Solenopsis johnsoni

Solenopsis johnsoni nests under stones. Nests are polygynous (>4 queens in type series). Specimens from Sierra Juarez locality were on a thistle in a grass meadow. We collected a nest under a stone in the state of Mexico in May that had a number of males. It was in a grassy area full of weeds next to the road. It was hazy and rained the previous night. The soil was a brown rocky loam with good drainage and the soil was wet. (Pacheco and Mackay 2013)

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

Pacheco and Mackay (2013) – Minor and major worker These ants are light yellow in color and are characterized by quadrate heads and with erect and suberect hairs on all body surfaces. The lateral clypeal teeth are well developed and the extralateral teeth are present, but not as sharp. The scapes are relatively long (0.3 70 mm in the major, 0.300 mm in the minor), the minor segments of the antennae are relatively long (total length 0.16 mm in the major, 0.12 mm in the minor). Queen The gyne is a solid dark yellow color, large, very hairy and with very coarse punctures. The hairs are the same length (0.15 mm) throughout the body. It has medium sized eyes (maximum diameter 0.12 mm) and a moderately small ocellus (0.09 mm).

There are very few dimorphic species of thief ants. Solenopsis johnsoni is the only such species that we found in North America. It is easily recognized by its large size, coarsely punctate head and large ventral tooth present on the subpeduncular process.

The minor worker is nearly identical to the worker of Solenopsis melina. They can be separated as the subpeduncular process of S. johnsoni is in the form of a tooth, but is more of a flange in S. melina. The dorsum of the head (as seen in side view) of the minor worker of S. johnsoni generally has fewer than 10 erect hairs, whereas the head of the worker of S. melina in the same view has more than 20 erect hairs.

The queen is easily recognized as it has striae extending from the frontal lobes to the medial ocellus and is coarsely punctate on all body surfaces, including the scapes, mesosoma, petiole, postpetiole, in addition to the dorsum of the head. It can be easily separated from the queen of S. melina as it is much larger (total length > 5 mm) as compared to the smaller S. melina queen (TL<5 mm).

Keys

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

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Nomenclature

 *  johnsoni. Solenopsis johnsoni Pacheco, Mackay & Moreno, in Pacheco & Mackay, 2013: 193, figs. 132-137, map 31 (w.q.) MEXICO.

Worker
Minor. Measurements (n=2). TL 1.44; HL 0.420-0.444 (0.432); HW 0.360-0.384 (0.372); EL 0.030; ED 0.024-0.030 (0.027); SL 0.300; FSL 0.120-0.132 (0.126); CI 85.7-86.5 (86.1); SI 67.6-71.4 (69.5); PL 0.084-0.090 (0.087); PW 0.120-0.126 (0.123); PI 66.7-75.0 (70.8); PPL 0.108; PPW 0.126-0.138 (0.132); PPI 78.3-85.7 (81.9); WL 0.306-0.318 (0.312); PSL 0.030-0.036 (0.033); PSW 0.030.

Small; concolorous pale yellow; head quadrate, slightly longer than wide, sides of head straight, posterior border slightly concave; lateral clypeal teeth well developed, medial tooth absent, extralateral teeth small, angulate; clypeal carinae well defined; scape extends slightly more than 2/3 length of head; eye small, brown, at least three ommatidia; pronotum and mesopleuron smooth and shiny; lower mesopleural region slightly horizontally striated; petiole arched, peduncle with well-developed tooth ventrally; postpetiole oval, lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; hairs of various lengths (~0.030-0.150 mm), erect and suberect hairs on head, antennae hairy, scape with few suberect hairs, pronotal erect hairs projecting above outline viewed laterally, mesonotum with erect hairs (0.12mm) above profile; all hairs pointing in different directions.

Major. Measurements (n=4). TL 1.92-2.52 (2.24); HL 0.540-0.624 (0.591); HW 0.480-0.570 (0.525); EL 0.036-0.042 (0.041); ED 0.030-0.036 (0.035); SL 0.360-0.420 (0.386); FSL 0.162-0.198 (0.177); CI 85.0-91.3 (88.8); SI 60.0-67.3 (65.2); PL 0.120; PW 0.156-0.186 (0.171); PI 64.5-76.9 (70.5); PPL 0.150; PPW 0.168-0.198 (0.185); PPI 75.8-89.3 (81.8); WL 0.390-0.480 (0.439); PSL 0.036-0.048 (0.041); PSW 0.036-0.042 (0.038).

Moderately large; concolorous honey yellow; head longer than wide, sides convex; lateral clypeal teeth well developed; extralateral teeth angulate; clypeal carinae well defined; frontal lobes vertically striated; eyes small, 3-5 ommatidia; scapes long, reaching ¾ length of head; minor funicular segments 3-8 long; pronotum coarsely punctate, smooth and shiny between punctures; mesopleuron smooth and shiny; propodeal spiracle small; metapleuron horizontally striated; petiolar node triangular, round, peduncle with well-developed tooth ventrally; postpetiolar robust, semicircular, lacking tooth or flange ventrally.

Abundantly hairy, erect and suberect hairs of various lengths covering all body surfaces; most hairs long (0.120-0.150 mm).

Queen
Measurements (n=3). TL 5.40-5.88 (5.64); HL 0.780-0.804 (0.794); HW 0.816-0.840 (0.832); EL 0.270-0.282 (0.278); ED 0.210-0.228 (0.220); MOL 0.072-0.078 (0.076); MOD 0.084-0.090 (0.086); SL 0.558-0.570 (0.562); FSL 0.300-0.330 (0.320); CI 104-105 (104); SI 69.4-71.5 (70.8); PSL 0.084-0.096 (0.090); PSW 0.066-0.084 (0.072); PL 0.144-0.150 (0.146); PW 0.378-0.390 (0.384); PI 36.9-39.1 (38.0); PPL 0.300; PPW 0.360; PPI 83.3; WL 1.32-1.44 (1.38).

Large; concolorous dark yellow; head quadrate, coarsely punctate; lateral clypeal teeth well developed; extralateral teeth small, well developed; clypeal carinae well defined; frontal lobes vertically striated, with striae extending up dorsum of head to medial ocellus; scapes long, coarsely punctate, reaching ¾ length of head; minor funicular segments 3-8 long; eyes black, large; medial ocellus moderately small, round; mesosoma coarsely punctate; mesopleuron horizontally striated; petiolar peduncle with flange ventrally.

Abundantly hairy, pilosity yellow; most hairs arising from coarse punctures, most hairs long (0.180-0.210 mm) on all body surfaces.

Type Material
Holotype 21, 11 paratype unknown symbol worker and 3 paratype queens,. Mexico, Baja California Sur, 0.4 mi Sierra San Francisco, 3610 feet, 26-i-1995, R Johnson #BCS 1201.

Etymology
Named to honor our friend and fellow myrmecologist, Dr. Robert Johnson, who collected the type series, as well as a large number of other interesting species.