present, extending well past the eye, almost to the occipital margin (A). Propodeum with a pair of long spines (B). Eye with more than 10 facets (C); lower margin of eye flat. (Southern Florida.) => Wasmannia
 * Frontal carinae absent (AA). Propodeum armed with a pair of short teeth (BB). Eye minute, with five or fewer facets (CC); lower margin of eye rounded. Dimorphic with major and minor workers; majors not yet recorded in North America. (Central Texas.) => Carebara

12

 * Frontal carinae extending well past the eye, sometimes to the occipital margin (A) => 13
 * Frontal carinae ending far short of occipital margin, seldom surpassing the eye (AA) => 15

13

 * Dorsum of head and mesosoma rugoreticulate. Mandible with six or seven teeth (A). Area of clypeus immediately in front of antennal sockets raised up into a narrow ridge or shield wall so that sockets appear to be placed within deep pits (B). Antennal scapes not flattened at base => Tetramorium
 * Mandible with either zero or four teeth (AA). Area of clypeus immediately in front of antennal sockets flat and not raised up into a narrow ridge or shield wall; antennal sockets not appearing to be set within deep pits (BB). Antennal scapes flattened at base => 14

14

 * Mandible with a broad cutting margin, but no discernible teeth. Anterior edge of clypeus with prominent median notch or deep concavity (A). (Eastern Canada, northeastern U.S.) => Harpagoxenus
 * Mandible with four teeth. Median impression of anterior margin of clypeus broad and very shallow (AA). (Eastern North America.) => Temnothorax

15

 * Eye rudimentary or absent. Mandible with four teeth and strongly oblique cutting margin. Propodeum rounded in profile (A). (Not commonly collected, known from southern Arizona, New Mexico, and California.) => Dolopomyrmex
 * Eye present, often with 10 or more facets. Mandible subtriangular, with more than four teeth. Propodeum usually with teeth or spines (AA), sometimes just angulate at juncture of dorsal and posterior faces => 16

16

 * Eyes with short, erect hairs (A) (use high magnification) => Formicoxenus
 * Eyes lacking erect hairs => 17

17

 * Dorsal surface of petiole node armed with one or more pairs of short spines or tubercles (A). (Known from Rio Grande valley near Brownsville, Texas.) => Nesomyrmex
 * Dorsal surface of petiole node unarmed, without a pair of short spines or tubercles => 18

18

 * Mandible with six teeth (A). Usually, median portion of clypeus smooth and longitudinally excavate, lacking carinae centrally; several carinae usually present on lateral portions (B) => Leptothorax
 * Mandible with five teeth (AA). Median portion of clypeus more or less flat, not smooth and longitudinally excavate, and with one or more carinae centrally, sometimes weakly developed or very rarely absent; carinae on lateral portions often present (BB) => Temnothorax

19

 * Petiole short and subcylindrical to subquadrate, without anterior peduncle and with dorsal node absent or rudimentary (A). Propodeum with two pairs of teeth: a short pair of teeth anterior to a longer pair on the propodeal angle (B). In side view, the ventral margin of the head with a sharp longitudinal carina below the eye, extending from base of mandible to posterior corner of head (C). Pronotal humeri angulate => Myrmecina
 * Petiole with distinct dorsal node (AA). Propodeum unarmed or armed with a single pair of spines or denticles (BB). Carina as described above absent (CC). Pronotal humeri rounded, rarely subangulate => 20

20

 * Petiole with a large, anteroventral, plate-like process (A). Anterior peduncle absent (B). (District of Columbia and adjacent Maryland.) => Vollenhovia
 * Plate-like, subpetiolar process as described above absent; a small anteroventral tooth may be present (AA). Petiole often with a distinct peduncle (BB); sometimes reduced or absent (BBB) => 21

21

 * Area of clypeus immediately in front of antennal sockets raised up into a narrow ridge or shield wall so that sockets appear to be placed within deep pits (A). Middle and hind tibial spurs simple or absent (B) (use high magnification, 50 to 100 x). In side view, dorsal node of petiole rounded or subquadrate (C). (Mainly urban areas.) => Tetramorium
 * Area of clypeus immediately in front of antennal sockets usually flat and not raised up into a narrow ridge or shield wall; thus, antennal sockets do not appear to be set within deep pits (AA). If narrow ridge appears to be present (AAA), then middle and hind tibial spurs pectinate (use high magnification, 50 to 100 x) (BB) and dorsal node of petiole more or less triangular in side view (CC) => 22

22

 * Combining the following: In dorsal view, postpetiole subcircular and notably swollen relative to the petiole (A). Dorsum of head and mesosoma very finely sculptured, dull and lacking erect hairs. Clypeus with long median seta that projects forward over the mandibles (B) => Cardiocondyla
 * Not as above: postpetiole variable in shape and size, but not both subcircular and notably swollen relative to the petiole in dorsal view (AA). Sculpture on dorsum of head and/or mesosoma, when present, often including rugae or punctures; erect hairs usually present on dorsum of head and mesosoma. Median clypeal seta sometimes absent (BB) => 23

23

 * Psammophore (long, curved hairs on underside of head) present (A). Mesosoma in side view weakly to moderately convex; metanotal impression absent or indistinct (B). Petiolar peduncle well developed, mostly smooth and strongly shiny. Petiolar node usually has a short, often nearly vertical anterior face that meets the long, gradually sloping posterior face to form a sharp (sometimes rounded) peak, giving the node a triangular shape overall (C) => Pogonomyrmex
 * Psammophore generally absent. Mesosomal profile variable, but if psammophore present, then propodeum depressed below level of mesonotum in side view (BB). Other characters variable => 24

24

 * Combining the following: Anteromedian portion of clypeus notably elevated and bicarinate (carinae usually ending to form two submedian teeth on the anterior clypeal margin) (A). Propodeum rounded or rarely angular, unarmed, without spines or teeth (B). Antennal club 3-segmented (C) => 25
 * Clypeus generally not bicarinate; if so (AA), propodeum usually armed with teeth or short spines (BB). Antennal club variable (CC), sometimes absent => 26



25

 * Apical segment of antenna longer than next 2 segments, second segment longer and broader than third segment. Clypeus smooth or bicarinate. Anterior clypeal lobe same width or narrower than antennal insertions. Dorsum of propodeum smooth, reticulate-punctate or sometimes otherwise, but never transversely striate or costulate => Monomorium
 * Apical segment of antenna similar in length to next 2 segments, second segment same length and diameter as third segment. Clypeus smooth. Anterior clypeal lobe wider than antennal insertions. Dorsum of propodeum transversely striate or costulate, even if only faintly so. (Rare, Florida.) => Trichomyrmex

26

 * Propodeum depressed below level of promesonotum in side view (A) and/or metanotal impression substantial (B), separating promesonotum and propodeum into separate, evenly rounded convexities => 27
 * Propodeum not depressed below level of promesonotum (AA). Metanotal impression often absent, or slight when present, just briefly interrupting the mesosomal profile => 34

27

 * Propodeum slightly depressed below level of pro mesonotum (A) and antennal sockets widely separated by the median posterior portion of the clypeus, which forms a broadly rounded or triangular shape (B). Metanotal impression sometimes substantial (C), separating promeso notum and propodeum into separate, evenly rounded convexities => 28
 * Propodeum usually notably depressed below level of promesonotum (AA); if only slightly depressed, then antennal sockets closely approximated, with the median posterior portion of the clypeus forming a narrow, finger-like lobe (BB). Metanotal impression variable. Dorsal surface of propodeum often flattened (AA), but sometimes convex => 30

28

 * Mandible with five teeth (A). Middle and hind tibial spurs simple (B). Propodeum armed with short teeth (C) => Temnothorax
 * Mandible with seven or more teeth (AA). Middle and hind tibial spurs pectinate (use high magnification, 50 to 100 x) (BB). Propodeum with teeth or spines (CC) or unarmed (CCC) => 29

29

 * Propodeum unarmed (A) => Manica
 * Propodeum with teeth or spines (AA) => Myrmica

30

 * Antennal sockets closely approximated; thus, median posterior portion of clypeus forms a narrow, finger-like projection that extends rearwards between the frontal lobes (A). Anterior median portion of clypeus often with a pair of fine, longitudinal carinae that diverge anteriorly (B) => Stenamma
 * Antennal sockets not closely approximated (AA), the median posterior portion of the clypeus forming a triangular or broadly rounded shape extending rearwards between the frontal lobes. Clypeus never bicarinate (BB) => 31

31

 * Antenna with a distinct 3- or (rarely) 4-segmented apical club (A). Palp count 3,2 or 2,2. Worker caste dimorphic, rarely strongly polymorphic => Pheidole
 * Antenna without distinct apical club (AA). Palp count 5,3 or 4,3. Workers monomorphic or weakly to moderately polymorphic => 32

32

 * Head quadrate (A). Mandible short and thick, with outer margin strongly curving toward the midline (B). Psammophore often present => Veromessor
 * Head longer than broad, often noticeably narrowed toward the vertex (AA). Mandible slender and triangular, with outer margin not strongly curving toward midline (BB). Psammophore absent => 33

33

 * Body smaller, total length rarely over 7 mm (head width and length each less than 2mm, intraocular distance less than 1.4mm, distance between tips of spines less than 0.56mm and spine length less than 1mm, Weber’s length less than 3mm). Frontal triangle smooth or punctate. Mesopropodeal suture clearly marked on dorsum of mesosoma. Propodeal spines often short and poorly developed, may be absent. Postpetiole constricted at connection to gaster. Most common in mesic sites => Aphaenogaster
 * Body larger, total length usually at least 8 mm (head width and length each greater than 2mm, intraocular distance 1.4mm or greater, distance between tips of spines greater than 0.56mm and spine length 1mm or longer, Weber’s length 3mm or greater). Frontal triangle striate. Metanotal suture poorly marked on dorsum of mesosoma. Propodeal spines long and sharp. Postpetiole not constricted at connection to gaster. Most common in arid and semi-arid sites => Novomessor

34

 * Metanotal impression small but present, interrupting the mesosomal profile in side view as a modest notch or indentation (A) => 35
 * Metanotal impression absent (AA); mesosomal profile without interruption, evenly convex or flattened, or very slightly undulating => 36

35

 * Antennal sockets closely approximated; median posterior portion of clypeus forming a narrow, finger-like lobe extending rearwards between the two frontal lobes (A). Tibial spur simple (B). Antennal scape gradually and evenly bent as it approaches the insertion (C) => Stenamma
 * Antennal sockets not closely approximated; median posterior portion of clypeus forming a triangular or broadly rounded shape extending rearwards between the frontal lobes (AA). Tibial spur pectinate (BB). Antennal scape often sharply bent near insertion; the bend frequently features a conspicuous ridge or lamina (CC) => Myrmica



36

 * Antennal sockets closely approximated; median posterior portion of clypeus forming a narrow, finger-like lobe extending rearwards between the two frontal lobes (A). Clypeus bicarinate, with the carinae often small (use high magnification), and sometimes not extending to the anterior margin (B). Eyes very small (less than 15 facets, usually less than 10) => Rogeria
 * Antennal sockets not closely approximated; median portion of clypeus forming a triangular or broadly rounded shape extending rearwards between the frontal lobes (AA). Clypeus never bicarinate (BB). Eyes well developed, generally moderate to large in size (more than 15 facets) => 37

37

 * Mandible with more than five teeth (A). Antennal club absent (B). Head and mesosomal dorsum covered with dense rugo-reticulate sculpture (C) => Pogonomyrmex
 * Mandible with five teeth (AA). Antennal club 3-segmented (BB). Sculpture on head and mesosoma variable, seldom rugo-reticulate on both head and mesosomal dorsum (CC) => Temnothorax