Solenopsis tenuis

Solenopsis tenuis nests underground and under logs. Brood and sexuals are found in nests in June in rocky shale soils (Mexico). They were collected in subterranean traps and traps in vegetation baited with Vienna sausage in Mexico and Venezuela. They were also collected with cards baited with tuna. They have been collected in pitfall traps and litter extractions which indicates that they forage above ground. Habitats range from riparian oak/cottonwood forest, transitional dry tropical forest/wet montane forest, wet montane cloud forest, oak ridge forest, pine with hardwoods, montane hardwood forests, to virgin tropical rain forest.

Identification
A New World thief ant that is a member of the molesta species complex. (Key to New World Solenopsis Species Complexes)

Pacheco and Mackay (2013) – Worker - This is a minute, thinly bodied, concolorous pale to medium brown species. The head is quadrate and the eyes are relatively large with 5-7 ommatidia. The minor funicular segments are short, ranging from 0.08 to 0.10 mm in total length. The lateral clypeal teeth are poorly developed with the anterior clypeal border straight between the carinae. The propodeum is finely striated basally. Queen - The queen is medium brown in color. The lateral clypeal teeth are poorly defined and the extralateral teeth are absent. The head is longer than wide and finely punctate. What is striking about this queen is that the propodeal spiracle is large with a width of 0.100 mm. Male - The male is a small black specimen. The median ocellus is large (0.060 mm maximum diameter), the lateral ocelli are about 1/2 the diameter of the median ocellus. They are separated by a distance of 0.070 mm. The mandible is small, with two well-developed teeth (apicalmost) and two poorly developed teeth (basalmost). The anterior face of the petiole is nearly straight, meeting the posterior face at a relatively sharp angle. The apex of the petiole is concave when viewed from the front.

The workers of S. tenuis are similar to those of Solenopsis picta (SE USA), but can be separated by the longer scapes. Workers could be confused with Solenopsis corticalis (Mexico south to Brazil), but are often darker in coloration and the lateral clypeal teeth are more sharply developed. Workers may be confused with Solenopsis picea (Mexico south to Brazil), but the minor segments of the funiculus are shorter (usually> 0.12 mm in S. picea). Solenopsis tenuis is similar to the Galapagos species, Solenopsis gnoma, but can be distinguished as S. gnoma is markedly smaller in total length in both the worker and queen castes. Additionally, S. gnoma has coarser cephalic punctures and more developed lateral clypeal teeth.

Series consisting of only workers cannot always be correctly identified. If queens are available, they are distinguished being dark brown, with the eye relatively large, occupying about 1/2 of the length of the side of the head and the head nearly completely smooth and shiny, with a few, scattered, insignificant punctures. It is difficult to separate queens from those of Solenopsis castor (Mexico south to Bolivia), but where the distributions commonly overlap (Central America), it is usually concolorous medium brown including the appendages, whereas the queen of S. castor is dark brown to black, with brownish-yellow appendages.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Belize, Brazil, Colombia, Costa Rica, Guatemala, Mexico, Panama, Trinidad and Tobago, Venezuela.

Nomenclature

 *  tenuis. Solenopsis tenuis Mayr, 1878: 874 (w.q.) BRAZIL. Forel, 1913l: 222 (m.); Wheeler, G.C. & Wheeler, J. 1955c: 135 (l.). Senior synonym of minuiscens: Pacheco & Mackay, 2013: 322.
 * minuiscens. Solenopsis tenuis var. minuiscens Forel, 1912g: 8 (w.) BRAZIL. Junior synonym of tenuis: Pacheco & Mackay, 2013: 322.

Worker
Pacheco and Mackay (2013) - Measurements (n=6). TL 1.14-1.32 (1.22); HL 0.360-0.408 (0.373); HW 0.294-0.342 (0.308); EL 0.036-0.048 (0.038); ED 0.030-0.036 (0.031); SL 0.240-0.276 (0.256); FSL 0.078-0.108 (0.086); CI 80.0-83.8 (82.6); SI 66.2-76.7 (68.7); PL 0.060; PW 0.084-0.096 (0.088); PI 62.5-71.4 (68.4); PPL 0.084-0.102 (0.093); PPW 0.102-0.120 (0.112); PPI 75.0-94.4 (83.2); WL 0.240-0.300 (0.271); PSL 0.030-0.036 (0.031); PSW 0.024-0.030 (0.029).

Small; concolorous pale brown to dark brown; head slightly longer than wide, finely punctate; lateral clypeal teeth poorly developed, extralateral teeth absent; clypeal carinae weakly defined; scapes long, nearly reach posterior border of head; minor funicular segments 3-8 short; eyes moderately large, 5-7 ommatidia; pronotum smooth and shiny; mesopleuron smooth and shiny; posterior propodeal margin rounded; propodeal spiracle moderately large, round; metapleuron horizontally striated; petiole wider than postpetiole viewed laterally; both petiole and postpetiole smooth and shiny, lacking tooth or flange ventrally.

Moderately hairy, pilosity yellow and light brown; erect and suberect hairs scattered throughout body surfaces; scape with numerous appressed and suberect hairs; hairs on petiole long 0.063-0.120 mm in total length, hairs on petiole and postpetiole curve posteriorly.

Queen
Pacheco and Mackay (2013) - Measurements (n=2). HL 0.636-0.642 (0.639); HW 0.600; EL 0.192-0.204 (0.198); ED 0.204-0.210 (0.207); MOL 0.042-0.048 (0.045); MOD 0.048-0.054 (0.051); SL 0.450; CI 93.5-94.3 (93.9); SI 70.1; PSL 0.096-0.102 (0.099); PSW 0.096-0.102 (0.099); PL 0.144; PW 0.228-0.240 (0.234); PI 60.0-63.2 (61.6); WL 0.900-0.960 (0.930).

(Queen description based on broken types). Moderately large; concolorous medium brown; head longer than wide, wider posteriorly than anteriorly, giving triangular appearance, finely punctate; lateral clypeal teeth poorly developed, extralateral teeth absent; clypeal carinae poorly defined; frontal lobes vertically striated; scape long, nearly reaching posterior border of head; eyes large, extend 0.102 mm past lateral edge of head; medial ocellus small, without pigment; mesosoma smooth and shiny; posterior propodeal margin rounded viewed laterally; propodeal spiracle relatively large, circular; metapleuron horizontally striated; petiolar peduncle lacking tooth or flange ventrally; petiolar spiracle relatively large, maximum diameter 0.030 mm.

Abundantly hairy, pilosity light brown and yellow; erect and suberect hairs of various lengths covering all body surfaces; suberect hairs on dorsum of head 0.120 mm; hairs on dorsum of mesosoma ranging from 0.060-0.150 mm; hairs on petiole up to 0.180 mm, curve posteriorly.

Male
Pacheco and Mackay (2013) - Small; concolorous black; head wider than long, smooth and shiny; anterior clypeal margin convex, lacking teeth or carinae; eye relatively small; lateral ocelli about 1/2 diameter of median ocellus, relatively large, separated by 0.07 mm; mesosoma smooth and shiny; anterior face of petiole nearly straight; apex of petiole concave when viewed anteriorly.

Abundantly hairy, pilosity light brown and yellow; erect and suberect hairs covering all body surfaces; hairs on petiole and postpetiole curve posteriorly.

Type Material
Worker Brazil, Amazonia (lectotype worker, 6 paralectotype workers and 2 paralectotype queens [here designated], and 3 paralectotype males [here designated] , Rosario Santa Fe (Bruch) # 23b. Solenopsis tenuis minuiscens, Brazil, Lomtos (Ris) (Typus, worker Coll. Forel [seen] MHNG).