Lachnomyrmex pilosus Weber, 1950

Feitosa, Rodrigo M. & Brandão, Carlos Roberto F., 2008, A taxonomic revision of the Neotropical myrmicine ant genus Lachnomyrmex Wheeler (Hymenoptera: Formicidae), Zootaxa 1890, pp. 1-49: 31-33

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Lachnomyrmex pilosus Weber, 1950


Lachnomyrmex pilosus Weber, 1950 

Figures 1View FIGURE 1, 12, 18

Lachnomyrmex pilosus Weber, 1950: 1  . Holotype worker, TRINIDAD: British West Indies, Macqueripe Bay, 5.viii. 1935, N. Weber col., no. 260 [ AMNH] (examined); Wheeler & Wheeler 1989: 321 (larvae description, as L. scrobiculatus  ); Lattke 1991: 60 (first record for Venezuela, as L. scrobiculatus  ).

Worker diagnosis. 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.

Holotype measurements. 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.

Gyne measurements (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.

Worker description. 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.

Gyne (first description). Eyes with about 13 facets at greatest diameter; wings with the basic pattern of venation for the genus ( Fig. 1View FIGURE 1); bases of propodeal spines with around five long flexuous hairs; petiolar peduncle slightly longer than in the conspecific workers, with a discrete anteroventral tooth.

Mature larva (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. Weber (1950) certainly named this species after its abundant pilosity. From Latin, pilosus  : hairy.

Comments. The smaller size and well defined metanotal groove separate this species from the related L. laticeps  . Although the workers of L. pilosus  and L. 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.

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  .

Lachnomyrmex pilosus  occurs in Trinidad and central-northern South America, including many localities in northern Brazil, Bolivia, Colombia, Ecuador, Peru, and Venezuela. Individuals are commonly encountered in the leaf litter of wet forests, from lowland to submontane areas (200–1430m).

Additional material examined. BRAZIL: Amazonas: Manaus, iii-iv. 1994, R. Didham col. (12 workers) [ BMNH]; 20.x. 1994, A.B. Casimiro col., no. 4832 (1 gyne) [ CPDC]; Amapá: Macapá, Rod. Duque de Caxias, Km 9, 19.x. 1997, J.M. Vilhena col., no. 261 (1 worker) [ INPA]; Pará: Marituba, 1 º 22 ’S 48 º 20 ’W, 22.x. 2004, J.R.M. Santos col. (1 worker) [ CPDC]; Melgaço, Caxiuanã, 1 º 42 ' 23 ''S 51 º 27 ' 32 "W, 30.x. 2003, A.Y. Harada, E.P. Fagundes, C.E.D. Sanhudo, C.A.R. Moura & J.L.P. Souza cols (1 worker) [ INPA]; 23– 25.i. 2004, A.Y. Harada, E.P. Fagundes, C.E.D. Sanhudo & Joca cols (4 workers) [ MPEG]; Tocantins: Novo Jardim, 11 º 50 ' 26 ''S 46 º 41 ' 11 ''W, 9.x. 2004, R.R., Silva & B.H. Dietz (2 workers) [ MZSP]; BOLIVIA: Cochabamba: Lagunitas, 109km E Cochabamba, 1.ii. 1999, R. Anderson col., no. 18644 (2 workers) [ WPMC]; COLOMBIA: Amazonas: Araracuara, Cor. via Putumayo, 10.vii. 1994, G. Ganghi col., nos. 72098 / 72100 (2 workers) [ IHVL]; Meta: R. Neeva, Rod. Vallaro, 15.v. 1977, D. Jackson col. (1 worker) [ BMNH]; Nariño: Orito, Território Kofan, 00º 30 'N 77 º 13 'W, 25–28.ix. 1998, E. L. González col., nos. 72101–72108 (11 workers and 1 gyne) [ IHVL]; same data, nos. 72109 / 72110 (2 workers) [ MZSP]; ECUADOR: Morona Santiago: Los Tayos, 3.vii. 1976, Tjitte de Vries col. (1 gyne) [ MZSP]; Napo: Limoncocha, 00º 24 'S 76 º 36 'W, 12.viii. 1973, L. Morales col., no. 304 (1 worker) [ MZSP]; PERU: Amazonas: Ramón Castillo, 5km NW Letícia, 23.ii. 1972, S. Peck & J. Peck cols (2 workers) [ MZSP]; Cuzco: Campamento Cashiriari, 11 º 51 ' 1 "S 72 º 46 ' 45 "W, 15– 1997, J. Santisteban et al. cols, nos. 0201596/0201597 (2 workers) [ MUSM]; Madre de Díos: Los Amigos Field Station, Huangana, 12 º 34 ' 8 "S 70 º 6 ' 3 "W, 6–9.x. 2004, T.R. Schultz, C. Marshall & J. Sosa-Calvo cols, nos. 446595–446597 (3 workers) [ USNM]; TRINIDAD: Blue Basin, 1972, B. Pitkia col. (1 worker) [ BMNH]; VENEZUELA: Bolívar: Campamento Río Grande, 08º07'N 61 º 42 'W, 14.viii. 1986, P.S. Ward col., no. 8571.4 (1 worker) [ MIZA]; no. PSW 8571 – 4 (1 worker, examined by images) [ UCDC]; Sucre: El Pilar, 10 º 33 'N 63 º09'W, 1.ix. 1986, J.E. Lattke col., no. 1027 (7 workers) [ MIZA]; same data (2 workers) [ MZSP]; Táchira: Las Cuevas, 44 NW S. Cristóbal, 07º 48 'N 71 º 46 'W, 29.xii. 1999, J.E. Lattke col. (1 worker and 1 gyne) [ MIZA]; S. Cristóbal, La Florida, 9.xii. 1985, J.E. Lattke & W.L. Brown cols, no. 727 (5 workers) [ MIZA]; Via Sta. Ana, Río Frío, 14.viii. 1983, J.E. Lattke & G. Borges col. (1 worker) [ MIZA].

FIGURE 12. Worker of Lachnomyrmex pilosus  from Bolívar, Venezuela: A, head in full face view; B, lateral view; C, dorsal view. Image by April Nobile, specimen PSW 8571 - 4.


American Museum of Natural History


Centro de Pesquisas do Cacau


Instituto Nacional de Pesquisas da Amazonia


Museu Paraense Emilio Goeldi


Sao Paulo, Museu de Zoologia da Universidade de Sao Paulo


Smithsonian Institution, National Museum of Natural History


Museo del Instituto de Zoologia Agricola Francisco Fernandez Yepez


R. M. Bohart Museum of Entomology














Lachnomyrmex pilosus Weber, 1950

Feitosa, Rodrigo M. & Brandão, Carlos Roberto F. 2008

Lachnomyrmex pilosus

Lattke 1991: 60
Wheeler 1989: 321
Weber 1950: 1