Stegomyrmex vizottoi

Stegomyrmex vizottoi is the only species in the genus for which both sexes and castes are known. It has been registered from localities in northern Argentina, Paraguay, and states of Santa Catarina, Parana, and Sao Paulo, southeastern Brazil. (Feitosa et al. 2008)

Identification
Feitosa et al. (2008) - This species is uniquely characterized by the combination of relatively large size (TL ≥ 6.00 mm), mesosoma partially sculptured but for the lateral faces which are almost entirely smooth and shining, and propodeum relatively narrow in dorsal view.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil.

Biology
Feitosa et al. (2008) - Diniz and Brandao (1993) published observations on the foraging and nesting habits of Stegomyrmex vizottoi from Mirassol, Sao Paulo, Brazil. They observed that workers are specialized predators of spirobolid millipede eggs and forage solitarily, moving slowly in shaded areas, probing in small cracks and cavities in the soil. The ants seem to use their faces like a shovel, tucking their antennae in the antennal scrobes and pushing soil away with the face. When a millipede egg is found, it is grasped by the undersurface of the mandibles and pressed against the gular face of the worker’s head, which then returns to the nest. These ants are virtually unnoticed to the naked eye, not only because they forage individually, but because of their slow movements, and because as they age their integument becomes covered by a thin but hard layer of mud. Moreover, workers can feign death for several minutes when disturbed.

Diniz and Brandao (1993) were the first to examine a Stegomyrmex nest in detail. The S. vizottoi small and perfectly rounded nest entrance (0.4 cm in diameter) was in a vertical soil bank, leading to a single sinuous tunnel extending about 40 cm to a secondary chamber, in the roof of which they found a funnel leading to the main chamber. Along the tunnel, which had several small dead ends, they found three enlargements, where the returning workers apparently stop to clean the eggs before reaching the secondary chamber. The cleaning process continues at the secondary chamber, and the eggs are piled in the main chamber only when completely cleaned. The main chamber contained the colony dealate gyne, its brood and a pile of fully cleaned millipedes’ eggs. The secondary chamber contained the millipede egg shells, never found in the main chamber. The total worker population in this particular nest was 76. A second nest contained some 300 workers, 22 alate gynes, seven dealate gynes, and brood. Colonies transferred to gypsum laboratory nests with conditions and architecture similar to that of natural nests, adapted easily to the new conditions and even constructed the funnel-like structure linking the secondary to the main chamber. It is interesting to note that in the relatively mild winters in southeastern Brazil, populations of colonies decrease sharply even in the laboratory, and the ants close the nest’s entrance, relaying entirely on the millipede eggs collected in the previous season for nutrition during the winter time, the eggs being taken from the pile one at a time, to be consumed by all individuals arranged in a circle. This helps to make these ants unnoticed for several months a year, contributing to their rareness status.

Nomenclature

 *  vizottoi. Stegomyrmex vizottoi Diniz, 1990: 290, figs. 7-9, 11, 12, 18-21, 25-28, 32-35 (w.q.) BRAZIL. Feitosa, Brandão & Diniz, 2008: 76 (m.). See also: Diniz & Brandão, 1993: 301.

Description
Feitosa et al. (2008):

Worker
Holotype (N=7); HW 1.26 (1.17–1.33); HL 1.07 (1.00–1.14); ML 0.58 (0.51–0.61); SL 0.80 (0.76–0.85); WL 1.65 (1.59–1.77); PL 0.78 (0.70–0.80); PPL 0.46 (0.41–0.49); GL 1.60 (1.48–1.70); TL 6.14 (5.72–6.48); CI 118.18 (116.67–118.60); SI 63.46 (61.82–67.96). Dark brown to black, with ferruginous appendages. Mandible finely and densely striate, with large and sparse piligerous punctures, except for the masticatory border and dorsum of apical portion which are smooth and shining; inner surface of antennal scrobes feebly striate and with punctuation restricted to the region of antennal insertions; central disc of head and external margin of frontal lobes moderately areolate; oblique lateral grooves of head, frontal area and posterior portion of frontal lobes predominantly smooth and shining, with a few sparse punctures; anterior portion of frontal lobes weakly areolate and with irregular longitudinal rugulae; antennae opaque and finely punctate; lateral and ventral surfaces of head deeply areolate; occipital face of head mostly smooth and shining, except for the nucal collar which is uniformly scrobiculate; mesosoma partially foveolate, with the dorsum densely sculptured and the lateral surfaces mostly smooth and shining with a few sparse foveae; anterior coxae, petiole, and postpetiole entirely and deeply areolate-rugose; legs opaque and weakly sculptured; surface of gaster finely and deeply foveolate.

Pilosity cream-colored. Body covered by slightly stiffened, moderately clavate hairs, somewhat shorter in the external borders of frontal lobes, antennal scapes, and legs; mandibles with long, sparse filiform setae; posterior portion of ventral surface of head and anteroinferior portion of pronotum with short, curved, plumose hairs; occipital face of head and lateral surface of mesonotum, metanotum, and propodeumglabrous.

Head relatively broad in frontal view. Vertexal margin slightly convex and with a discrete concavity medially; eyes with circa six facets at maximum diameter.

Promesonotum relatively elongate in dorsal view, strongly convex dorsally in lateral view; promesonotal suture distinct only in the lateral faces of promesonotum; anepisternum set lower than the adjacent surface; metapropodeal groove large, shallowly impressed and without median projections; propodeal spines relatively short, subtriangular, with the apexes directed upwards and with the posterior faces straight; propodeal spiracles weakly projected posterad; propodeal lobes rounded and projected over the petiolar peduncle. In dorsal view, propodeum as narrow as the promesonotum.

Petiole elongate, slightly arched, with a long rounded node; ventral carina of peduncle with a well-developed anterior projection. Postpetiole globose, with the dorsal face gently convex, without ventral projections. Gaster oval and robust.

Sting apparatus: Spiracular plate subquadrate, not extending towards the medial connection; margin of medial connection sclerotized; dorsal notch present; spiracle moderately wide and placed close to the posteroventral region of plate; anterior apodema enlarged medially and with an apical tubercle; ventral edge well developed. Quadrate plate with the dorsal region broader than the ventral region, excluding the apodema; apodema area smaller than the plate body; dorsal margin flattened and sloped; anterodorsal corner of apex acute; posterior margin divided. Anal plate with the arc strongly sclerotized; apical margin triangular and well definite; anal sensillae equally developed and restricted to the posterior border of plate. Oblong plate with short posterior apodema; subterminal tubercle acute apically; postincision well developed. Gonostylus one-segmented and with five chaetae subequal in length; terminal sector short and membranous, with dorsoterminal and companion chaetae present. Triangular plate as long as broad; only the median tubercle is present. Lancets with functional valves; sensorial barbles absent; distal portion weakly sclerotized, probably not perforating; dorsal and ventral margins converging towards the apex; outer dorsal wall absent. Sting shaft weakly sclerotized, not perforating; dorsum of valve chamber indistinct in profile; internal apophysis long and well sclerotized, extending along the dorsum of valve chamber; basal connection strongly concave; anterolateral processes well developed, narrowed medially, and as broad as the furcula lateral arms; campaniform sensilla absent. Dorsal arm of furcula indistinct; lateral arms well developed; fulcral articulation connected to the sting basis only by its lateral corner.

Queen
(N=1); HW 1.46; HL 1.19; ML 0.65; SL 0.95; WL 2.00; PL 0.92; PPL 0.56; GL 1.99; TL 7.31; CI 122.45; SI 65.00. Like conspecific worker, with the modifications expected for myrmicine gynes. Plumose hairs restricted to the posteroventral corner of head and inferior corner of pronotum. Compound eyes with circa 13 facets at maximum diameter; propodeal spines reduced; posterior face of propodeum slightly inclined in side view, reaching the propodeal lobes in rounded angles. Forewing with strongly colored stigma; longitudinal vein Sc+R nebulous when reaching the stigma; SR extending distally beyond the stigma as a tubular vein for most of its length;Mand Cu also extending distally, initially as tubular veins and then as spectral veins almost reaching the distal wing border; anal vein not extending beyond CU cell. Hind wing with Sc+R extending shortly beyond the point where they connect to M, which extends as a spectral vein to the wing distal border; basallyM+Cu does not continue as a tubular vein beyond the junction with 1M; anal vein drastically reduced; seven submedian hamuli.

Male
(N=4); HW 0.92–0.98; HL 0.80–0.85; ML 0.21–0.24; SL 0.29–0.30; WL 1.89–2.04; PL 0.90–0.95; PPL 0.41–0.49; GL 1.82–1.89; TL 6.07–6.41; CI 114.29–115.15; SI 30.00–31.58. Slightly smaller and slenderer than conspecific gynes. Color black with appendages and gaster somewhat lighter. Integument opaque and densely areolaterugose, except for the postpetiole and gaster, which are smooth and shining; appendages very finely punctate. Dorsum of head and mesosoma densely covered by whitish, fine, suberect hairs, sparser over the dorsum of the metasoma; appendages with short, subdecumbent hairs.

Head broadest across large bulging compound eyes (situated at the head midlength) rather suddenly narrowed in front of eyes and tapering moderately anterad; median portion of vertexal margin weakly convex; occipital corners rounded; ocelli prominent. Mandible relatively developed, subtriangular, with slightly curved outer borders, rapidly converging in apical half; gently down curved; masticatory border bearing circa seven serial teeth, with the apical tooth much more developed than the others. Clypeus broad and truncate in front. Frontal lobes not so developed as in the conspecific gynes and workers, but concealing the antennal insertions. Frontal carinae short and not expanded laterally, forming a short and shallow antennal scrobe. Antennae long and slender with 13 segments; scape very short, only about twice as long as broad.

Prescutum with more or less distinct anteromedian carina; notauli shallow and complete, with transversal costulae. Parapsidial furrows as fine shining lines; parapsides more or less impressed behind, but each with a sharp, raised posterolateral margin. Prescutellum separated from scutellum by an impression bearing short longitudinal rugae. Scutellum narrow posterad. Metanotum narrow, with blunt median tumosity. Propodeum with dorsal face flat, steeply sloping posterad, and unarmed. Legs slender, middle and hind tibiae without apical spurs; tarsal claws slender and simple. Wings brownish, with opalescent bluish reflections; venation as in the gynes.

Petiole clavate, with anterior peduncle distinct and long, low, rounded node; anteroventral projection vestigial. Postpetiole as broad as long in dorsal view and slightly broader posteriorly than anteriorly, attached to gaster by almost its full width. Gaster somewhat elongate.

Type Material
Feitosa et al. (2008) - Holotype worker. BRAZIL: Sao Paulo, Mirassol x.1971 (J. L. M. Diniz) (JLMD code 361) (MZSP code 11.029) (examined).