Solenopsis minutissima

Solenopsis minutissima was collected nesting under a rock in Argentina (Wheeler, 1914).

Identification
A New World thief ant that is a member of the pygmaea species complex.

Pacheco and Mackay (2013) – Worker - The worker is very small and concolorous yellow. The head is elongate and coarsely punctate. The scape is short at 0.185 mm. The minor funicular segments 3-8 are short as well at 0.078 mm in total length. The eye is extremely small with 1-2 ommatidia and has a maximum diameter of 0.012 mm. Queen - Not seen. Emery 1906, "The female is easy to recognize for its minute stature, elongate head and short, thick legs and antennae." Male - The male is brown with yellowish appendages. The head is as wide as long and coarsely punctate. The propodeal spiracle is large at 0.250 mm in width. The propodeum, petiole and postpetiole are completely horizontally striated.

This species is a small, pale yellow, slender ant, with few erect hairs on the mesosoma. It is also one of the species with long apical antennal segments (segments 9-10), longer than the combined length of the minor segments of the funiculus (others include Solenopsis leptanilloides and Solenopsis dysderces). Solenopsis minutissima is similar to Solenopsis leptanilloides and Solenopsis dysderces but can be separated as it has a quadrate shaped head compared to the other two species which have noticeably elongate heads. Solenopsis minutissima can be easily confused with Solenopsis subterranea as well, as both species have short hairs about the same length on the pronotum and on dorsum of the gaster. It can be separated as the eyes are poorly developed and nearly absent (present and well-defined in Solenopsis subterranea). Additionally, the head of S. minutissima is thicker when viewed from the dorsal to ventral surface. Based on available material, S. minutissima is found in Argentina and the southernmost distribution of S. subterranea is Venezuela.

Keys

 * Key to New World Solenopsis Species Complexes
 * Key to Solenopsis pygmaea species complex / Clave a las obreras del complejo Solenopsis pygmaea

Distribution
Pacheco and Mackay (2013) - Argentina, Buenos Aires, Catamarca (Tucuman); Guianas; Trinidad; Mexico, Hildalgo (Kempf 1972 [possibly S. subterranea mididentified). Note, the Mexican records, from Wheeler (1914) are probably misidentifications of Solenopsis pollux or Solenopsis subterranea.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil, French Guiana, Guyana, Mexico, Suriname, Trinidad and Tobago.

Nomenclature

 *  minutissima. Solenopsis minutissima Emery, 1906c: 133, fig. 15 (w.m.) ARGENTINA. Wheeler, W.M. 1914b: 44 (q.). Senior synonym of brevipes: Pacheco & Mackay, 2013: 229.
 * brevipes. Solenopsis brevipes Emery, 1906c: 135, fig. 16 (w.) ARGENTINA. Junior synonym of minutissima: Pacheco & Mackay, 2013: 229.

Worker
Pacheco and Mackay (2013) - Measurements (n=5). TL 1.20-1.32 (1.29); HL 0.330-0.360 (0.347); HW 0.252-0.258 (0.257); EL 0.006-0.018 (0.013); ED 0.006-0.018 (0.012); SL 0.180-0.192 (0.185); FSL 0.072-0.084 (0.078); CI 71.7-78.2 (74.1); SI 51.7-54.5 (53.3); PL 0.072-0.084 (0.074); PW 0.078-0.096 (0.089); PI 75.0-92.3 (84.1); PPL 0.084-0.102 (0.091); PPW 0.096-0.114 (0.102); PPI 84.2-100 (89.5); WL 0.240; PSL 0.018; PSW 0.018.

Small; concolorous yellow; head quadrate, elongate, coarsely and densely punctate; lateral clypeal teeth well developed, extralateral teeth absent; clypeal carinae weakly defined; scape short, barely exceeds half-length of head; minor funicular segments 3-8 short; eyes small, with little pigmentation (eyes usually not defined), 1-2 ommatidia; mesosoma mostly smooth and shiny; posterior propodeal margin rounded; propodeal spiracle round, small; metapleuron horizontally striated; petiole wider than postpetiole viewed laterally; petiolar node rounded, triangular, peduncle without tooth or flange ventrally; postpetiolar node oval viewed dorsally, lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; erect and suberect hairs covering all body surfaces; hairs appear uniform in total length (majority 0.036-0.048 mm).

Male
Pacheco and Mackay (2013) - Measurements (n=4). TL 3.12-3.24 (3.16); HL 0.480; HW 0.480-0.516 (0.495); EL 0.180; ED 0.162; MOL 0.054-0.066 (0.059); MOD 0.048-0.066 (0.056); SL 0.252-0.264 (0.258); FSL 1.32; CI 100-108 (103); SI 52.5-55.0 (53.8); PSL 0.066-0.084 (0.072); PSW 0.060; PL 0.150-0.162 (0.155); PW 0.222-0.240 (0.233); PI 62.5-70.3 (66.5); PPL 0.210-0.222 (0.213); PPW 0.240-0.270 (0.248); PPI 77.8-92.5 (86.3); WL 0.720-0.780 (0.735).

Moderately large; concolorous brown, with yellowish appendages; head as wide as long, coarsely punctate; anterior clypeal margin convex, lacking carinae; scapes and funicular segments long; eyes large, extend 0.108 mm past lateral margin of head; medial ocellus small; pronotum coarsely punctate; posterior propodeal margin rounded; propodeal spiracle large; propodeum horizontally striate; petiole wider than postpetiole viewed laterally; petiolar and postpetiole horizontally striate, both lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; erect and suberect hairs covering all body surfaces; hairs on head 0.150 mm in total length; hairs on pronotum 0.120-0.150 mm in length; hairs on petiole, postpetiole and gaster curve posteriorly.

Type Material
Argentina, Buenos Aires, Nunez 13.18. Silvestri. M.C.Z. cotype 22755 (lectotype worker [here designated], 1 paralectotype worker and 1 paralectotype male ). Argentina, Buenos Aires, Nunez 17.11.99, Museo Genova, Coll. C. Emery (dono 1925) (Syntypus 8 workers, 3 males, . Solenopsis brevipes Emery, Argentina. Entre Rios, Chajari.