Lachnomyrmex pilosus

Individuals are commonly encountered in the leaf litter of wet forests, from lowland to submontane areas (200–1430m).

Identification
Feitosa and Brandão (2008) - Body irregularly rugose; metanotal groove narrow and deeply impressed; apex of propodeal spines curved upwards; petiolar node rounded dorsally; dorsum of petiolar node and postpetiole each with more than 10 long hairs; first tergite of gaster entirely covered by long flexuous hairs. The smaller size and well defined metanotal groove separate this species from the related Lachnomyrmex laticeps. Although the workers of L. pilosus and Lachnomyrmex scrobiculatus are easily distinguishable, the gynes of these species are quite similar. Gynes of L. pilosus can be separated from L. scrobiculatus by the rounded petiolar node and by the absence of an anteroventral process on the postpetiole.

There is considerable geographical variation among specimens of L. pilosus, mainly in body size. Individuals collected in the eastern Amazon Basin are relatively small, while specimens from central Brazil and Peru are usually large. Intermediate forms can be found in the remaining localities of northern South America.

Distribution based on Regional Taxon Lists
Neotropical Region: Bolivia, Brazil, Colombia, Ecuador, Grenada, Peru, Trinidad and Tobago, Venezuela.

Nomenclature

 *  pilosus. Lachnomyrmex pilosus Weber, 1950c: 1 (w.) TRINIDAD. Feitosa & Brandão, 2008: 31 (q.).

Description
Feitosa and Brandão (2008):

Worker
Holotype HL 0.70; HW 0.68; ML 0.24; SL 0.43; EL 0.16; WL 0.77; PSL 0.16; PL 0.30; PPL 0.17; GL 0.92; TL 3.10; CI 97; SI 63; OI 24. Worker measurements (n=30). HL 0.54–0.72; HW 0.55–0.72; ML 0.18–0.26; SL 0.46–0.35; EL 0.11– 0.17; WL 0.60–0.85; PSL 0.13–0.20; PL 0.25–0.35; PPL 0.18–0.13; GL 0.66–0.96; TL 2.37–3.30; CI 93–102; SL 59–70; 19–27. Color light reddish-brown to dark brown, with appendages lighter. Body densely covered by vermiculate short rugae, forming irregular areolae on promesonotum; rugae somewhat longer and longitudinal on head dorsum and slightly sparser on mesopleura and lateral surfaces of propodeum; mandibles with short striae restricted to basal portion; petiole and postpetiole irregularly rugose. Abundant pilosity, except by dorsal surface of propodeum; dorsum of petiolar node and postpetiole and first gastral tergite densely covered by long flexuous hairs. Head as long as broad to longer than broad, with vertexal margin relatively short and only weakly convex; frontal lobes rounded laterally; eyes with about seven facets on maximum diameter. Promesonotum considerably convex in profile; metanotal groove narrow and deeply impressed; apex of propodeal spines curved upwards; teeth of propodeal lobes well developed, reaching propodeal spines half-length. Petiolar node elevated and rounded dorsally in lateral view; postpetiole moderately convex and with sternite only feebly projected.

Queen
(n=7). HL 0.60–0.73; HW 0.57–0.73; ML 0.20–0.25; SL 0.35–0.49; EL 0.16–0.21; WL 0.76–1.04; PSL 0.15–0.20; PL 0.31–0.39; PPL 0.16–0.19; GL 0.94–1.10; TL 2.98–3.71; CI 96–100; SI 60–66; OI 27–30.

Eyes with about 13 facets at greatest diameter; wings with the basic pattern of venation for the genus; bases of propodeal spines with around five long flexuous hairs; petiolar peduncle slightly longer than in the conspecific workers, with a discrete anteroventral tooth.

Larva
Feitosa and Brandão (2008), after Wheeler & Wheeler 1989 - Length (through spiracles) 2.4–2.9mm. Head hairs 0.038–0.125mm long, scarce (about 25), shaft curved and smooth. Body hairs very sparse, long, generally distributed. Fours types present: (1) 0.06–0.10mm long, with slightly curved shaft and short frayed tip, on ventral half of body; (2) 0.125–0.3mm long, with curved shaft and small apical bulb, on dorsal half of body; (3) about 0.016mm long, few, smooth, with flexuous shaft and uncinate tip; and (4) 0.19–0.22mm long, with flexuous shaft, anchor-tipped, four hairs in a transversal row across dorsum of abdominal segments I–III and V, and six on abdominal segment IV. Cranium subhexagonal, slightly wider than long, dorsal border feebly concave. Antennae at midlength of cranium, large, three closely spaced sensilla on a sclerotized slight elevation on a feebly stained, large raised teardrop-shaped base. Maxilla small with abruptly narrowed apex; palp and galea subequal in height; palp subcylindical with five (two apical with a spinule each, two large subapical and encapsulated, and one lateral with a rather long spinule) sensilla; galea subconical with two apical sensilla. Labrum small, bilobed, anterior surface with 12 sensilla on and near the ventral surface; ventral surface with minute spinules in the impression; posterior surface spinulose, the spinules coarse an isolated, with about 20 sensilla; anterior surface of labrum with short transverse rows of rather long spinules; palp short paxilliform, with five sensilla similar in length to maxillary sensilla; sericteries opening as a short transverse slit in a slight depression. Hypopharynx with a few short transverse rows of minute spinules dorsally. Mandibles heavily sclerotized laterally and apically, blade less sclerotized; apical tooth narrow and curved medially; blade with a rather stout-based apical tooth, a smaller subapical tooth, and a few denticles near teeth. Body with few distinct somites. Spiracles small, decreasing slightly posteriorly. Integument on venter of thoracic segments I–III and abdominal segments I–III with a few minute spinules; abdominal segments VII–X more spinulose.

Etymology
Feitosa and Brandão (2008) - Weber (1950) certainly named this species after its abundant pilosity. From Latin, pilosus: hairy.

Determination Clarifications
In the description of Lachnomyrmex larvae (Wheeler & Wheeler 1989) and in the first record of the genus for Venezuela (Lattke 1991), the authors refer to the examined specimens as L. scrobiculatus. However, we have studied the material mentioned in both studies and concluded that these specimens actually belong to L. pilosus.

References based on Global Ant Biodiversity Informatics

 * Feitosa, R.M. and C.R.F Brandao. 2008. A taxonomic revision of the Neotropical myrmicine ant genus Lachnomyrmex Wheeler (Hymenoptera: Formicidae). Zootaxa 1890:1-49
 * Fernández, F. and S. Sendoya. 2004. Lista de las hormigas neotropicales. Biota Colombiana Volume 5, Number 1.
 * Fichaux M., B. Bechade, J. Donald, A. Weyna, J. H. C. Delabie, J. Murienne, C. Baraloto, and J. Orivel. 2019. Habitats shape taxonomic and functional composition of Neotropical ant assemblages. Oecologia 189(2): 501-513.
 * Franco W., N. Ladino, J. H. C. Delabie, A. Dejean, J. Orivel, M. Fichaux, S. Groc, M. Leponce, and R. M. Feitosa. 2019. First checklist of the ants (Hymenoptera: Formicidae) of French Guiana. Zootaxa 4674(5): 509-543.
 * Groc S., J. H. C. Delabie, F. Fernandez, M. Leponce, J. Orivel, R. Silvestre, Heraldo L. Vasconcelos, and A. Dejean. 2013. Leaf-litter ant communities (Hymenoptera: Formicidae) in a pristine Guianese rainforest: stable functional structure versus high species turnover. Myrmecological News 19: 43-51.
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * Weber N. A. 1950. New Trinidad Myrmicinae, with a note on Basiceros Schulz (Hymenoptera, Formicidae). Am. Mus. Novit. 1465: 1-6.