Key to Nearctic Strumigenys (as Pyramica)

This worker key is based on: Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028.

Bolton noted in regards to the North American Pyramica species:

Among the endemic North American species, discounting the very derived pergandei group, are two basic dental patterns.

Pattern 1 (clypeata group, ohioensis group, rostrata group): the mandible has 5 teeth in the principal (basal) dental row. Counting from the base tooth 3 is the longest on the margin, distinctly longer than teeth 1 - 2, and much longer than tooth 4. The total dental count is 12.

Pattern 2 (ornata group, pulchella group, talpa group): the mandible has 4 teeth in the principal (basal) dental row. Counting from the base tooth 1 or more usually 2 is the longest on the margin, distinctly longer than tooth 3; tooth 4 is usually also longer than 3. The total dental count is 11.

The second pattern can be derived directly from the first simply by the disappearance of tooth 1 (basal) from the first pattern. This projected loss will also account for the prevalence of longer diastemata between the basal lamella and basal tooth in those groups showing the second pattern, whilst those with the first pattern tend to be adiastemate or have a very short diastema present. Very rarely individual specimens of either dental pattern show a tiny adventitious denticle immediately proximal of the first (basal) tooth on one or both mandibles.

It is most likely that these two dental patterns reflect the most parsimonious grouping of the North American endemics. There is, however, a second major character that has influenced the diagnosis of species groups, the direction of curvature or inclination of main hairs on the leading edge of the scape. In many taxa all main hairs on the scape's leading edge are curved or inclined toward the apex of the scape, but in others there are hairs that are naturally curved or inclined toward the base of the scape.

Another interesting feature of the North American fauna is the strange tendency of many species to evolve hairs on the anterior clypeal margin that curve away from the midline, and sometimes also to develop recurved hairs on the lateral clypeal margins. Outside the Nearctic there is one group, the Afrotropical oxysma group, all of whose members have recurved clypeal hairs, but apart from this the phenomenon is extremely rare. In the North American fauna the presence of such hairs is sometimes a feature of a whole species group (e.g. ornata group), but in several groups it is shown in some species but not others.

Bolton noted in regards to this key:


 * Very rarely individual specimens in series of long-diastemate species may show a minute adventitious denticle immediately proximal of the basalmost tooth; when present this denticle should be ignored at couplet 21.


 * There are some species recorded from Mexico which have not been found in the U.S.A., so species from the extreme south of North America that do not run in this key should also be checked through the Neotropical key.
 * The suspected social parasite Strumigenys inopina, known only from queens and with an unknown host, is omitted from the key.

This key is from a study that included the now synonymized genus Pyramica. Therefore there are two sets of keys for the Strumigenys species from the Nearctic region: the key found below for the group of species once classified as Pyramica and a Key to Neotropical and Nearctic Strumigenys.

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 * Strumigenys

1

 * Mandibles narrow and elongate, sublinear to linear in full-face view; in this view and at full closure the mandibles engage only in the apical third or less of their length, MI 25-67 . . . . . 2


 * Mandibles triangular to elongate-triangular in full-face view; in this view and at full closure the mandibles engage through the apical half or more of their length, at most with a basal gap, MI 11-25 . . . . . 6

2
return to couplet #1
 * Petiole in profile with a conspicuous ventral crest or curtain of spongiform tissue. Disc of postpetiole smooth and shining. MI 25-42 . . . . . 3


 * Petiole in profile without spongiform tissue ventrally. Disc of postpetiole reticulate-punctate. MI 58-67 . . . . . 5

3
return to couplet #2
 * With head in full-face view and mandibles fully closed only 3 teeth visible: 2 small preapical teeth and an extremely long apicodorsal tooth that completely crosses over the tooth from the opposite mandible and projects beyond the outer margin of the opposite mandible. Leading edge of scape with all hairs curved toward the scape apex. Dorsal (outer) surface of hind basitarsus without projecting flagellate hairs. Scape relatively short and head broad, SI < 55, CI 100 or more . . . . . Strumigenys hexamera


 * With head in full-face view and mandibles fully closed numerous small teeth and denticles visible; without an extremely long apicodorsal tooth that completely crosses over the tooth from the opposite mandible and projects beyond the outer margin of the opposite mandible. Leading edge of scape with one or more hairs that are curved toward the scape base. Dorsal (outer) surface of hind basitarsus with 1-3 freely projecting fine flagellate hairs. Scape relatively long and head narrow, SI > 60, CI 68-79 . . . . . 4

4
return to couplet #3
 * Basal and two succeeding teeth on mandible triangular and acute, the second tooth longer than the basal. Disc of postpetiole without posteriorly curved spatulate hairs. Dorsum of mesonotum with a pair of erect simple hairs. Anterior and lateral margins of clypeus meet in angular comers in full-face view. Scape relatively short, SI 65-69. . . . . . Strumigenys angulata


 * Basal and third tooth on mandible triangular and acute, second tooth broad and bluntly rounded; basal longer than second or third teeth. Disc of postpetiole with posteriorly curved spatulate hairs. Dorsum of mesonotum without erect simple hairs. Anterior and lateral margins of clypeus meet through rounded curves in full-face view. Scape relatively long, SI 79-84. . . . . . Strumigenys pergandei

5
return to couplet #2
 * Postpetiole in profile with the ventral spongiform lobe absent or reduced to a minute nonspongiform vestige; lateral lobe absent or represented by a very thin carina of punctulate non-spongiform cuticle. Dorsum of pronotum with a pair of short stiff standing hairs anteriorly between the humeral pair . . . . . Strumigenys eggersi


 * Postpetiole in profile with the ventral spongiform lobe present, small but distinct; lateral lobe present but small, restricted to lower posterior comer of node. Dorsum of pronotum without standing hairs except for the humeral pair. . . . . . Strumigenys gundlachi

6
return to couplet #1
 * Petiole ventrally without trace of spongiform tissue. Pleurae, side of propodeum and disc of postpetiole reticulate-punctate. First gastral tergite finely and densely triolate-punctulate everywhere; first gastral sternite finely shagreenate or punctulate at least basally and laterally. . . . . . Strumigenys margaritae


 * Petiole ventrally with a conspicuous spongiform crest or curtain. Pleurae, side of propodeum and disc of postpetiole smooth. First gastral tergite smooth behind the basigastral costulae, usually entirely smooth but rarely with some sculpture near apex; first gastral sternite unsculptured or with sculpture only near apex . . . . . 7

7
return to couplet #6
 * Clypeus in anterior view with an apicodorsal series of 4-6 stout standing long hairs that radiate from the apex like the ribs of a fan. In profile clypeal dorsum with a pair of very long wire-like hairs that arise at about the midlength; each of these hairs is inclined posteriorly from just above its base, then curves smoothly upwards so that at least the apical half of the shaft is directed vertically or nearly so . . . . . 8


 * Clypeus in anterior view without an apicodorsal series of stout standing long hairs that radiate like the ribs of a fan. In profile clypeal dorsum without long wire-like hairs arising at about the midlength; without hairs that incline posteriorly from just above the base then curve vertically . . . . . 9

8
return to couplet #7
 * Fan of long hairs that radiates from clypeus apicodorsally strongly bulbous at their apices; in profile these bulbous-tipped hairs distinctly curved posteriorly. . . . . . Strumigenys ornata


 * Fan of long hairs that radiates from clypeus apicodorsally simple at their apices; in profile these hairs not obviously curved posteriorly. . . . . . Strumigenys dietrichi

9
return to couplet #7
 * With head in full-face view and mandibles fully closed the masticatory margin without a distinct diastema basally. If basal lamella is concealed by clypeus at full closure then gap between basal tooth and anterior margin of clypeus is shorter than length of basal tooth. If basal lamella is exposed at full closure then diastema between basal tooth and basal lamella is absent or distinctly shorter than length of basal tooth . . . . . 10


 * With head in full-face view and mandibles fully closed the masticatory margin with a distinct diastema basally. If basal lamella is concealed by clypeus at full closure then gap between basal tooth and anterior margin of clypeus is greater than length of basal tooth. If basal lamella is exposed at full closure then diastema between basal tooth and basal lamella is distinctly longer than length of basal tooth . . . . . 21

10
return to couplet #9
 * Dorsal surface of fully closed mandible basally with a very distinct sharp transverse edge or rim running across the width of the blade, parallel to and in front of the anterior clypeal margin. Pronotum sharply marginate dorsolaterally, the dorsum transversely flattened and unsculptured. First gastral tergite without standing hairs of any form. (Cosmopolitan tramp species) . . . . . Strumigenys membranifera


 * Dorsal surface of fully closed mandible basally without a transverse edge or rim running across the width of the blade parallel to the anterior clypeal margin. Pronotum not marginate dorsolaterally, the dorsum transversely convex and sculptured. First gastral tergite with standing hairs of some form present. . . . . . 11

11
return to couplet #10
 * With head in full-face view hairs that project from the lateral clypeal margin fine, conspicuously J-shaped and curved posteriorly. . . . . . Strumigenys ohioensis


 * With head in full-face view hairs that project from the lateral clypeal margin variable in form but not J-shaped and curved or inclined anteriorly . . . . . 12

12
return to couplet #11
 * Leading edge of scape with a row of conspicuous projecting curved hairs of which one or more, distal to the subbasal bend, distinctly curves toward the base of the scape . . . . . 13


 * Leading edge of scape with all projecting hairs curved toward the apex of the scape; entirely lacking hairs that curve toward the base of the scape . . . . . 17

13
return to couplet #12
 * Apical portion of first gastral tergite subopaque, densely sculptured with fine reticulation and striolation; same area on first gastral sternite similarly sculptured. Propodeal dorsum predominantly smooth and shining. . . . . . Strumigenys californica


 * Apical portions of first gastral tergite and sternite smooth and shining, without reticulate or striolate sculpture. Propodeal dorsum punctate to reticulate-punctate . . . . . 14

14
return to couplet #13
 * Basal lamella of mandible followed immediately by a row of 7 coarse conical teeth, without trace of a diastema. Anterior clypeal margin shallowly concave. Dorsum of head close to occipital margin with a transverse row of 4 hairs that are differentiated from the ground-pilosity, being longer, more erect and more slender. With head in full-face view an apicoscrobal hair present, stout simple and curved anteriorly. . . . . . Strumigenys rostrata


 * Basal lamella of mandible followed by a small diastema (distinctly shorter than length of basal tooth), distal to which is a row of 5 small acute teeth. Anterior clypeal margin transverse to shallowly convex. Dorsum of head close to occipital margin without slender hairs that are differentiated from the ground-pilosity. With head in full-face view apicoscrobal hair absent. . . . . . 15

15
return to couplet #14
 * Lateral spongiform lobe of postpetiole massive, in profile its area distinctly greater than that of the exposed cuticle of the disc. In dorsal view postpetiole disc with sides thickly surrounded by spongiform tissue; maximum width across the spongiform tissue almost twice the diameter of the disc. Maximum depth of ventral spongiform curtain of petiole deeper than height of peduncle . . . . . 16


 * Lateral spongiform lobe of postpetiole small, in profile its area less than that of the exposed cuticle of the disc. In dorsal view postpetiole disc with sides only very thinly margined by spongiform tissue; maximum width across the spongiform tissue only ca. 1. 3 times the diameter of the disc. Maximum depth of ventral spongiform curtain of petiole narrower than height of peduncle. . . . . . Strumigenys arizonica

16
return to couplet #15
 * Mesonotum without a pair of long flagellate hairs. Dorsum of pronotum and mesonotum evenly reticulate-punctate, sculpture on the two not contrasting. Pronotum without a median longitudinal carina. MI 16-20, CI 64-69. . . . . . Strumigenys bunki


 * Mesonotum with a pair of long flagellate hairs. Dorsum of pronotum indistinctly shallowly striolate, mesonotum reticulate-punctate, the two contrasting. Pronotum with a median longitudinal carina. MI 22-25, CI 71-75. . . . . . Strumigenys carolinensis

17
return to couplet #12
 * With head in full-face view and mandibles fully closed the basal lamella mostly exposed, occupying at least the basal third of the exposed length of the margin; exposed length of basal lamella at least equal to length of margin occupied by the basal 4 teeth together. On mandible second tooth from base the longest. . . . . . Strumigenys archboldi


 * With head in full-face view and mandibles fully closed the basal lamella mostly or entirely concealed, occupying at most the extreme base of the exposed length of the margin; exposed length of basal lamella far less than length of margin occupied by the basal 4 teeth together. On mandible third tooth from base the longest. . . . . . 18

18
return to couplet #17
 * Dorsum of clypeus with dense short broadly oval-spatulate to scale-like hairs; in profile these hairs reclinate to appressed. In full-face view hairs that project from the lateral clypeal outline either scale-like and appressed to the margin or broadly spatulate and strongly curved anteriorly . . . . . 19


 * Dorsum of clypeus with elongate narrow hairs that are simple, somewhat flattened or very narrowly linear-spatulate; in profile these hairs not appressed, either elevated and inclined anteriorly or curving anteriorly in their apical halves. In full-face view hairs that project from the lateral clypeal outline either fine and simple or narrow and linear-spatulate, inclined anteriorly, only very weakly curved or more or less straight. . . . . . 20

19
return to couplet #17
 * With head in full-face view hairs on lateral clypeal margin project and are curved anteriorly, not appressed to the surface, distinctly longer and broader than the hairs on the clypeal dorsum. Upper scrobe margin with 1-2 laterally projecting long flagellate hairs. In profile flagellate hairs present on cephalic dorsum behind highest point of vertex. . . . . . Strumigenys clypeata


 * With head in full-face view hairs on lateral clypeal margin scale-like and closely appressed to the surface, no longer or broader than the hairs on the clypeal dorsum. Upper scrobe margin without flagellate hairs. In profile cephalic dorsum without flagellate hairs. . . . . . Strumigenys rohweri

20
return to couplet #17
 * Clypeal pilosity everywhere very fine and filiform, acute apically. In full-face view hairs that project from lateral margin of clypeus the same shape and about the same length as-those arising mid-dorsally. In profile hairs on clypeal mid-dorsum elevated and inclined anteriorly. . . . . . Strumigenys laevinasis


 * Clypeal pilosity everywhere narrowly linear-spatulate or flattened and spatulate in the apical half and truncated apically. In full-face view hairs that project from lateral margin of clypeus of different shape and longer than those arising mid-dorsally. In profile hairs on clypeal mid-dorsum curved or arched anteriorly. . . . . . Strumigenys pilinasis

21
return to couplet #9
 * Principal basal dental row of mandible with 5 teeth followed distally by 2 smaller teeth; counting from the base tooth 3 the longest . . . . . 22


 * Principal basal dental row of mandible with 4 teeth followed distally by 2 smaller teeth; counting from the base tooth 3 not the longest . . . . . 27

22
return to couplet #21
 * Clypeal margin anteriorly and laterally with a continuous broad groove around the periphery. In profile the clypeal edge with a distinct dorsal border and a more strongly prominent ventral border, the two separated by the evenly concave peripheral groove. In full-face view both borders visible and concentric as the lower projects beyond the upper . . . . . 23


 * Clypeal margin anteriorly and laterally without a continuous groove around the periphery. In profile the clypeal edge thick or thin but single, without upper and lower borders separated by a concave peripheral groove. In full-face view the margin simple, without two visible concentric borders . . . . . 24

23
return to couplet #22
 * With clypeus in profile a very long erect flagellate hair arises from the dorsum just in front of the antennal socket; this hair much longer than any others on the dorsum. Dorsolateral margin of head with 2 pairs of flagellate hairs and cephalic dorsum with a flagellate pair close to the occipital margin. . . . . . Strumigenys filirrhina


 * With clypeus in profile the dorsum with short curved non-flagellate hairs only, without a very long erect flagellate hair arising just in front of the antennal socket. Dorsolateral margin and dorsum of head without flagellate hairs. . . . . . Strumigenys bimarginata

24
return to couplet #22
 * Hairs on dorsum and margins of clypeus all very fine, filiform and acute apically; clypeus entirely lacking spatulate or spoon-shaped hairs. . . . . . Strumigenys reliquia


 * Hairs on dorsum and margins of clypeus mostly or entirely spatulate or spoon-shaped; clypeus entirely lacking fine filiform hairs . . . . . 25

25
return to couplet #24
 * All hairs on leading edge of scape curved or inclined toward the apex of the scape. Upper scrobe margin with 2-3 laterally projecting long flagellate hairs, one apicoscrobal and 1-2 anterior to this. . . . . . Strumigenys clypeata


 * Two or more hairs on leading edge of scape curved toward the base of the scape. Upper scrobe margin with a single laterally projecting long flagellate hair, in apicoscrobal position . . . . . 26

26
return to couplet #25
 * First (basal) tooth on mandible distinctly shorter than second. Clypeal dorsum with short spatulate hairs that are not translucent. With gaster in dorsal view longest basigastral costulae posterior to line of limbus at least as long as postpetiole disc and mostly longer . . . . . Strumigenys chiricahua


 * First (basal) tooth on mandible distinctly longer than second. Clypeal dorsum with fully translucent large spoon-shaped hairs. With gaster in dorsal view longest basigastral costulae posterior to line of limbus much shorter than postpetiole disc. . . . . . Strumigenys hyalina

27
return to couplet #21
 * Leading edge of scape with two or more of the principal hairs curved or inclined toward the base of the scape . . . . . 28


 * Leading edge of scape with all hairs curved or inclined toward the apex of the scape . . . . . 37

28
return to couplet #27
 * All hairs on clypeus, including those on margins as well as those on dorsum, very fine, slender and simple, acute apically. . . . . . Strumigenys filitalpa


 * Some or all clypeal hairs spatulate, clavate, spoon-shaped or otherwise bizarre; clypeal hairs not entirely very fine slender and simple . . . . . 29

29
return to couplet #28
 * In full-face view hairs on lateral clypeal margin curved anteriorly and hairs on anterior clypeal margin either curved toward the midline or directed anteriorly. Entirety of clypeal margin without any hairs that are curved away from the midline, inclined or curved outwards, or curved posterolaterally . . . . . 30


 * In full-face view at least one pair of hairs on clypeal margin curved away from the midline, or inclined or curved outward, or curved posterolaterally. Hairs so oriented may occur on lateral margins but at least a single pair, on the anterior margin close to midline, curved away from the midline . . . . . 33

30
return to couplet #29
 * Pronotal humeral hair absent. With head in full-face view upper scrobe margin without a laterally projecting elongate filiform or flagellate hair. . . . . . Strumigenys creightoni


 * Pronotal humeral hair present, filiform or flagellate. With head in full-face view upper scrobe margin usually with a laterally projecting filiform or flagellate hair just behind level of eye or close to apex of scrobe . . . . . 31

31
return to couplet #30
 * With head in full-face view entire dorsum of clypeus densely clothed with very conspicuous broadly spatulate hairs, those located mid-dorsally only slightly shorter and narrower than those that fringe the lateral clypeal margin. Slightly larger species, HW 0.40-0.43. . . . . . Strumigenys abdita


 * With head in full-face view dorsum of clypeus equipped with small narrowly spatulate hairs, those located mid-dorsally tiny, much smaller and narrower than the large curved hairs that fringe the lateral clypeal margin. Slightly smaller species, HW 0.33-0.38 . . . . . 32

32
return to couplet #31
 * Pair of standing long hairs on dorsum of pronotum, pair on mesonotum and hairs on first gastral tergite filiform and feebly curved, not flagellate. With petiole in profile maximum depth of ventral spongiform curtain less than maximum depth of peduncle. Head slightly broader, CI 69-74 . . . . . Strumigenys metazytes


 * Pair of standing long hairs on dorsum of pronotum, pair on mesonotum and hairs on first gastral tergite distinctly flagellate. With petiole in profile maximum depth of ventral spongiform curtain greater than maximum depth of peduncle. Head slightly narrower, CI 63-65 . . . . . Strumigenys deyrupi

33
return to couplet #29
 * Pronotal humeral hair present. Dorsal (outer) surface of hind tibia, basitarsus, or both with 1-2 long fine flagellate hairs; tibia without suberect hairs . . . . . 34


 * Pronotal humeral hair absent. Dorsal (outer) surface of hind tibia and basitarsus without long fine flagellate hairs; tibia with short suberect hairs . . . . . Strumigenys memorialis

34
return to couplet #33
 * With clypeus in full-face view laterally or posteriorly curved marginal hairs restricted to 1-2 pairs situated on the anterior margin above the mandibles; hairs on lateral margins not all curved posteriorly . . . . . 35


 * With clypeus in full-face view laterally or posteriorly curved marginal hairs present on the anterior margin above the mandibles; all hairs posteriorly curved on the lateral margins. . . . . . Strumigenys reflexa

35
return to couplet #34
 * Hairs that project from lateral margin of clypeus thick and simple, sparse, not strongly curved anteriorly nor forming a regular fringe. With head in full-face view clypeus slightly longer than broad; with mandibles fully closed the lateral clypeal margin continuing the line of the outer margin of the mandible . . . . . Strumigenys cloydi


 * Hairs that project from lateral margin of clypeus broadly spatulate to spoon-shaped, most or all strongly curved anteriorly, usually forming a regular fringe. With head in full-face view clypeus distinctly broader than long; with mandibles fully closed the lateral clypeal margin extending far outside the line of the outer margin of the mandible . . . . . 36

36
return to couplet #35
 * With head in full-face view a flagellate apicoscrobal hair absent. Pronotal humeral hair simple, stiff and stout. Mesonotum with erect stout simple hairs. Head broader and scapes shorter, CI 68-72, SI 69-75. . . . . . Strumigenys missouriensis


 * With head in full-face view a flagellate apicoscrobal hair present. Pronotal humeral hair flagellate, elongate and fine. Mesonotum with a single pair of erect fine flagellate hairs. Head narrower and scapes longer, CI 61-66, SI 78-82. . . . . . Strumigenys pulchella

37
return to couplet #27
 * Some or all hairs on dorsum of clypeus curved or inclined posteriorly or posterolaterally . . . . . 38


 * All hairs on dorsum of clypeus curved or inclined anteriorly or anterolaterally . . . . . 39

38
return to couplet #37
 * Lateral clypeal margin with obviously spatulate or spoon-shaped curved hairs. With head in full-face view clypeus broader than long; with mandibles fully closed the lateral clypeal margin extending well beyond the the line of the outer margin of the mandible. Anterior tip of clypeus not curving upward away from the dorsal surface of the mandible. CI 66-70, SI 70-74. . . . . . Strumigenys wrayi


 * Lateral clypeal margin with stiff elongate hairs that are thickened apically but obviously are not spatulate or spoon-shaped. With head in full-face view clypeus slightly longer than broad; with mandibles fully closed the lateral clypeal margin continuing the line of the outer margin of the mandible. Anterior tip of clypeus feebly curving upward away from the dorsal surface of the mandible. CI 60-64, SI 79-83.  . . . . . Strumigenys cloydi

39
return to couplet #37
 * Dorsolateral margin of head with a single freely projecting long flagellate hair. Anteriorly curved hairs that fringe the lateral clypeal margins strong, linear-spatulate to weakly spoon-shaped. Hairs on clypeal dorsum spatulate. . . . . . Strumigenys talpa


 * Dorsolateral margin of head with two freely projecting long flagellate hairs. Anteriorly curved hairs that fringe the lateral clypeal margins very soft and weak, filiform. Hairs on clypeal dorsum very slender, simple and acute. . . . . . Strumigenys filitalpa