Solenopsis castor

Solenopsis castor nests on the soil and under stones. Specimens were collected from the extraction of tropical forest litter.

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 small (1.30-1.50 mm total length), dark brown (Mexico and Central America) to medium brown (Caribbean) species. The funicular segments are short, the scape is long, nearly reaching the posterior lateral comer of the head. ‘’’Queen’’’ - The queen is dark brown. The lateral clypeal teeth are poorly developed and the clypeal carinae are weakly defined. The head is coarsely punctate. The scape is very long and nearly reaches the posterior border of the head. The pronotum is coarsely punctated. The metapleuron, petiole and postpetiole are horizontally striated.

The workers of S. castor are superficially similar to Solenopsis terricola (Central America and the Caribbean) in color (especially specimens from the Caribbean), but can be easily separated by the longer scape, the smooth and polished mesopleuron and the slender, completely polished petiole. The widely distributed Solenopsis tenuis is also similar, but is usually concolorous light brown. Direct comparison of types, show no differences between the workers of S. castor and Solenopsis nickersoni. Thompson (1982) described S. nickersoni from Florida on the basis of the worker and then later (1989) described the queen with specimens not associated with workers (Thompson, 1980, 1989). Solenopsis nickersoni will continue to be considered a separate species until queens associated with workers can be compared with queens of S. castor. It is likely the two taxa represent the same species-level taxon.

The workers of S. castor are easily confused with those of the widely distributed, common Solenopsis picea. The minor segments are usually shorter than 0.100 mm in total length (usually greater than 0.120 mm in S. picea and the color is usually dark mahogany brown with yellow legs (S. picea is usually medium brown with the legs nearly concolorous with the mesosoma).

The queens of S. castor are relatively small (total length about 3.00 mm) versus the larger queens of S. picea (usually greater than 4.00 mm total length). The queens could be confused with those of the widely distributed S. tenuis. The punctures on the head are usually sparse and small in both species, although the punctures of S. castor are slightly larger. The eyes of S. castor are oblong in shape, with the anterior border convex and curved, the posterior border is nearly straight. The eye of S. tenuis is nearly circular in shape, with the posterior border being as rounded as the anterior border. Note, Although S. castor does not have a well-developed tooth or flange, a small bump is located at the subpeduncular process. This character can be used to separate from similar species.

Distribution
Mexico (Colima) south to Panama (Chiriqui), Caribbean (Antilles st. Vincent, Grenada, Dominica) and Bolivia.

Distribution based on Regional Taxon Lists
Neotropical Region: Bolivia, Costa Rica, Grenada, Lesser Antilles, Mexico, Nicaragua, Panama, Saint Vincent and the Grenadines.

Nomenclature

 *  castor. Solenopsis castor Forel, 1893g: 391 (w.q.) ANTILLES.

Worker
Pacheco and Mackay (2013) - Measurements (n=4). TL 1.32-1.50 (1.41); HL 0.420-0.462 (0.441); HW 0.360-0.390 (0.375); EL 0.042-0.048 (0.045); ED 0.030-0.036 (0.033); SL 0.294-0.300 (0.297); FSL 0.120; CI 84.4-85.7 (85.1); SI 63.6-71.4 (67.5); PL 0.072-0.096 (0.081); PW 0.090-0.132 (0.102); PI 72.7-86.7 (80.3); PPL 0.096-0.108 (0.102); PPW 0.120-0.150 (0.129); PPI 72.0-85.0 (79.5); WL 0.300-0.360 (0.315); PSL 0.030-0.036 (0.032); PSW 0.024-0.030 (0.027).

Small, concolorous brown, with yellowish appendages; head quadrate, longer than wide, posterior border nearly straight; lateral clypeal teeth angulate, extralateral bumps present; clypeal carinae well defined; eyes small, 3-5 ommatidia; scape long, nearly reaching posterior lateral comer of head; minor funicular segments moderately short; pronotum and mesopleuron smooth and shiny; metapleuron horizontally striated; posterior propodeal margin rounded; petiole wider than postpetiole viewed laterally; petiolar node thickened, without tooth or flange ventrally.

Abundantly hairy, most surfaces are covered with long (0.050-0.100 mm), erect hairs. castor

Queen
Pacheco and Mackay (2013) - Measurements (n=6). TL 2.88-3.72 (3.22); HL 0.480-0.540 (0.514); HW 0.396-0.480 (0.432); EL 0.156-0.162 (0.159); ED 0.120-0.126 (0.123); MOL 0.036-0.042 (0.040); MOD 0.042-0.048 (0.046); SL 0.324-0.378 (0.346); FSL 0.168-0.180 (0.175); CI 78.8-89.9 (83.9); SI 60.7-70.0 (67.4); PSL 0.042-0.054 (0.050); PSW 0.042-0.048 (0.044); PL 0.102-0.138 (0.109); PW 0.180-0.198 (0.183); PI 54.5-76.7 (59.6); PPL 0.126-0.150 (0.142); PPW 0.192-0.240 (0.218); PPI 62.5-70.6 (65.3); WL 0.600-0.720 (0.630).

Small, concolorous dark brown, with lighter appendages; head subquadrate, longer than wide, coarsely punctate, posterior border straight; lateral clypeal teeth poorly developed, extralateral teeth absent; clypeal carinae weakly defined; eyes large; scape long, within one funicular segment from reaching posterior border of head; medial ocellus small; pronotum coarsely punctate, smooth and shiny between punctures; mesopleuron smooth and shiny; posterior propodeal margin rounded, propodeal spiracle small; metapleuron horizontally striated; petiole thick, wider than postpetiole viewed laterally; petiolar peduncle lacking tooth or flange ventrally; petiole and postpetiole horizontally striated.

Abundantly hairy; yellow erect and suberect hairs of various lengths covering all body surfaces (longest 0.015 mm in total length), hairs on petiole and postpetiole curve posteriorly.

Type Material
Pacheco and Mackay (2013) - Worker Antilles Is., St. Vincent, (lectotype worker, 4 paralectotype workers, 1 paralectotype queen [here designated].