Solenopsis saevissima

A South American fire ant that utilizes disturbed habitats and has been introduced to areas beyond its native range.

Identification
S. saevissima may be easily distinguished from both Solenopsis invicta and Solenopsis richteri by the characters given in the descriptions and figures. The major points in the separation of saevissima from invicta are in the habitus of the head, the thoracic shapes in major workers, the proportions of the postpetiole, the differences in sculpturing, and the differences in color in major workers. S. richteri and saevissima are not likely to be confused because of the strong differences in color. They are also different in many other ways including head shape, thoracic structure, and sculpturing. (Buren 1972)

Pitts et. al. (2018) - This species is highly variable in both coloration and size of the workers and gynes. They range from the small dark forms in southern Brazil to the large orange brown forms in northern Brazil. These color forms are not morphologically distinct, however, as there is an almost continuous cline in size and coloration. Recently, Ross et al. (2010) were able to distinguish five evolutionary independent lineages in nominal S. saevissima using genetic data. Discovery of differentiating characters and formal description of these putative species is still outstanding.

The gynes of S. saevissima lack mesonotal maculae like Solenopsis electra, Solenopsis pusillignis, and Solenopsis macdonaghi. Contrary to this, some callow gynes have integumental maculations on the mesonotum. These maculations are not distinctly margined and must fade as the gyne matures.

There is a large size variation of the males as well. However, the distribution is opposite to that of the workers and gynes. The larger males are normally found within colonies of the smaller, dark-form workers.

Males of S. saevissima are most similar to S. pusillignis due to their lighter coloration and to the region of the head posterior to the ocellar triangle being glabrous. The males of S. saevissima lack the large ocelli and mesonotal maculations possessed by males of S. pusillignis. Males of S. saevissima tend to have the OOI (2.50–3.50) larger than any other species (<2.70).

The larvae of S. saevissima are similar to Solenopsis invicta. Although S. saevissima larvae normally have a smaller head capsule than S. invicta, the setal characters are similar between the two species. Some larval specimens of S. saevissima have denticulate setae present on the body, which differs from S. invicta.

Distribution
Pitts et. al. (2018) - A light color variant of S. saevissima occurs throughout the Amazon basin. The dark color variant occurs south from Goais and Bahia to Sao Palo State in Brazil. The dark color variant occurs sporadically throughout the Amazon basin.

Distribution based on Regional Taxon Lists
Afrotropical Region: Guinea. Neotropical Region: Argentina, Bolivia, Brazil, Ecuador, French Guiana, Guyana, Paraguay, Suriname, Uruguay.

Habitat
In French Guiana Solenopsis saevissima is found in riparian forest, forest edges, and meadows. Riparian forest is likely its native habitat and this species is commonly found along naturally disturbed riverbanks of the Amazon Basin. Solenopsis saevissima is also able to quickly colonize areas of rainforest disturbed by man. (Dejean et al. 2015)

Biology
Pereira et al. (2017) - An experimental test showed this ant could delay composition of carcasses. This occurred through delaying the colonization of decomposers via the ant's aggressive defense of food, i.e., carcasses, that they were actively foraging upon. Pitts et. al. (2018) - As is the case with S. invicta and S. richteri, extreme genetic differentiation of geographic populations of S. saevissima has been detected using mtDNA sequence data as well as nuclear microsatellite data (Shoemaker et al. 2006, Ross et al. 2010). In particular, specimens from Amazonian, southeastern Atlantic, and south-central Atlantic portions of the Brazilian range are highly divergent from specimens collected in central Brazil. The various color forms in this species are not concordant with the major genetic lineages.

Associations with other Organisms
S saevissima is parasitized by numerous species of Phorid Flies.

Nomenclature

 *  saevissima. Myrmica saevissima Smith, F. 1855c: 166, pl. 13, fig. 18 (w.) BRAZIL. Combination in Solenopsis: Mayr, 1862: 751. Goni, Zolessi & Imai, 1983: 365 (k.). Junior synonym of geminata: Mayr, 1865: 109; Mayr, 1886d: 460; Dalla Torre, 1893: 76. Revived from synonymy as subspecies of geminata: Wheeler, W.M. 1915b: 395. Revived status as species: Mann, 1916: 447; Santschi, 1916e: 378; Santschi, 1923c: 265; Creighton, 1930b: 80. Senior synonym of gracilior: Creighton, 1930b: 80; of moelleri (and its junior synonyms incrassata, morosa), perfida: Wilson, 1952b: 55. Material of the unavailable name picea referred here by Trager, 1991: 189. Current subspecies: nominal plus itinerans. See also: Buren, 1972: 15; Trager, 1991: 188.
 * gracilior. Solenopsis moelleri var. gracilior Forel, 1904d: 174 (w.) BRAZIL. Junior synonym of saevissima: Creighton, 1930b: 80.
 * moelleri. Solenopsis moelleri Forel, 1904d: 173 (w.q.m.) BRAZIL. Subspecies of saevissima and senior synonym of incrassata, morosa: Creighton, 1930b: 83. Junior synonym of saevissima: Wilson, 1952b: 55.
 * incrassata. Solenopsis geminata var. incrassata Forel, 1908c: 362 (w.) BRAZIL. Subspecies of pylades: Forel, 1909a: 268; of saevissima: Gallardo, 1919b: 247. Junior synonym of moelleri: Creighton, 1930b: 83.
 * morosa. Solenopsis saevissima var. morosa Santschi, 1916e: 380 (w.) BRAZIL. Santschi, 1923c: 265 (q.). Junior synonym of moelleri: Creighton, 1930b: 83.
 * perfida. Solenopsis saevissima var. perfida Santschi, 1923c: 266 (w.) BRAZIL. Junior synonym of saevissima: Wilson, 1952b: 55.

Type Material
Pitts et. al. (2018) - Syntype ? worker. Brazil. Para State. Tapajo´s. Bates. .

Worker
Buren (1972) - Head length .76 to 1.36 mm, width .64 to 1.37 mm; about 1.27 to 1.36 mm long, and 1.22 to 1.37 mm wide in majors. Scape length 1.00 to 1.04 mm in majors. Thoracic length 1.63 to 1.75 mm in majors.

Head wider behind the eyes as in Solenopsis invicta but lacking the subcordate appearance, occipital lobes not well developed, and occipital excision weak. Sides of head weakly convex, sometimes nearly straight. Scapes reaching or nearly reaching peaks of occipital lobes in majors. Pronotum with weakly to moderately developed shoulders in majors. Promesonotal suture always very weak, even in majors; pronotal surface anteromedially to this suture may be flattened, but never appearing actually sunken as in Solenopsis richteri. Promesonotum in profile rather evenly and moderately convex. Base of propodeum straight or very weakly convex and longer than the declivity. Petiole with a high, ovate scale, usually as wide or nearly as wide as narrow postpetiole; postpetiole little if any wider than long except in larger majors; in posterodorsal view postpetiole in majors with convex anterior border and straight sides. Transverse impression or rear dorsal surface of postpetiole often distinct.

In medium and small sized workers, head wider in front than behind; scapes reaching or surpassing hind borders of head; pronotum without trace of humeri or flattened area; postpetiole small, with sides slightly converging to rear but maintaining approximate equality in length to width ratio.

Sculpture weakly etched, most surfaces smooth and shining; genae with weak, irregular striae in front of eyes; piligerous punctures weak and inapparent on nearly all surfaces; striate area of mesopleura consisting of very fine and usually weakly etched striae, in very large workers these occasionally somewhat obliterated; wide smooth shining areas usually apparent on all sides of propodeal spiracle. Sculpture nearly absent on petiole, rear face of scale appearing free of shagreen throughout the size range. Postpetiole in major workers with subopaque areas on sides caused by minute puncturing; posterodorsal face largely smooth and shining even in majors; some weak transverse punctostriae largely confined to small area behind transverse impression; in very large majors dorsal surface may be somewhat shagreened, a few punctostriae may occur in front of impression.

Pilosity not appreciably different from that of richteri and invicta, possibly a little sparser than in those species.

Colors largely pale to darker yellow or light yellowish brown in medium to large workers; small workers may show considerable infuscation. The color may fade with time in preserved specimens.

Mandibles and often antennae dark brown and distinct from yellowish head; occiput and vertex faintly to more definitely banded with brown. Thorax and large spot on 1st segment of gaster yellowish to yellowish brown in large workers. Remainder of gaster brown. Petiole, postpetiole, and legs usually a little darker in color. Medium and small workers with gastric spot usually absent, thorax and rear third or more of the head considerably darker in some workers. No median dark mark on front of head, contrasting with the condition in invicta.

Pitts et. al. (2018) - Head subquadrate to weakly ovate. Head sculpture with small piligerous foveolae, <0.01 mm in diameter. Median frontal streak absent. Median ocellus in largest major workers absent. Mandibular costulae present throughout. Mesonotum with 20–25 setae. Promesonotal suture in largest major workers gently curved medially, never projecting upward. Mesonotum weakly convex in lateral view. Propodeum sculpture glabrous posteroventral to spiracle. Postpetiole shape as high as or higher than broad. Postpetiole sculpture in posterior view with lower 0.33–0.50 transversely rugose, upper surface glabrous and shiny. Color generally red brown to dark brown.

Queen
Pitts et. al. (2018) - Head. Slightly broader than long, quadrate, sides of head convex from eyes to occipital angles, straight to nearly straight ventral to eyes. Eye sometimes with 3–4 setae protruding from between ommatidia, setal length ≤ 3X width of ommatidium. Median ocellus large, circular. Lateral ocelli moderate to large, slightly ovate. Clypeus projecting, carinal teeth stout and sharp, carinae well defined, less so dorsally, slightly divergent ventrally. Paracarinal teeth small, sometimes poorly defined. Median clypeal tooth poorly developed, usually absent. Approximately 0.50 of eye dorsal to midpoint of head.

Mesosoma. Parapsidal lines present on posterior 0.50 of disk. Mesonotum with indistinct, median furrow on posterior one-sixth or less. Median bidentate process present on metasternum. Wing venation as in Figs.

Metasoma. Lateral faces of postpetiole weakly to strongly concave. Petiolar and postpetiolar spiracles tuberculate in some cases.

Coloration, Sculpturing, and Pilosity. Piligerous foveolae small, sparse, width <0.01 mm in diameter, larger on head than on thorax and abdomen. Pubescence simple, golden and erect, longer and denser on head than elsewhere, longest on anterior edge of clypeus. Mesosoma with longest pubescence (length >0.30 mm) 2X longer than shortest pubescence. Mandible with 9–11 fine, distinct costulae present throughout. Propodeum with fine striae posteriorly, anterior 0.25 polished. Posterior surface of petiolar node with lower 0.75 of surface with fine striae, dorsum polished. Posterior surface of postpetiolar node with lower 0.75 of surface with coarse striae, 4–7 striae present, median striae weak to obsolescent laterally, dorsum polished. Remaining integument smooth and polished. Color varies from dark brown to pale yellow on front of head, lateral portions of mesonotum, mandibles, mesosternum, appendages and apical portions of gaster segments. Color brown on vertex, interior margins of ocelli, medial area of mesonotum, parapsidal lines, lateral margins of T1 and preapical transverse areas on metasomal segments. Internal margins of ocelli dark brown. Median streak absent.

L ~7.1–8.0,HW1.3–1.8,VW0.5–0.9, HL 1.2–1.3, EL 0.4–0.6, OD 0.1–0.2, OOD 0.15–0.25, LOW 0.08–0.15, MOW 0.13–0.16, CD 0.15–0.22, MFC 0.20–0.25, EW 0.25–0.40, SL 0.89–1.12, PDL 0.18–0.25, LF1 0.1–0.14, LF2 0.07–0.1, LF3 0.07–0.12, WF1 0.09–0.12, FL 1.00–1.2, FW 0.19–0.31, MW 1.32–1.43, DLM 2.53–2.81, PRH 0.98–1.10, PL 0.58–0.82, PND 0.51–0.61, PH 0.52–0.83, PPL 0.28–0.43, DPW 0.48–0.83, PPW 0.60–0.91, PHB 0.27–0.51, N=13.

Male
Pitts et. al. (2018) - Head. Eye normally without setae protruding from between ommatidia. Ocelli large and prominent, elliptical.

Mesosoma. Propodeum rounded, declivous face perpendicular, flat except with distinct to indistinct median longitudinal depression, basal face strongly convex transversely and longitudinally. Metapleuron sometimes not broad, ~0.33 as wide as high, but usually broader, sometimes with transverse posterior carina. Wing venation as in Figs.

Metasoma. In cephalic view, dorsum of node varies from transverse to bilobate with deep median impression. Petiolar and postpetiolar spiracles distinctly tuberculate to not tuberculate. Genitalia as in Figs.

Coloration, Sculpturing, and Pilosity. Pubescence short, thin, yellow, erect to suberect and of uniform length over body (0.15–0.20 mm), longest on gena and vertex. Mesonotal pubescence sparse. Propodeum with base striato-granulate, medially finely granulate. Area between eye and insertion of antenna, area between ocelli, posterior portion of metapleuron, and base of petiolar nodes granulate to weakly granulate. Vertex posterior to ocellar triangle glabrous. Gena weakly striate. Posterior surface of petiolar node with lower 0.25 of surface with fine striae, lower 0.50 of surface granulate, sometimes granulations obsolescent medially, dorsum polished. Lateral faces of the scutellum striate. Remaining integument smooth and polished. Color generally red yellow to yellow brown. Antennae and legs pale yellow. Mandibles yellow.

L ;6.0–7.5, HW 0.89–1.10, VW 0.28–0.51, HL 0.70–0.81, EL 0.40–0.62, OD 0.05–0.11, OOD 0.18–0.32, LOW 0.10–0.22, MOW 0.15–0.25, CD 0.15–0.25, MFC 0.15–0.21, EW 0.30–0.40, SL 0.15–0.20, SW 0.09–0.15, PDL 0.05–0.12, PEW 0.09–0.15, LF1 0.10–0.21, LF2 0.10–0.15, LF3 0.15–0.20, WF1 0.09–0.10, FL 1.00–1.12, FW 0.15–0.21, MW 1.18–1.64, DLM 2.10–2.82, PRH 0.77–1.12, PL 0.50–0.61, PND 0.38–0.60, PH 0.30–0.61, PPL 0.18–0.44, DPW 0.40–1.03, PPW 0.43–0.94, PHB 0.30–0.40, N=12.

Larva
Pitts et. al. (2018) - Fourth instar worker larva.—Head. Large, subpyriform in anterior view (height 0.40 mm, width 0.43 mm). Cranium slightly broader than long. Antenna with 3 sensilla, bearing spinule. Occipital setal row with 4–8 bifid setae, base 0.5–0.66X total length of seta, 0.03–0.07 mm long. First setal row on vertex with 2 bifid setae, base ;0.66X total length of seta, setae 0.03–0.07 mm long. Second setal row on vertex with 4 setae, inner 2 setae simple, outer 2 setae with denticulate to bifid apices, 0.09–0.10 mm long. Setae ventral to antenna level simple, 0.12–0.14 mm long. Clypeus with transverse row of 4 setae, inner setae shorter than outer setae, 0.03–0.09 mm long. Labrum small, short (breadth 2.3X length). Labrum with 4–6 sensilla on dorsal surface of each half and apex with coarse isolated spinules. Each half of epipharynx with 2–3 isolated and 2 contiguous sensilla. Straight medial portion of mandible with 2–5 teeth that decrease in size dorsally. Maxilla with apex conical, palpus peg-like with 5 sensilla, 2 with spinules. Galea conical with 2 apical sensilla, each bearing one spinule. Labium with patch of spinules dorsal to each palpus, spinules coarse and isolated or in short rows of 2–3. Labial palpus slightly elevated with 4–5 sensilla, each bearing one spinule.

Body. Spiracles small, first spiracle slightly larger than others. Body setae of 2 types. Simple to denticulate setae (0.05–0.13 mm long) arranged in transverse row of 6–8 on ventral surface of each thoracic somite and on each of 3 anterior abdominal somites. Bifid setae (0.05–0.08 mm long) occur elsewhere, base ~0.5X length.

Length. Approximately 2.3 mm.