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Key to Strumigenys worker species in or possible in the southeastern United States (from Bolton 2000; Deyrup and Lubertazzi 2001 and Deyrup and Cover 1999)

Notes: 

In a recent paper by Baroni Urbani and de Andrade (2007), Pyramica was synonymized with Strumigenys, and therefore the name Pyramica is no longer valid. However, there was some debate as to the methodology used in their paper as compared to Bolton (2000). It finally appears that other researchers have come to the same conclusion as Baroni Urbani and de Andrade, and therefore, I have finally gotten around to changing the names on this web site. With this treatment, the genus Strumigenys is huge! Obvious species groups and likely generic groups are included in this once again massive genus, and I suspect, it will be just a matter of time before it is split up into several genera.

When hairs that arise on the lateral margins of the clypeus are described as curving either posteriorly or anteriorly, posteriorly indicates that they curve in a direction toward the occiput and anteriorly indicates they curve toward the mandibles. 

1        

In full face view mandibles elongate and narrowed, sublinear to linear and when fully closed the mandibles engage only in the apical third or less of their length (MI 25-67)

...2
  In full face view mandibles triangular to elongate-triangular, and when fully closed the mandibles engage through the apical half or more of their length, with a basal gap at most (MI 11-25)
...14
2(1)     Antennae with 4 segments, the first funicular segment followed immediately by the two segmented club (FL)
  Antennae usually with 5 or 6 segments
...3
3(2) Mandibles extremely long and narrow, almost as long as head length
...4
  Mandibles elongate, but length not approaching the length of head
...12
4(3) Leading edge of scape with all hairs curved toward apex of scape
...5
  Leading edge of scape with one to many hairs that distinctly curve toward base of scape
...7
5(4) Entire body, including head, with numerous long, fine, flagellate hairs that give an almost "whooly" appearance to this species
  Head and body lacking elongate, fine, flagellate hairs; instead with erect spatulate to slighty forked hairs
...6
6(5) Mandible with two stout preapical teeth; entire side of mesopleura and waist lacking sculpture, shiny
  Mandible lacking preapical teeth; entire side of mesosoma and waist with reticulate sculpture
7(4) Postpetiole, in profile, with ventral spongiform lobe absent or reduced
  Postpetiole, in profile, with ventral spongiform lobe present
...8
8(7) At least 4 evenly spaced small teeth or denticles of approximately the same size present along inner border of apical third of mandible
  Mandible lacking small teeth on inner border, or with only one or two teeth; if present, first tooth from the apex longer than other tooth
...9
9(8)

Mandible without intercalary teeth or denticles between apicodorsal and apicoventral teeth of the apical fork or at dorsal base of apicoventral tooth (also keys later, sometimes has denticles between apicodorsal and apicoventral teeth)
  Mandible with 1 or 2 intercalary teeth or denticles that arise between apicodorsal and apicoventral teeth of apical fork, or arise from the dorsal base of apicoventral tooth
...10
10(9) Apical fork of mandible with a single intercalary tooth or denticle that arises between apicodorsal and apicoventral teeth, or arises from the dorsal surface of apicoventral tooth
...11
  Apical fork of mandible with two intercalary teeth or denticles that arise between apicodorsal and apicoventral teeth, often represented by a distinct intercalary tooth accompanied by a less conspicuous denticle
11 (9) Ventral surface of petiole with spongiform tissue present beneath node; cephalic dorsum with a pair of erect hairs near highest point of vertex and another pair near occipital margin; eye with 15 or more ommatidia in total; larger species, HW 0.44 - 0.52 mm (TX)
  Ventral surface of petiole without a trace of spongiform tissue; cephalic dorsum lacking a pair of erect hairs near highest point of vertex, with a pair near occipital margin; eye minute, usually with a total of 4 ommatidia; small species, HW 0.33 - 0.37 mm (keys out twice)
12(3) In full face view and with mandibles fully closed only 3 teeth visible, 2 preapical teeth and one very long apicodorsal tooth which extends over the tooth on the opposite mandible and beyond the outer margin of the opposite mandible; all of the hairs on the leading edge of the scape are curved toward the apex; the outer (dorsal) surface of the hind basitarsus without flagellate projecting hairs; scape short and the head broad (SI < 55, CI 100 or more)
  In full face view and with mandibles fully closed numerous small teeth and denticles present and without the extremely long apicodorsal tooth; some of the hairs on the leading edge of the scape are curved toward the scape base; the outer surface of the hind basitarsus with 1-3 freely projecting fine flagellate hairs; the scape is long and the head is narrow (SI >60, CI 68-79)
...13
13(12) The basal and 2 succeeding mandibular teeth triangular and acute with the second tooth being longer than the basal tooth; the postpetiolar disc without posteriorly curved spatulate hairs; mesonotal dorsum with a pair of erect simple hairs; in full face view the anterior and lateral margins of the clypeus meet in angular corners; scape relatively short (SI 65-69)
  The basal and third tooth triangular and acute, second tooth broad and bluntly rounded, basal tooth longer than the second or third; postpetiolar disc with posteriorly curved spatulate hairs; mesonotal dorsum without erect hairs; the anterior and lateral margins of the clypeus meet in rounded curves; scape longer (SI 79-84)
14(1) Petiole without any spongiform tissue ventrally
...15
  Petiole with a conspicuous spongiform crest or curtain ventrally; the pleurae, side of propodeum, and postpetiolar disc smooth; first tergite of gaster smooth (behind basigastral costulae); first sternite of gaster without sculpture or with sculpture only near apex
...17
15(14) Pleurae, side of propodeum, and postpetiolar disc reticulate-punctate; the first tergite of gaster finely and densely striolate-punctulate everywhere; first sternite of gaster finely shagreened or punctulate (at least basally and laterally)
  Mesopleurae, petiolar and postpetiolar disc mostly lacking sculpture, shiny; first sternite of gaster weakly or not shagreened, appearing shiny
...16
16(15) Erect hairs scarce on body, those present coarse to slightly clavate; sides of pronotum and propodeum reticulate-punctate; head pyriform in frontal view; postpetiole with at least some spongiform tissue present ventrally (only known from queens: LA, MS)
  Entire body and head with numerous, dense, elongate hairs; entire side of mesosoma lacking sculpture, shiny; head triangular in frontal view; postpetiole lacking spongiform tissue ventrally (only known from queens: FL, MS)
17(14) Entire side of mesosoma reticulate-punctate; pronotal dorsum with arched transverse ridge with curved row of spoon-shaped hairsn (queens have reduced sculpture on mesopleurae)
  Sides of mesosoma with at least some areas lacking scupture, shiny; pronotum without curved row of hairs
...18
18(17) In anterior view the clypeus with an apicodorsal series of 4-6 stout standing long hairs that radiate from the apex much like the ribs of a fan; when viewed in profile the clypeal dorsum has a pair of long wire-like hairs that arise about midlength and incline posteriorly from just above their bases and then curve smoothly upwards so that the apical half or more of the shaft is directed vertically or almost so
...19
  The clypeus without a series of stout long hairs radiating from apex like ribs on a fan; clypeal dorsum without long wire-like hairs
...20
19(18)   The fan of long hairs radiating from clypeus strongly bulbous at their apices and in profile these hairs curved posteriorly
  The fan of long hairs radiating from clypeus are simple at their apices and these hairs are not obviously curved posteriorly
20(18) In full face-view and mandibles fully closed the masticatory margin does not have a distinct diastema (a gap or space) present basally (if basal lamella concealed by clypeus, then gap between the basal tooth and the anterior margin of clypeus is shorter than the length of the basal tooth, if basal lamella is exposed at full closure then the diastema between the basal lamella and basal tooth is absent or shorter than the length of basal tooth
....21
  In full face view and mandibles fully closed the masticatory margin has a distinct diastema present basally (if basal lamella concealed by clypeus, then gap between the basal tooth and anterior margin of clypeus is greater than the length of the basal tooth, if the basal lamella is exposed, then the diastema between the basal tooth and basal lamella is longer than the length of the basal tooth
...30
21(20) The basal area on the dorsal surface of fully closed mandible with a distinct sharp transverse edge or rim that runs across the width of the mandible parallel to and in front of the anterior margin of the clypeus; the pronotum is sharply marginate dorsolaterally with the dorsum trasversely flattened and without sculpture; the first tergite of the gaster without standing hairs of any type
  The basal area on the dorsal surface of the mandible without a distinct sharp transverse edge or rim parallel to margin of clypeus; the pronotum not marginate dorsolaterally and transversely convex with sculpture; some type of standing hairs present on the first tergite of gaster
...22
22(21) In full face view the hairs that project from the lateral clypeal margin are fine, conspicuously J-shaped, and curved posteriorly
  In full face view the hairs that project from the lateral clypeal margin are not J-shaped and are curved or inclined anteriorly
...23
23(22) The leading edge of the scape has row of conspicuous projecting curved hairs present of which one or more, distal to the subbasal bend, curve toward the base of the scape
...24
  All projecting hairs on the leading edge of scape curve toward apex of scape
...26
24(23) The basal lamella immediately followed by a row of 7 coarse conical teeth and without a trace of a diastema; the anterior margin of the clypeus shallowly concave; dorsally and near the occipital margin of head a transverse row of 4 long, erect, and very slender hairs present; in full face view a stout, simple, apicoscrobal hair present that curves anteriorly (common)
  Basal lamella followed by a small diastema (smaller than length of basal tooth) followed by 5 small acute teeth; anterior margin of clypeus transverse to shallowly convex; slender hairs absent occipitally; apicoscrobal hairs absent
...25
25(24) A pair of long flagellate hairs present on the mesonotum; pronotal dorsum indistinctly, but shallowly striolate, mesonotum reticulate-punctate, the two contrasting; the pronotum with a median longitudinal carina; (MI 22-25, CI 71-75) (possible, found in FL and Carolinas)
  Pair of long flagellate hairs not present on mesonotum; pronotum and mesonotum evenly reticulate-punctate dorsally and not contrasting; pronotum without median longitudinal carina (MI 16-20, CI 64-69)
26(23) In full face view basal lamella mostly exposed, occupying at least the basal third of the exposed length of margin; second mandibular tooth from the base the longest
  In full face view basal lamella mostly or entirely concealed; third mandibular tooth the longest
...27
27(26) Clypeal dorsum with dense, short, broadly oval-spatulate to scale-like hairs, these hairs reclinate to appressed in profile; in full face view the hairs that project from the lateral clypeal margin either scale-like or appressed to clypeal margin or broadly spatulate and strongly curved anteriorly
...28
  Clypeal dorsum with long narrow hairs that are simple, slightly flattened, or very narrowly linear-spatulate, these hairs not appressed in profile, but either elevated and inclined anteriorly or curved anteriorly in their apical halves; in full face view the hairs that project from the lateral clypeal margin are fine and simple or narrow and linear-spatulate and inclined anteriorly, only very slightly curved, or mostly straight
...29
28(27) In full face view the hairs on the lateral margin of the clypeus project and curve anteriorly, they are not appressed to the surface and are distinctly longer than hairs on the dorsum of clypeus; the upper margin of scrobe with 1-2 long flagellate hairs projecting laterally; seen in profile, the cephalic dorsum with flagellate hairs behind highest point of vertex
  In full face view the hairs on the lateral margin of the clypeus are scale-like and appressed to the surface and are about the same size as the hairs on the dorsum of the clypeus; upper scrobe margin without any flagellate hairs; seen in profile, the cephalic dorsum without any flagellate hairs
29(27) Hairs on clypeus all very fine and filiform, and apically acute; seen in full face view the hairs that project from the lateral clypeal margin are about the same shape and length as the hairs found mid-dorsally; seen in profile the hairs on the clypeus mid-dorsally are elevated and inclined anteriorly
  Hairs on clypeus all narrowly linear-spatulate or flattened and spatulate in apical half and truncate apically; seen in full face view the hairs that project from the lateral clypeal margin are longer and differently shaped than those hairs found mid-dorsally; seen in profile the hairs on the clypeus mid-dorsally are curved or arched anteriorly
30(20)   The principal basal dental row (of mandible) with 5 teeth followed (distally) by 2 smaller teeth and the third tooth from the base is the longest (note:  these teeth are not always easy to see, a high power microscope is essential and it helps if the mandibles are open)
....31
  The principal basal dental row (of mandible) with 4 teeth followed by 2 smaller teeth, the third tooth from the base is not the longest
....34
31(30) The anterior and lateral margins of the clypeus with a continuous broad groove around periphery; seen in profile the edge of the clypeus has a distinct dorsal border with a more strongly prominent ventral border, the two separated by the evenly concave peripheral groove, both borders visible and concentric in full face view as the lower border projects beyond the upper border; hairs on dorsum and margins of clypeus not spatulate or spoon shaped, but simple, flattened, or splayed or weakly forked apically
...32
  The anterior and lateral margins of the clypeus without a continuous groove; seen in profile the edge of the clypeus may be thick or thin, but distinctly single and without upper and lower borders with a concave peripheral groove between them and in full face view the clypeal margin is simple; hairs on dorsum and margins of clypeus mostly to entirely spatulate or spoon shaped
....33
32(31) In profile the clypeus has a very long erect flagellate hair arising dorsally just in front of the antennal socket (this hair much longer than any other on clypeal dorsum), the dorsolateral margin of the head with 2 pairs of flagellate hairs and another flagellate pair close to the occipital border on the cephalic dorsum (rare)
  No long flagellate hairs in front of antennal sockets, on dorsolateral margin of head, or on cephalic dorsum (rare)
33(31) On the leading edge of the scape all hairs curved or inclined toward apex of scape; the upper scrobe margin has 2-3 long flagellate hairs that project laterally; clypeal dorsum with short spatulate hairs
  On the leading edge of the scape at least 2 or more hairs curve toward the base of the scape; the upper scrobe margin has only one long flagellate hairs projecting laterally; the clypeal dorsum with large spoon shaped hairs that are fully translucent (the first tooth of mandible is distinctly longer than the second) (rare)
34(30) The leading edge of the scape with two or more hairs curved or inclined toward the base of the scape
...35
  The leading edge of the scape with all hairs curved or inclined toward the apex of the scape
...44
35(34) All of the hairs on the dorsum and margins of clypeus are very fine, slender and simple, and acute apically (Keys here and later, the hairs curving on scape in one direction or another are apparently variable)
  Some or all of the clypeal hairs are spatulate, clavate, spoon-shaped, or otherwise modified, not simple and slender
....36
36(35) The hairs on the lateral margin of the clypeus (in full face view) curve anteriorly and the hairs on the anterior margin of the clypeus either curved toward midline or anteriorly, no hairs on margin curved away from midline, outwards, or posterolaterally
....37
  At least one pair of hairs on the clypeal margin curved away from midline, inclined or curved outward, or curved posterolaterally; at least one pair near the midline curved away from the midline
...40
37(36) No humeral hair present on the pronotum; in full face view, the upper scrobe margin without an elongate filiform or flagellate hair projecting laterally
  Filiform or flagellate hair present on the humeral region of the pronotum; upper scrobe margin usually with a filiform or flagellate hair projecting laterally (just behind the level of eye or near apex of scrobe)
...38
38(37) In full face view the entire clypeal dorsum with dense conspicuous broadly spatulate hairs, the hairs found mid-dorsally just slightly shorter and narrower than those on the lateral margin of the clypeus; larger species (HW 0.40-0.43)
  In full face view the clypeal dorsum with narrowly spatulate hairs and the hairs found mid-dorsally tiny, much smaller and narrower than the large hairs on the lateral margin of clypeus; smaller species (HW 0.33-0.38)
....39
39(38) The pair of standing long hairs on pronotal dorsum, pair on mesonotum, and hairs on first tergite of gaster filiform and feebly curved, not flagellate, hairs on first gastral tergite with apices weakly split or flattened; in profile, the maximum depth of petiolar ventral spongiform curtain less than maximum depth of peduncle; head slightly broader (CI 69-74)
  The pair of standing long hairs on pronotal dorsum, pair on mesonotum, and hairs on first tergite of gaster distinctly flagellate; in profile, the maximum depth of petiolar ventral spongiform curtain greater than the maximum depth of peduncle; head slightly narrower (CI 63-65)
40(36) No pronotal humeral hairs present; dorsal (outer) surface of the hind tibia and basitarsus without long flagellate hairs; tibia with short suberect hairs
  Humeral hair present on pronotum; the dorsal (outer) surface of the hind tibia, basitarsus, or both with 1-2 long fine flagellate hairs; the tibia without suberect hairs
...41
41(40) In full face view there are laterally or posteriorly curved hairs present on the anterior margin above the mandibles and all hairs on lateral margins curve posteriorly
  In full face view there are only 1-2 pairs of laterally or posteriorly curved hairs on the anterior margin above the mandible and the hairs on the lateral margins do not curve posteriorly
...42
42(41) The hairs projecting from the lateral clypeal margins are thick and simple, sparse, not strongly curved anteriorly and not forming a regular fringe; in full face view the clypeus is slightly longer than broad and if mandibles are at full closure the lateral clypeal margins continue the line of the outer margin of the mandibles (also keys later)
  The hairs projecting from the lateral clypeal margins are broadly spatulate to spoon-shaped, most or all of them curve anteriorly and usually form a regular fringe; in full face view the clypeus is distinctly broader than long and with mandibles closed the lateral margins of the clypeus are not confluent with the other margins of the mandibles, but far outside of the line of the outer mandibular margins
..43
43(42) In full face view no flagellate apicoscrobal hair present; humeral hair on pronotum is simple, stiff and stout; the mesonotum with erect stout simple hairs; the head broader and scapes shorter (CI 68-72, SI 69-75)
  In full face view there is a flagellate apicoscrobal hair present; humeral hair on pronotum is flagellate, elongate and fine; the mesonotum with one pair of erect fine flagellate hairs; head narrower and scapes longer (CI 61-66, SI 78-82)
44(34) Either some, or all of the hairs on the clypeal dorsum are curved or inclined posteriorly or posterolaterally
...45
  All of the hairs on the clypeal dorsum are curved or inclined anteriorly or anterolaterally
..46
45(44) The lateral margin of the clypeus with distinctly spatulate or spoon-shaped curved hairs; in full face view the clypeus is broader than long; the anterior tip of clypeus not curved upward away from dorsal surface of mandible (CI 66-70, SI 70-74)
  The lateral margin of the clypeus with stiff elongate hairs thickened apically, but not spatulate or spoon-shaped; in full face view the clypeus is slightly longer than broad; the anterior tip of clypeus feebly curved upward away from dorsal surface of mandible (CI 60-64, SI 79-83) .(rare, also keyed earlier)
46(44) Hairs on lateral margin of clypeus forming a regular fringe around clypeus and those hairs curved anteriorly, at least weakly, and shorter in length, only slightly longer than hairs on clypeal dorsum
...47
  Hairs on lateral margin of clypeus not forming a fringe, but much more sparse, curved slightly posteriorly, and longer
47(46) The dorsolateral margin of the head has one freely projecting long flagellate hair; hairs on lateral margins of the clypeus curve anteriorly and are strong, linear-spatulate to weakly spoon-shaped and form a fringe; the hairs on the dorsum of the clypeus are spatulate
 

The dorsolateral margin of the head has two freely projecting long flagellate hairs;hairs on lateral margins of the clypeus curve anteriorly, but are very weak and soft, filiform; the hairs on the dorsum of the clypeus are very slender, simple and acute (Keys here and earlier, the hairs curving on scape in one direction or another are apparently variable).