Solenopsis molesta

This is a common, widely distributed species. Nests are found in the soil (often under stones) and often adjacent to the nests of other species, where it steals food or brood from its host. Specimens have been collected from subterranean, surface and vegetation Vienna sausage bait traps, as well as surface, subterranean and vegetation fire ant bait traps. It is commonly collected in pitfall traps. Reproductives and brood are present throughout the summer. This is also a household pest, although it may not be noticed due to its small size. It hollows out seeds, thus destroying seed in beds. Colonies contain up to a few thousand workers. Sexuals are found in nests from July to October. Nuptial flights occur from late July to early fall, individuals mate in the air. These ants are predaceous, but are also omnivorous (feeding on seeds) and eat dead insects. They also tend Homoptera. (Mackay and Mackay 2002, Pacheco and Mackay 2013)

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

Pacheco and Mackay (2013) – Worker - This is a small, yellow species (occasionally pale brown), in which the dorsum of the head is finely punctated. The lateral clypeal teeth are well developed while the extralateral teeth are developed into small bumps. The minor funicular segments are typically about 0.14 mm in length. Queen - The queen is moderately large at just over 5.00 mm in total length and concolorous yellow to pale brown. The head and dorsum of the mesosoma are semi-coarsely punctate, with long yellow erect hairs projecting from them. The petiole and postpetiole are horizontally striated. The petiolar peduncle has a small flange ventrally. Male - The male is concolorous dark brown to bicolored with a brown head and gaster and yellow to golden brown body and is moderately large at just under 4 mm in total length. The anterior clypeal margin is convex. The frontal lobes are horizontally striated. The propodeum, petiole and postpetiole are horizontally striated. The petiolar peduncle has an angle ventrally (not a tooth or flange).

As most thief ant species are minute and concolorous yellow in color, it is difficult to differentiate S. molesta from other small species. It is often the case that any small, yellow species is incorrectly named S. molesta. However, Solenopsis molesta is the most common and widespread thief ant in the continental United States. When one collects a small, yellow Solenopsis, there is a high probability it is S. molesta. This common species can be separated from Solenopsis texana, Solenopsis carolinensis and Solenopsis abdita, by the longer length of the minor funicular segments. It can be separated from Solenopsis krockowi and its relatives, as the punctures on the head are much finer and the minor funicular segments are rarely greater than 0.150 mm in total length. It is difficult to separate the worker of Solenopsis validiuscula. Solenopsis molesta workers are often smaller than those of S. validiuscula (total length 1.80-2.00 mm). The cephalic punctures of S. validiuscula are moderately coarse, while S. molesta are finer. If queens are available, the queens of S. validiuscula are always dark brown, while S. molesta is typically concolorous yellow. The male of S. molesta is light brown and occasionally bicolored, while the male of S. validiuscula is concolorous dark brown. The pedicel of the male of S. molesta is large compared to that of the S. validiuscula male (length nearly as long as the scape). Although the two species are similar in size and form, based on the above differences in the castes, they will be recognized as different species.

It is difficult to separate the workers of S. molesta from ''S. texana. Solenopsis texana is consistently smaller, with the total length ranging from 1.20-1.30 mm. The queens of S. molesta are easily separated as they are much larger than those of S. texana (total length of S. molesta ranging from 4 - 5.5 mm, the queen of S. texana'' has a total length of slightly over 3 mm). The queen of S. molesta is yellow or pale brown; that of S. texana is black to dark brown.

The worker is easily confused with those of Solenopsis salina, as both species are yellow and have similar cephalic punctures. They can be separated as the minor segments of the funiculus of S. molesta are nearly always over 0.120 mm in length, those of S. salina are nearly always shorter than 0.100 mm in length. The clypeal teeth of S. molesta are nearly straight, whereas they are usually slightly incurved in S. salina.

Keys

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

Distribution
A wide range that includes southern areas of Canada, most of the continental US and northern Mexico.

Distribution based on Regional Taxon Lists
Nearctic Region: Canada, United States. Neotropical Region: Mexico.

Biology
Solenopsis molesta nests underground, often under stones, generally near the nests of other species where it steals from its host. Solenopsis molesta has been collected in nests of the following species, Myrmica americana, Manica invidia, Pogonomyrmex occidentalis, Pogonomyrmex montanus, Messor lobognathus, Monomorium minimum, Pheidole bicarinata, Pheidole pilifera, Dorymyrmex insanus, Camponotus vicinus, Lasius crypticus, Lasius neoniger, Lasius sitiens, Lasius umbratus, Lasius claviger, Lasius interjectus, Lasius murphyi, Formica argentea, Formica neogagates, Formica limata, Formica rubicunda, Formica bradleyi, Formica altipetens and Formica fusca. Colonies contain up to a few thousand workers. Reproductives and brood are present throughout summer to fall. It is occasionally polygynous, with up to eight queens in a single nest. Nuptial flights occur from late July to early fall. (Mackay and Mackay 2002, Pacheco and Mackay 2013)

Nomenclature

 *  molesta. Myrmica molesta Say, 1836: 293 (q.) U.S.A. Wheeler, G.C. & Wheeler, J. 1955c: 134 (l.); Petralia & Vinson, 1980: 383 (l.); Crozier, 1970: 116 (k.). Combination in Solenopsis: Mayr, 1863: 407; in S. (Diplorhoptrum): Creighton, 1950a: 237. Senior synonym of debilis, exigua, minuta: Emery, 1895c: 277; Emery, 1896g: 85.
 * minuta. Myrmica minuta Say, 1836: 294 (w.) U.S.A. Junior synonym of molesta: Emery, 1895c: 277.
 * exigua. Myrmica (Tetramorium) exigua Buckley, 1867: 342 (w.q.) U.S.A. Junior synonym of molesta: Emery, 1895c: 277. See also: Wheeler, W.M. 1902f: 28.
 * debilis. Solenopsis debilis Mayr, 1886d: 461 (w.q.m.) U.S.A. Junior synonym of molesta: Emery, 1895c: 277; Emery, 1896g: 85.

Worker
Pacheco and Mackay (2013) - Measurements (n=6). TL 1.38-1.62 (1.50); HL 0.420-0.510 (0.457); HW 0.360-0.432 (0.386); EL 0.036-0.042 (0.040); ED 0.030-0.036 (0.032); SL 0.282-0.348 (0.317); FSL 0.132-0.156 (0.141); CI 81.1-87.8 (84.5); SI 64.7-72.9 (69.4); PL 0.072-0.096 (0.083); PW 0.120-0.156 (0.126); PI 57.7-80.0 (66.3); PPL 0.102-0.120 (0.108); PPW 0.120-0.162 (0.135); PPI 74.1-85.7 (80.4); WL 0.300-0.342 (0.325); PSL 0.030-0.036 (0.032); PSW 0.030.

Small; concolorous yellow to pale brown; head longer than wide, sides nearly straight, finely punctate; lateral clypeal teeth well developed, extralateral teeth absent; clypeal carinae well defined; scape long, nearly reaching posterior lateral corner of head; minor funicular segments moderately long; eye small, 3-5 ommatidia; pronotum finely punctate, smooth and shiny between punctures; mesopleuron smooth and shiny; notopropodeal suture well depressed, notch-shaped, groove breaks sculpture of mesosoma; posterior border of propodeum rounded; propodeal spiracle small, round; metapleuron horizontally striated; petiole wider than postpetiole viewed laterally; petiolar peduncle with minute angle ventrally; postpetiolar node semicircular viewed laterally, lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; erect and suberect hairs covering all body surfaces; scape with numerous appressed hairs; dorsum of mesosoma with hairs of various lengths (0.060-0.120 mm); hairs on petiole, postpetiole and gaster curve posteriorly.

Queen
Pacheco and Mackay (2013) - Measurements (n=6). TL 4.68-5.64 (5.36); HL 0.720-0.840 (0.781); HW 0.642-0.780 (0.743); EL 0.240; ED 0.180; MOL 0.072-0.120 (0.103); MOD 0.072-0.120 (0.097); SL 0.516-0.540 (0.536); FSL 0.300; CI 89.2-98.5 (95.1); SI 64.3-71.7 (68.7); PSL 0.072-0.078 (0.075); PSW 0.060; PL 0.120; PW 0.276-0.384 (0.350); PI 31.3-43.5 (34.7); PPL 0.276-0.360 (0.306); PPW 0.330-0.420 (0.405); PPI 71.4-85.7 (75.8); WL 0.960-1.20 (1.12).

Moderately large; concolorous yellow to pale brown; head longer than wide, posterior border slightly concave, semi-coarsely punctate; lateral clypeal teeth well developed, extralateral teeth absent; clypeal carinae well defined; frontal lobes vertically striated; eyes large, extend 0.084 mm past lateral margin of head; scapes long, reach lateral ocelli; medial ocellus small, depigmented; dorsum of mesosoma semi-coarsely punctate, smooth and shiny between punctures; posterior propodeal margin viewed laterally slightly angled; propodeal spiracle small, oval; metapleuron horizontally striated; sides of petiolar and postpetiolar nodes horizontally striated; petiolar peduncle with thin flange ventrally; postpetiole lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; numerous erect and suberect hairs of various lengths on all body surfaces; hairs on dorsum of mesosoma long (0.120-0.180 mm); hairs on petiole and postpetiole long (up to 0.240 mm), curve posteriorly.

Male
Pacheco and Mackay (2013) - Measurements (n=6). TL 3.48-4.32 (3.85); HL 0.498-0.516 (0.504); HW 0.510-0.534 (0.518); EL 0.276-0.300 (0.282); ED 0.216-0.228 (0.225); MOL 0.078-0.108 (0.091); MOD 0.102-0.120 (0.111); SL 0.204-0.228 (0.212); FSL 0.960-1.02 (0.972); CI 102-104 (103); SI 40.7-44.7 (42.3); PSL 0.078-0.090 (0.083); PSW 0.060; PL 0.132-0.144 (0.138); PW 0.252-0.282 (0.266); PI 48.9-55.8 (52.1); PPL 0.240; PPW 0.300-0.360 (0.324); PPI 66.7-80.0 (74.4); WL 0.960-1.08 (1.05).

Moderately large; concolorous dark brown to bicolored (darker head and gaster than mesosoma); head smooth and shiny with scattered fine punctures, wider than long; anterior clypeal margin convex, lacking teeth or carinae; frontal lobes vertically striated, extend laterally then anteriorly to clypeal margin; antennae long, yellow; eyes large, extend 0.120 mm past lateral margin of head; medial ocellus large, lacking pigment; semi-coarse punctures on pronotum, smooth and shiny between punctures; posterior propodeal margin viewed laterally rounded; propodeal spiracle small, round; propodeum striated; petiolar node rounded dorsally, horizontally striated, peduncle lacking tooth or flange ventrally, but with angle; postpetiolar node flattened dorsally, horizontally striated, lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; erect and suberect hairs of various lengths covering all body surfaces; most hairs on pronotum about 0.120 mm in total length; hairs on petiole and postpetiole curve posteriorly.

Type Material
Pacheco and Mackay (2013) - None known to exist (type locality, Indiana). Apparently, none of the type series exist today. We picked the most common specimens that range near the type locality to anchor the identity of this species. Additionally, we knew the identity of closely related species.