Key to Solenopsis fugax species complex

AntWiki: The Ants --- Online

The following is based on: Pacheco, J.A. & Mackay, W.P. 2013. The systematics and biology of the New World thief ants of the genus Solenopsis (Hymenoptera: Formicidae). Edwin Mellen Press, Lewiston, New York. 501 pp. PDF

The fugax species complex is a group of New World thief ants in the genus Solenopsis.

There are two keys to workers. The northern species, which follows just below, and a South American key that is found further down the page.

Key to the workers of North American (north of Colombia) species of the fugax Complex


  • Western Mexico to Colombia; dimorphic; minor workers total length 1.1-1.4 mm, major workers 1.7-2.5 mm; concolorous yellow to brown; eye with 3-8 ommatidia; extralateral teeth nearly absent (Fig. 132) to fully developed (Fig. 134) and equal in size to lateral teeth; petiole and postpetiole smooth and shiny (Fig. 133) or horizontally rugose viewed laterally. . . . . 2
  • Continental USA, North Carolina to Arizona; monomorphic; total length 1.4-2.5 mm; concolorous yellow; eye with 2-6 ommatidia; extralateral teeth always present, either angulate or well developed; petiole and postpetiole always smooth and shiny. . . . . 3


return to couplet #1

  • Central and southern Mexico to Colombia; concolorous medium to dark brown; minor worker, small, total length 1.1-1.4 mm; head length 0.35-0.38 mm; scape length shorter, 0.22-0.24 mm; eye larger, with 3-5 ommatidia (difficult to distinguish); petiolar peduncle with tooth ventrally; major worker, small, total length 1.5-1.7 mm; head length 0.50-0.53 mm, dorsum of head with sculpturing, entirely rugose and coarsely punctate; scape shorter, 0.26-0.28 mm; extralateral teeth reduced, nearly absent; eye larger, with 5-8 ommatidia; petiole and postpetiole with sculpturing, horizontally rugose to punctate . . . . . Solenopsis vinsoni
  • Central Mexico, Baja California; concolorous yellow; minor worker, larger, total length 1.3-1.5 mm; head length 0.42-0.48; scape length longer, ~0.3 mm; eye smaller (Fig. 132), with ~3 ommatidia; major worker, larger, total length 1.8-2.5 mm; head length 0.54-0.62 mm; dorsum of head without sculpturing, smooth and shiny between punctures; scape longer, 0.36-0.42 mm; extralateral teeth larger, well developed; eye smaller, with 3-5 ommatidia; petiole and postpetiole without sculpturing, smooth and shiny . . . . . Solenopsis johnsoni


return to couplet #1

  • Southwestern USA, Arizona to Texas; larger, total length 2.2-2.5 mm, head length 0.60-0.64 mm; extralateral teeth sharp , well developed, nearly equal in size to lateral teeth; frontal lobes lacking vertical striae ; meosopleuron lacking sculpturing (Fig. 139) or horizontally striated; eye larger, with 3-6 ommatidia . . . . . 4
  • Widely distributed, North Carolina to New Mexico; smaller, total length 1.4-1.9 mm, head length 0.43-0.51 mm; extralateral teeth angulate, smaller than lateral teeth; mesopleuron always lacking sculpturing; eye smaller, with 2-5 ommatidia . . . . . 5


return to couplet #3

  • Frontal carinae diverging anteriorly; mesopleuron lacking sculpturing; eye relatively large, eye length 0.06-0.07 mm, 5-6 ommatidia; scape longer, 0.40-0.47 mm; narrowest distance between clypeal carinae wide at 0.1 mm; common New Mexico to western Texas . . . . . Solenopsis krockowi
Solenopsis krockowi casent0104467 head 1.jpg
Solenopsis krockowi casent0104467 profile 1.jpg
  • Carinae nearly parallel; mesopleuron horizontally striated; eye smaller, eye length ~0.04 mm, 3-5 ommatidia; scape shorter, 0.33-0.35 mm; distance between clypeal carinae narrow at less than 0.1 mm; rarely collected central to eastern Texas . . . . . Solenopsis pilosula
Solenopsis pilosula casent0172923 head 1.jpg
Solenopsis pilosula casent0172923 profile 1.jpg


return to couplet #3

  • Head wider, 0.43-0.51 mm; eye with 2 ommatidia; postpetiole circular (seen from above); common, eastern Texas to Florida . . . . . Solenopsis pergandei
Solenopsis pergandei casent0104506 head 1.jpg
Solenopsis pergandei casent0104506 profile 1.jpg
  • Head narrower, 0.35-0.43 mm; eye larger; postpetiolar node wider than long (seen from above); rare, southern New Mexico . . . . . Solenopsis melina

Key to the workers of the South American species of the fugax complex

It is possible that some species listed as monomorphic are actually dimorphic and the majors have not yet been collected.


  • Dorsum of head mostly covered with rugulae, which meld into shiny subsurface; petiole somewhat thickened, in form of dome viewed laterally; Colombia . . . . . 2S
  • Dorsum of head mostly smooth and glossy between punctures, if rugulae present, mesosoma mostly sculptured and dull; petiole usually narrow as seen in profile, not dome-shaped; widely distributed in South America . . . . . 3S


return to couplet #1S

  • Mesosoma and sides of petiole and postpetiole mostly smooth and glossy . . . . . Solenopsis rugiceps
Solenopsis rugiceps casent0902340 p 1 high.jpg
  • Mesosoma and sides of petiole and postpetiole mostly sculptured, with punctures and striae . . . . . Solenopsis vinsoni


return to couplet #1S

  • Weakly dimorphic; concolorous yellow; eye relatively large with 8-10 relatively distinct ommatidia; flange-like angle present ventrally on petiolar peduncle; anterior clypeal margin with 2 well developed lateral teeth (extralateral teeth reduced to bumps, nearly absent); northeastern Brazil to northeastern Argentina . . . . . Solenopsis orestes
  • Monomorphic and dimorphic; concolorous yellow to dark brown; eye generally small, ranging from 1-10 mostly fused ommatidia; tooth usually present ventrally on petiolar peduncle; anterior clypeal margin with 4 well developed teeth (occasionally extralateral teeth angulate but always present at least on major) . . . . . 4S


return to couplet #3S

  • Clypeus of minor worker with 4 clypeal teeth (2 lateral, 2 extralateral), all 4 teeth about equal in shape and size, clypeus of major with 4 well developed clypeal teeth; eye larger, 3-10 ommatidia . . . . . 5S
  • Clypeus of minor with 2 well developed lateral teeth, extralateral teeth smaller than lateral teeth, angulate; clypeus of major with 4 well developed clypeal teeth, lateral and extralateral teeth closely spaced (0.03 mm between tips); eye smaller, at least 1 ommatidium; La Plata, Argentina . . . . . Solenopsis tetracantha
Solenopsis tetracantha casent0178148 head 1.jpg
Solenopsis tetracantha casent0178148 profile 1.jpg


return to couplet #4S

  • Dimorphic, larger in total length, minor worker 1.8-2.6 mm, major worker 2.9-3.2 mm; eye large 5-10 ommatidia; scape length longer, 0.36-0.55 mm S. . . . . 6S
  • Monomorphic, smaller in total length, workers 1.4-1.7 mm; eye smaller 3-5 ommatidia; scape length shorter, 0.26-0.30 mm . . . . . 7S


return to couplet #5S

  • Dimorphic, minor worker, total length ~2.16 mm; frontal lobes vertically striated; pronotum finely punctate; eye large, width 0.03-0.04 mm, with 7 ommatidia; concolorous yellow; minor funicular segments longer 0.18-0.21 mm; major worker, larger, 2.9-3.2 mm, head length 0.75-0.78 mm; frontal lobes vertically striated; pronotum finely punctate; eye larger, width 0.50-0.55 mm, 8-10 ommatidia; concolorous golden brown; scape length longer, 0.54-0.55 mm; minor funicular segments longer, 0.24-0.28 mm; southern Chile . . . . . Solenopsis thoracica
  • Apparently monomorphic, workers 1.8-2.7 mm, head length 0.52-0.71; frontal lobes with sculpturing; pronotum coarsely punctate; eye smaller, 5-8 ommatidia; concolorous golden brown; minor funicular segments shorter, 0.14-0.18 mm; southern Chile and Argentina . . . . . Solenopsis germaini
Solenopsis germaini casent0904632 h 1 high.jpg
Solenopsis germaini casent0904632 p 1 high.jpg


return to couplet #5S

  • Postpetiole with ventral tooth; concolorous yellow to light brown; pronotum coarsely punctate; posterior propodeal margin angulate; southern Brazil and southeastern Argentina . . . . . Solenopsis patagonica
Solenopsis patagonica casent0103221 head 1.jpg
Solenopsis patagonica casent0103221 profile 1.jpg
  • Postpetiole lacking tooth or bump ventrally; concolorous medium brown; pronotum finely punctate; posterior propodeal margin rounded; southern Brazil, Paraguay and northern Argentina . . . . . Solenopsis westwoodi