Typhlomyrmex

A small primarily neotropical genus. Workers are small, have reduced eyes and are rarely sampled. It appears all the species nest and forage within soil or rotting wood. Being a cryptic, both in its taxonomy and ecology, it seems to compare with that of other subterranean ant genera such as Leptanilloides, which has many species still waiting to be described and a largely unknown ecology (Delsinne et al. 2015; Lacau et al. 2008; Fernández et al. 2023).

Identification
Lacau, Villemant & Delabie (2004) - The genus is morphologically homogenous, but there is interspecific variation in petiole shape, head shape, and body size (Brown, 1965; Lacau et al., unpublished data). The terricolous species are the smallest. Bolton (2003: 46) proposed the following potential autapomorphies for the genus: “workers eyes vestigial to absent,” and “male hypopygium with an elongate upcurved and median digitiform process.” The first character has been reported as homoplasic for the entire family by Baroni Urbani et al. (1992): the eye reduction occurs in many other ant genera with hypogaeic habits, in several subfamilies (Hölldobler & Wilson, 1990).

All Typhlomyrmex species share a cryptic ecology and reduced eyes, but it is unknown if this character represents an autapomorphy for the genus in the clade Ectatomminae and/or a convergent adaptation between different Typhlomyrmex species. The digitiform process on the male hypopygium, proposed as autapomorphic by Bolton, is uniformly present in Typhlomyrmex but also occurs in some Gnamptogenys. The digitiform process is possibly homologous in the two taxa (Lacau, unpub.) and should be considered homoplasic. Thus, no clear autapomorphy distinguishes Typhlomyrmex from other ectatommine genera and its position in this subfamily remains unclear.

Species by Region
Number of species within biogeographic regions, along with the total number of species for each region.

Biology
Lacau, Villemant & Delabie (2004) - Compared to other poneromorph genera (sensu Bolton, 2003), Typhlomyrmex biology remains largely unknown but the rare available data reveal a strong ecological diversity between species. Although the distributions of individual species are highly variable, the genus has one of the largest distributions among the New World endemic poneromorph genera (Kempf, 1972). For example, the type species, Typhlomyrmex rogenhoferi which was described from Amazonas State (Brazil), is spread from northern Argentina to southern Mexico (Kempf, 1972; Longino, 1999; Lattke, 2003; Lacau et al., in progress). In contrast, others species have a much more reduced distribution and several are known only from a single locality. Typhlomyrmex meire is only found in a narrow part of the cocoa producing region of southern Bahia (Brazil). Typhlomyrmex prolatus and Typhlomyrmex foreli are two other endemic species respectively described from San Jose (Costa Rica) and Rio Negro (Brazil, Paraná State) regions (Brown, 1965). These restricted geographic ranges must be considered with circumspection owing to the scarcity and the disparity of the data concerning the diversity and the distribution of the Neotropical Formicidae (Kempf, 1972). In fact, ants remain undersampled in large areas of South and Central America. Many species currently regarded as rare or endemic could be relatively common in poorly known regions. This is particularly true for Typhlomyrmex species because they are all cryptobiotic, nesting and foraging within soil or rotting wood. The autoecology of Typhlomyrmex species appears as variable as their distribution. Typhlomyrmex rogenhoferi is an epigaeic species that colonizes large dead trunks lying on the rain forest floor (Lacau et al., 2001), while the others species are subterranean and terricolous. In particular, the small colonies of Typhlomyrmex pusillus nest in minute soil chambers (Brown, 1965; Lacau, pers. obs.); its biological cycle remains almost completely subterranean and only the winged gynes and males periodically emerge for mating.

The genus Typhlomyrmex is generally considered to be rare (Brown, 1965) because these ants are very difficult to find in the field. The terricolous species are rarely collected with extraction traps such as Winkler or Berlese-Tullgren collectors because workers only occasionally forage in the litter (Ward, 2000; Lacau, pers. obs.). Also they are not found in woody macro-elements of litter, such as little branches or dried fruits, nor in logs (see Carvalho & Vasconcelos, 2002; Delabie et al. 1997; Lacau, pers. obs.). The best technique to find living colonies is to look for individuals by careful hand fragmentation of soil elements.

Such laborious field collecting explains the scarcity of Typhlomyrmex specimens in museum collections, especially when compared with those of other poneromorph genera such as Pachycondyla and Hypoponera. Furthermore, the morphology of the different castes is rarely known. For example, Typhlomyrmex prolatus and Typhlomyrmex foreli are only known from their winged queen holotype. In the other taxa, the castes were frequently described separately, from material collected in different localities so that complete series including workers, queens and males coming from the same colony or even from a single location are extremely rare in collections.

Fernández et al. (2023) - Soil and subterranean ants tend to be under-studied and under-sampled, and thus less represented in biological inventories compared to other ants (Wong and Guénard 2021). Typhlomyrmex is a cryptic genus both in its taxonomy and its ecology (Lacau et al. 2008); Its current state seems to compare with that of other subterranean ant genera such as Leptanilloides, which has many species still waiting to be described and a largely unknown ecology (Delsinne et al. 2015).

Most of the records reported in this work were collected in soil macrofauna sampling protocols, using the Tropical Soil Biology and Fertility (TSBF) monolith method (Anderson and Ingram 1993, ISO 2011). With the TSBF monolith method, Typhlomyrmex clavicornis and Typhlomyrmex prolatus were found even at a depth of 30 cm. Additionally, other species of Typhlomyrmex are also abundant at these depths, including Typhlomyrmex pusillus (Castro et al. 2018b, Castro et al. 2023). This method, which focuses on soil fauna, seems to be useful for collecting cryptic organisms that are usually under-sampled with other methods such as Winkler sacs and Berlese traps (Castro et al. 2018a).

Based on our results, it can be inferred that Typhlomyrmex is a genus affected by the Wallacean shortfall (Bini et al. 2006; Meurgey and Ramage 2020). This premise had already been addressed by Lacau et al. (2004, 2008), where they state that Typhlomyrmex species, such as T. pusillus and Typhlomyrmex rogenhoferi, are the most recorded species in the literature, likely due to their wide distribution that ranges from the southern South America to southern North America (Longino et al. 2002; Fernández and Sendoya 2004; Vittar 2008; Basset et al. 2012; Dáttilo et al. 2020; Camacho et al. 2022). Meanwhile, the greater diversity within this genus is largely unknown. Therefore, the presence of T. prolatus in South America further indicates that the information for the other Typhlomyrmex species is still very limited, and although the species richness may be higher than currently known, so too is the distribution of less abundant or taxonomically more cryptic Typhlomyrmex species. Another case of the Wallace shortfall in Typhlomyrmex is observed in T. clavicornis, although this species has records in five South American countries, including Brazil but only in the state of Rio de Janeiro in the southeast. The lack of records in the Brazilian Amazon basin and Cerrado, where it would be presumed to be present by the other valid records in countries with those biomes present; this study is intended to facilitate the identification of these widely distributed species and would help to reduce this biogeographical gap.

Although we described Typhlomyrmex encanto, this species may have been reported in the literature as Typhlomyrmex sp. A (Lacau et al. 2008), however those specimens were not available for study. Given the difficulty in accessibility to the specimens described by Lacau et al. (2008), here we describe specimens from recent collections from Colombia. In their treatment of the Typhlomyrmex from Colombia, Lacau et al. (2008) mention another unnamed species, Typhlomyrmex sp. B, which could potentially also be a new species. In the key provided by Lacau et. al. (2008), they characterized T. sp. B with the following, translated from French: “Head capsule whose maximum width is located at two-thirds of its length, with weakly converging side faces anteriorly; occipital carina visible laterally; clypeus in dorsal view forming a wide, very flared convexity; clypeal lamella bearing a large well-advanced, convex median lobe but clearly truncated at the apex; scape in dorsal view, greatly enlarged towards the back in its distal half; wide and superficial metanotal furrow, little marked but distinct”. The authors refer to 6 workers with vouchers (SL#184, SL#185, SL#186, SL#529, SL#531 and SL#568) and labeled COLOMBIA, Caquetá PNN, Los Picachos, 1775m, 02°48'N, 74°40'W, Manual 3, 3. xi. 1997, F. Escobar, leg. in the IAvH collection. However, in a recent visit to the IAvH collection it was impossible to locate these workers with these voucher specimens, or any other material that could be associated with Typhlomyrmex sp. B. As is the case of Typhlomyrmex sp. A, the Typhlomyrmex sp. B description has not been published nor are there any plans to do so (Jacques Delabie, pers. comm.). Taxonomic work on cryptic groups such as this one is necessary to increase the knowledge of ant groups that, although currently under-studied and poorly understood, may be abundant and widely distributed.

Castes
Lacau et al. 2008 reported the existence of both winged and ergatoid queens in one species ("sp. 4").

Nomenclature

 *  TYPHLOMYRMEX [Ectatomminae: Typhlomyrmecini]
 * Typhlomyrmex Mayr, 1862: 736. Type-species: Typhlomyrmex rogenhoferi, by monotypy.
 * [Typhlomyrmex Gistel, 1856: 447. Nomen nudum; see Wheeler, W.M. 1911c: 858.]