Hylomyrma

Ulyssea & Brandao (2021) report that our knowledge about the biology of this genus is restricted to a few label data and rare observations of live specimens. Hylomyrma species are commonly collected in leaf-litter samples of wet and dry environments submitted to winkler extractors, indicating, therefore, a preference for forested habitats or cropping areas with soil covered with litter.

One colony of Hylomyrma blandiens was collected by M.A. Ulysséa inside a fallen twig (10 cm length x 4 cm diameter) found among the leaf-litter in Madre de Dios, Peru. The colony had 24 specimens, comprising three queens (two callow with wings) and 21 workers, as well as plant remains and parts of a Curculionidae imago. There was no brood (larvae or pupae) inside this nest. Wilson observed that, in captivity, Hylomyrma versuta workers captured Drosophila spp., Isotoma viridis Bourlet, 1839 (springtails), and other selected small invertebrates offered in the feeding chamber, which they used to feed the larvae (Wheeler & Wheeler 1960). The colonies are apparently rather small; most of the leaf-litter samples included only one to three individuals of Hylomyrma. Exceptionally, five to fifteen specimens of Hylomyrma villemantae and nine Hylomyrma reitteri were collected in a few samples. Samples with five, seven or at most ten specimens are rare. When disturbed, the workers tend to assume a dead posture (thanatosis), which makes their visualization in field conditions very challenging (personal observation to Hylomyrma immanis and H. reitteri), because in thanatosis they resemble small litter debris.

Identification
Relatively small ants (TL 4.15–6.6 mm, WL 1.08–1.75 mm); palpal formula 4:3; antennal club 4-segmented; anterior margin of clypeus bidentate; dorsal margin of mesosoma predominantly convex; prominent projections on the region of confluence between ventral and posterolateral margins of pronotum, and on the anteroventral margin of mesepisternum; propodeal spiracle aligned with the base of propodeal spine; propodeal spine well-developed; propodeal lobe uni- or bidentate; meso- and metatibial spurs sharp, with interior margin serrated; petiole relatively elongated and narrow. (Ulyssea & Brandao, 2021)

Hylomyrma can be easily differentiated from the other two Pogonomyrmecini genera. Pogonomyrmex species have the anterior margin of clypeus unarmed whereas Hylomyrma presents a pair of lateral teeth. Patagonomyrmex has a somewhat straight dorsal margin of mesosoma, and the petiolar node is strongly subtriangular, while in Hylomyrma the dorsal margin of mesosoma is predominantly convex and the dorsal margin of the petiole can be continuous and convex, or discontinuous, with the anterior surface of node differentiated from anterior peduncle in lateral view. (Ulyssea & Brandao, 2021)

Biology
Pierce et al. (2017) - Little is known about the biology and natural history of Hylomyrma. The genus is restricted to wet forests, mostly lowland rainforest, where it is a member of the cryptic leaf litter ant community. It is known almost exclusively from Winkler and Berlese samples (J.T. Longino, unpubl.), and observations of nesting or foraging habits are extremely limited. A colony was discovered by E.O. Wilson in Veracruz, Mexico, and kept in an artificial nest for observation. He observed that "In captivity workers of this species captured Drosophila spp., Isotoma viridis Bourlet [Collembola], and a few other small insects offered them in the food chamber, and fed them directly to the larvae" (quoted in Wheeler & Wheeler 1960: p. 4). As far as we know, this is still the only published reference to a colony of Hylomyrma. At the time of the 1973 revision, Kempf had perhaps fewer than 100 specimens to examine. Since that time, mass collecting techniques and large faunal surveys, mainly in Central America, have yielded thousands of specimens from many localities.

Nomenclature

 *  HYLOMYRMA [Myrmicinae: Myrmicini]
 * Hylomyrma Forel, 1912g: 16 [as subgenus of Pogonomyrmex]. Type-species: Pogonomyrmex (Hylomyrma) columbicus, by original designation.
 * Hylomyrma raised to genus: Wheeler, W.M. 1922a: 660 (in key).
 * Hylomyrma senior synonym of Lundella: Brown, 1953h: 3.
 * LUNDELLA [junior synonym of Hylomyrma]
 * Lundella Emery, 1915i: 191. Type-species: Tetramorium reitteri, by original designation.
 * Lundella junior synonym of Hylomyrma: Brown, 1953h: 3.

Pierce et al. (2017) - Hylomyrma is an exclusively Neotropical ant genus that occurs from southern Mexico to Argentina. Originally described as a subgenus within Pogonomyrmex it was elevated to generic status by Wheeler (1922). Hylomyrma has always been considered a close relative of Pogonomyrmex, and this was convincingly demonstrated in recent molecular studies (Brady & al. 2006, Ward & al. 2015, Branstetter & al. 2017). The only thorough species-level revision was by Kempf (1973), in which twelve species were recognized. The genus has received little attention since Kempf's revision, with only one additional species being described (Kutter 1977). Despite there being few studies, there is little doubt of the monophyly of Hylomyrma.