Trachymyrmex, Forel, 1893

Rabeling, Ch., Cover, S. P., Johnson, R. A. & Mueller, U. G., 2007, A review of the North American species of the fungus-gardening ant genus Trachymyrmex (Hymenoptera: Formicidae)., Zootaxa 1664, pp. 1-53 : 4-6

Key to workers & queens of Trachymyrmex species occuring in the United States

Trachymyrmex workers within a colony often vary slightly in size, thus some of the characters used in this key can vary within colonies. For best results, we recommend checking the characters on several specimens from each collection or nest series when using this key. To increase the usability, we highlight the morphological characters used in this key by pointing arrows to the respective characters in one representative figure per couplet; the highlighted character can be seen in figures marked with bold font, underlining, in square brackets (e.g.: in couplet (1) see figure [8B] for shallow antennal scrobe described by preocular and frontal carinae). The key works for queens also if one substitutes the word "pronotal" for "promesonotal" when referring to mesosomal teeth or spines (except references to "median anterior pronotal tubercles," which are not present in queens).

1 In full-face view, preocular and frontal carinae subparallel, converging gradually towards the posterior corners of the head, forming a long, shallow antennal scrobe (Figures 8 [8B]& 19).................................2

- In full-face view, preocular and frontal carinae NOT subparallel, frontal carinae often extending towards the posterior corners of the head, but preocular carinae always curving mesially towards the frontal carinae, rarely actually touching them (Figures 1, 3, 5 [5B], 6, 10, 11, 12, 13, 15, 17) .................................... 3

2 In full-face view, antennal scapes reaching or just slightly surpassing the posterior corners of head. In side view, center of clypeus with several long, conspicuous, coarse, erect hairs, nearly as long as those in the row of long hairs along the anterior clypeal margin that project over the dorsal surface of the mandibles (Figure 19) ........................................................................................................................................ turrifex

- In full-face view, antennal scape surpassing posterior corner of head by the maximum diameter of the scape or more. In side view, clypeus usually with only a few short, stiff erect hairs present, when present these are much shorter than the row of long hairs along the anterior clypeal margin (Figure 8) ................... ................................................................................................................................................... jamaicensis

3 Frontal carinae relatively short, not extending towards the posterior corner of the head. Preocular carinae curving strongly to meet the frontal carinae, forming short, distinctive "scrobes", that end slightly behind the level of the eye (Figure [10B]). Antennal scape long (SI 117-152), narrowing abruptly as it approaches the antennal insertion, a small but conspicuous lobe is present just distal to the narrowing (Figure [10C]) (Figures 10 & 11) ................................................................................................ nogalensis

- Frontal carinae long, extending well past the eye towards the posterior corners of the head. In side view, preocular carinae not joining the frontal carinae (rarely touching the carinae in T. carinatus ). Antennal scapes shorter (SI 113). Scape gradually narrowing as it approaches the antennal insertion, lobe as described above absent (Figures 1, 3, 5, 6, 12, 13, 15 & 17) ...................................................................... 4

4 In full-face view, frontal lobes prominent, shaped uniquely as in Figure [1B], the posterior margin of the lobe forming a broad notch with the posterior portion of the frontal carinae. Antennal scapes long (worker SI 103-113; queen SI 96-105). First gastric tergite strongly tuberculate (Figure 1) ................. arizonensis

- In full-face view, frontal lobes simple, rounded or triangular (Figure [3B]). Antennal scapes shorter (worker SI 105; queen SI 96). Gastric tubercles variously developed, sometimes small or nearly absent (Figures 3, 5, 6, 12, 13, 15 & 17) ................................................................................................................. 5

5 Combining the following: in larger workers head clearly broader than long, slightly broader than long to square in smaller workers (CI 100-111); posterior border notably emarginate, in full-face view head appearing cordate in larger workers (Figure [17B]). Propodeal spines longer than the distance separating their bases. Color black to blackish red (Figure 17) ........................................................................... smithi

- Head shape variable, usually more or less square, sometimes broader than long. Posterior border weakly to moderately emarginate, but head never appearing cordate in full-face view -even in larger workers (Figure [3B]). Propodeal spines or teeth variable in length, often as long as or shorter than the distance separating their bases. Color never black or blackish (Figures 3, 5, 6, 12, 13 & 15) .................................. 6

6 Combining the following: median anterior pronotal tubercles well-developed, in anterior view nearly always upright and toothlike, the apices often with 2-3 small "peaks." Preocular carina never closely approaching the frontal carina in full-face view. First gastric tergite tuberculate (Figure 15) ....................... .............................................................................................................................................. septentrionalis

- Median anterior tubercles poorly developed or absent altogether, not upright or toothlike in anterior view, when present taking the form of small denticles or low, broadly pyramidal mounds. Preocular carinae variable, sometimes closely approaching the frontal carinae in full face view. Tuberculi on first gastric tergite sometimes absent or minute (Figures 3, 5, 6, 12 & 13) .................................................................... 7

7 Preocular carinae traversing nearly the entire antennal scrobe as it curves towards the frontal carina, closely approaching or sometimes even appearing to touch the frontal carinae in full-face view. Frontal lobes usually more or less symmetric (evenly rounded). First gastric tergite conspicuously tuberculate (Figure 3) ....................................................................................................................................... carinatus

- Preocular carinae shorter, in full-face view never closely approaching or appearing to touch the frontal carinae in full-face view. Frontal lobes variable, sometimes asymmetric with the anterior margin longer than the posterior margin. Tubercules miniscule or absent on first gastric tergite (Figures 5, 6, 12 & 13)...8

8 In full-face view, frontal lobes rounded (rarely subtriangular), more or less symmetrical, anterior and posterior sides equal in length or anterior side slightly longer than posterior (Figures 5 & 6)........ desertorum

- In full-face view, frontal lobes subtriangular (rarely rounded), strongly asymmetric, the anterior side of the lobe often 2x as long as the posterior side or more (Figures 12 & 13).................................... pomonae

Key to the males of Trachymyrmex species occuring in the United States

Trachymyrmex nogalensis is not included in this key because the male of this species is unknown.

1 Ventrolateral pronotal tooth absent and dorsolateral pronotal tooth well-developed (Figures 9 & 20)......2

- Ventrolateral pronotal tooth often clearly present, if indistinct or absent then the dorsolateral pronotal tooth is also indistinct or absent (Figures 2, 4, 7, 14, 16 & 18)...................................................................3

2 In dorsal view, dorsolateral pronotal tooth short, sharp, and triangular. Setae on first gastric tergite sparse, decumbent or appressed (Figure 20)................................................................................................. turrifex

- In dorsal view, dorsolateral pronotal tooth a needlelike spine. Setae on first gastric tergite short, moderately abundant, more or less recurved, and mostly erect (Figure 9).......................................... jamaicensis

3 In dorsal view, dorsolateral pronotal tooth distinct, sometimes even forming a short spine (Figures 2, 7 & 16)................................................................................................................................................................4

- In dorsal view, dorsolateral pronotal tooth very small or entirely absent, sometimes reduced to an angulate ridge, but not present as a tooth or spine (Figures 4, 14 & 18)...................................................................6

4 In lateral view, irregular rugulae present on all surfaces of pronotum; interrugal spaces granulate. Antennal scrobe granulate, with at least several transverse rugulae distributed over the anterior 3/4 (Figure 7)...... .................................................................................................................................................... desertorum

- Pronotum generally lacking irregular rugulae, sometimes a few inconspicuous rugulae present near dorsolateral pronotal teeth. Antennal scrobe granulate, with 1-4 transverse rugulae near anterior margin or rugulae absent altogether..................................................................................................................................5

5 Surface of first gastric tergite bumpy due to the presence of numerous small tubercles; each tubercle bears a decumbent, recurved setae. Dorsoventral pronotal teeth large, narrowly triangular in dorsal view (Figure 2)................................................................................................................................................. arizonensis

- Surface of first gastric tergite finely granulate, lacking small tubercles, short, suberect somewhat recurved setae moderately abundant. Dorsoventral pronotal teeth short, broadly triangular in dorsal view (Figure 16)......................................................................................................................................... septentrionalis

6 Small species (HL 0.6-0.75; HW 0.6-0.75). In full-face view, preocular carinae weakening rapidly as it passes the posterior border of the eye and turns towards the midline, past the eye the carina not more prominent than adjacent rugulose sculpture on the posterior half of the head, rear border of scrobe sometimes indistinct (Figure 14)............................................................................................................ pomonae

- Larger species (HL 0.72-0.84; HW 0.75-0.87). In full face view, preocular carina remaining a distinctive vertical ridge as it passes the eye and turns towards the midline, past the eye the carina clearly more prominent than adjacent rugulose sculpture on the posterior half of the head, and remaining fully developed until reaching the midpoint of the posterior border of the scrobe (Figures 4 & 18)....................................6

7 In dorsal view, mesoscutum slightly broader than long, sculpture coarsely and irregularly rugulose and granulate, sometimes a faint longitudinal pattern is discernable (Figure 4).................................. carinatus

- In dorsal view, mesoscutum about as long as broad, sculpture predominantly longitudinally rugulose, interrugal spaces finely granulose (Figure 18)................................................................................... smithi