Pogonomyrmex serpens

Nothing is known regarding the biology of P. serpens but it is likely to be similar to that of P. cunicularius and P. pencosensis. The only literature note is from Santschi’s (1925) description of var. carnivora saying that Bruch told him that workers collected insects to provision the nest. (Johnson 2015)

Identification
Johnson (2015) - Worker Within the P. cunicularius-group, the combination of: (1) in profile, apex of petiolar node weakly rounded to angulate, (2) inferior propodeal spines acuminate, (3) superior propodeal spines long, length greater than distance between their bases, (4) first gastral tergum moderately coriarious, weakly shining, (5) sculpturing on dorsum of promesonotum and posterior surface of petiolar node coarse, rugoreticulate to vermiculate, (6) propodeal dorsum rugoreticulate to transversely rugose, and (7) bicolored—mesosoma and petiolar node darker than rest of body uniquely characterize this species.

Ergatoid Queen This caste is diagnosed by: (1) ergatoid, with small ocelli on head, (2) in profile, petiolar node angulate, (3) inferior propodeal spines about as wide as high, acuminate, (4) first gastral tergum moderately coriarious, dull to weakly shining, (5) sculpturing on dorsum of mesosoma and posterior surface of petiolar node weak to moderately strong, rugae irregular to moderately rugoreticulate, and (7) bicolored—mesosoma dark red-orange; head, legs, petiolar node, postpetiole, gaster lighter red-orange.

Pogonomyrmex serpens is not known to co-occur with any other P. cunicularius-group species but it is likely to co-occur with both P. cunicularius and Pogonomyrmex pencosensis. Pogonomyrmex serpens can be distinguished from P. cunicularius by the combination of: (1) petiolar node angulate in profile, (2) inferior propodeal spines about as wide as high with an acuminate tip, (3) first gastral tergum moderately to strongly coriarious, dull to weakly shining, and (4) superior propodeal spines long, length greater than distance between their bases. In P. cunicularius: (1) the petiolar node is rounded in profile, (2) the inferior propodeal spines are wider than high with a broadly rounded apex, (3) the first gastral tergum is smooth and polished, strongly shining, and (4) superior propodeal spines are short, length less than distance between their bases. Pogonomyrmex serpens can be distinguished from P. pencosensis by the combination of: (1) sculpturing on dorsum of mesosoma and posterior surface of petiolar node coarse, rugoreticulate to vermiculate, and (2) body bicolored with mesosoma and petiolar node medium to dark orangish-brown to reddish-brown, rest of body lighter. In P. pencosensis: (1) sculpturing on the dorsum of the mesosoma and posterior surface of petiolar is weak to moderately strong, rugae are irregular to moderately rugoreticulate, and (2) the body is concolorous tannish-red.

In describing P. cunicularius var. serpens, Santschi did not note specific differences from the other two forms, but said only that the head was a dark reddish-brown and that sculpturing on both the dorsum and sides of the mesosoma consisted of irregular to vermiculate rugae. The bicolored body and the much stronger and more irregular to vermiculate sculpturing on the mesosoma make this form morphologically distinct from both P. cunicularius and P. pencosensis.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Bolivia, Paraguay.

Habitat
Pogonomyrmex serpens is a lowland species that inhabits sites at elevations from 45–905 m. This species is mostly restricted to the Humid Chaco and northern portions of the Dry Chaco ecoregions as defined by Olson et al. (2001), with three additional records outside the northern and western edges of the Dry Chaco. (Johnson 2015)

Castes
Males have yet to be collected.

Nomenclature

 *  serpens. Pogonomyrmex cunicularis var. serpens Santschi, 1922b: 349 (w.) BOLIVIA. Junior synonym of cunicularius: Kusnezov, 1951a: 251. Status as species: Johnson, 2015: 56. Senior synonym of carvinora: Johnson, 2015: 56.
 * carnivora. Pogonomyrmex cunicularis var. carnivora Santschi, 1925e: 155, fig. 2 (w.) ARGENTINA. Junior synonym of cunicularius: Kusnezov, 1951a: 251. Revived from synonymy and raised to species: Wheeler, G.C. & Wheeler, J. 1972b: 236. Junior synonym of cunicularius: Bolton, 1995b: 340; of serpens: Johnson, 2015: 56.

Description
Johnson (2015):

Worker
Lectotype (n = 12). HL 2.40 (2.00–2.33); HW 2.02 (1.65–2.00); MOD 0.37 (0.32–0.42); OMD 0.76 (0.46–0.62); SL 1.74 (1.58–1.81); PNW 1.38 (1.15–1.34); HFL 2.71 (2.22–2.79); ML 2.77 (2.41–2.76); PW 0.49 (0.43–0.52); PPW 0.66 (0.56–0.72). Indices: SI 86.14 (89.07–97.21); CI 84.17 (81.13–87.50); OI 18.32 (17.88–22.42); HFI 134.16 (127.59–143.96).

Head elongate (CI = 81.13–87.50), widest immediately posterior to mandibles, narrowing posterior to eyes; posterior margin flat to weakly convex in full-face view. Cephalic dorsum with moderately coarse, wavy to irregular longitudinal rugae or weakly rugoreticulate; in full-face view, medial rugae diverging weakly toward posterior corners of head. Cephalic interrugae weakly to moderately granulate, weakly shining. Vertex weakly to moderately rugose, dull to weakly shining. Anterior margin of clypeus flat to weakly convex; dorsal surface with several subparallel longitudinal or oblique rugae. Mandibles with six teeth; mandibular dorsum coarsely rugose. Eyes small, MOD ranging from 0.15–0.19x HL. In profile, eyes situated anterior to middle of head, OMD = 1.27–1.75x MOD. Antennal scapes long (SI = 86.14–97.21), surpassing vertex by less than length of first funicular segment; entire scape with longitudinal striae. Basal flange of scape well-developed with carinate margin. Psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral side of head.

Promesonotal profile weakly convex, propodeum flat; all mesosomal surfaces with irregular rugae or rugoreticulate to vermiculate. In dorsal view, humeral shoulders of pronotum rounded. Dorsum of promesonotum and sides of pronotum rugoreticulate to vermiculate, dorsum of pronotum sometimes transversely rugose; mesopleura with irregular rugae that angle posterodorsally. Superior propodeal spines long, narrowing to acuminate tip, length greater than distance between their bases; spines connected by well-defined keel; irregular transverse rugae to rugoreticulate on propodeal dorsum, rugae traverse ventrally or anteroventrally on sides. Inferior propodeal spines well-developed, triangular, wider than high, with angulate to acuminate tip. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma smooth to weakly granulate, weakly shining to shining. Legs long (HFL = 2.22–2.79 mm), weakly to moderately coriarious to granulate, weakly shining.

Peduncle of petiole about 0.8x as long as petiolar node, anteroventral margin with acuminate spine. In profile, posterior surface of petiolar node flattened; node asymmetrical with anterior surface shorter than posterior surface, apex weakly rounded to angulate, usually weakly elevated above posterior surface. In dorsal view, petiolar node about 1.5x longer than wide, widest near anterior margin. Posterior surface of petiolar node with coarse, irregular rugae to rugoreticulate, interrugae weakly to moderately punctate, weakly shining. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing towards anterior margin, maximum width about equal to length, strongly granulate-punctate or with weak irregular, transverse rugae, dull to weakly shining. First gastral tergum moderately coriarious, weakly shining.

Erect to semi-erect yellowish pilosity moderately abundant on head, variable in length. Moderately abundant suberect yellowish pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant subdecumbent to decumbent yellowish setae. Mesosoma, petiolar node, postpetiole, and first gastral tergum with moderately dense, erect setae, mostly similar in length, longest hairs on posterior gastral terga; longest hairs on rest of body rarely > 0.5x MOD. Bicolored with mesosoma and petiolar node darker than rest of body, but color varies geographically. In Argentina, the mesosoma and petiolar node are reddish-orange to reddish-brown, rest of body ferruginous orange. Specimens from Paraguay were darker, with the mesosoma brownish to brownish-orange, rest of body lighter reddish-orange to reddish-brown.

Queen
(n = 5). HL 1.97–2.41; HW 1.63–2.20; MOD 0.35–0.43; OMD 0.42–0.66; SL 1.46–1.84; PNW 1.11–1.37; HFL 2.17–2.68; ML 2.37–2.70; PW 0.43–0.53; PPW 0.58–0.74. Indices: SI 73.64–89.57; CI 82.74–93.62; OI 17.27–21.47; HFI 110.00–133.13.

Ergatoid, very similar to workers except for presence of ocelli on head and slightly larger size (HL = 1.97-2.41, HW = 1.63–2.20 for queens: HL = 2.00–2.40, HW = 1.65–2.02 for workers). In full-face view, head elongate (CI = 82.74–93.62), sides of head from mandible to lower eye margin parallel or diverging weakly toward mandibular insertion; posterior margin flat to weakly convex. Cephalic dorsum with longitudinal, wavy to moderately irregular rugae, sometimes becoming rugoreticulate near posterior margin, interrugae weakly to strongly granulate-punctate, dull to weakly shining; vertex rugose, weakly shining to shining. Mandible with six teeth, dorsal surface coarsely rugose. Psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral side of head.

Mesosomal segments fused, mesoepinotal suture often weakly impressed, lacking all morphological structures related to wings. Promesonotum mostly rugoreticulate to vermiculate; propodeum with irregular transverse rugae that traverse ventrally on sides. Superior propodeal spines long; spine length similar to or slightly longer than distance between their bases; inferior propodeal spines well-developed, triangular, wider than high, with angulate to acuminate tip. Peduncle of petiole about as long as petiolar node, anteroventral margin with acute spine-like process. In profile, petiolar node asymmetrical with anterior surface notably shorter than posterior surface, apex angulate. Posterior surface of petiolar node with irregular transverse rugae to rugoreticulate-vermiculate; interrugae weakly punctate, weakly shining to smooth and shining. Postpetiole convex in profile; in dorsal view, maximum width about equal to length; dorsum moderately to strongly granulate-punctate, with weak irregular transverse rugae, or rugoreticulate, dull to weakly shining. First gastral tergum moderately to strongly coriarious, dull to weakly shining. Most body surfaces with moderately abundant suberect to erect, short, yellowish setae. Bicolored—mesosoma dark red-orange; head, legs, petiolar node, postpetiole, gaster lighter red-orange.

Type Material
P. serpens: Syntypes, 2 workers, BOLIVIA, San José, at two hours on the path to Carumba, #1073 (Lizer and Delétang leg.). MACN worker [CASENT0235269] designated LECTOTYPE by Johnson, 2015: 56. In regard to the type locality, Santschi gave a vague description, saying it was San José, two hours from Carumba, which is likely Corumba, Mato Grosso, Brazil. San José de Chiquitos is the only San José in this part of Bolivia, and it is about 350 km WNW of Corumba. Consequently, I assume that San José de Chiquitos is the type locality.

P. carnivora: Syntypes, 6 workers [MACN], 1 worker MZUSP, ARGENTINA, Santa Fe: Fives Lille, #1614 (Weiser leg.). MACN worker [CASENT0249054] designated LECTOTYPE by Johnson, 2015: 56.

Etymology
The specific epithet, serpens (from Latin, serpens = serpent), apparently refers to a snake. Santschi did not discuss the naming of this species, so its derivation is unclear. The name might refer to the narrow, elongate body of this species.