Carebara

Hita Garcia, Wiesel and Fischer (2013) - The taxonomy of the genus has seen great improvements on both generic and regional levels during the last decade (Fernández, 2004, 2006, 2010). The Afrotropical species have yet to be revised and available keys for this species in this region are outdated and fragmentary. The entire genus, with more than 200 species (Bolton, 2012), would benefit highly from an updated revision. Most Carebara are small, cryptic, hypogaeic ants that nest in the soil, the leaf litter or in termite mounds. The latter is important since some species seem to be lestobiotic (Bolton & Belshaw, 1993). Some species (e.g. Carebara castanea) show an extreme size dimorphism between the tiny worker and the very large queen caste.

Identification
Fischer et al. (2015) - Due to a lack of comprehensive revisions and identification keys for Old World Carebara, identifications are challenging. On a regional level, however, taxonomic treatments exist for the Arabian Peninsula (Sharaf and Aldawood 2013), Taiwan (Terayama, Lin and Eguchi 2012), India (Bharti and Kumar 2013), and Fischer et al. (2014) revised the newly defined and mostly Afrotropical Carebara polita group. Weber’s (1950) revision for the Afrotropical Oligomyrmex species is outdated and, as it does not contain a key, is also of very limited use for identifications of the treated species. For the New World, Fernández (2004) published a valuable revision of Carebara with a provisional key, where he synonymized the former genera Oligomyrmex (Mayr), Paedalgus (Forel), and Afroxyidris (Belshaw & Bolton) with Carebara and defined species complexes based on worker morphology. As several previous studies showed (e.g. Ettershank 1966, Fernández 2004, Fischer et al. 2014, and Azorsa and Fisher in revision) all of the synonymized genera were morphologically poorly delimited from Carebara and thus treated as polyphyletic units. Bharti and Kumar (2013) also pointed out the necessity to restructure Fernández’ New World species group definitions in order to incorporate the much more species-rich but poorly studied Old World fauna.

Species Groups

 * Carebara species groups

Distribution
Azorsa and Fisher (2018) - The ant genus Carebara is distributed worldwide, present mainly in tropical and subtropical regions, with approximately 253 described taxa (230 species and 23 subspecies), and the Indomalaya region seems to have more species of Carebara than the other biogeographic regions: 71 species and 14 subspecies (Bolton, 2017).

Biology
Azorsa and Fisher (2018) - Colonies can be large, e.g. colonies of C. overbecki and C. urichi contain up to 1000 individuals (minor and major workers), with the proportion of major workers approaching ten percent (Moffett 1986; Wilson 1962). Minor workers nurse the brood, and major workers defend the nest. The diet of Carebara includes mites, entomobryid collembolans and arthropod eggs (Wilson 1962, 1986), and according to Fischer (2012), six Carebara species from Kenya (Kakamega forest) have specialized predatory diets. Carebara was recorded in almost every habitat in the Malagasy region where an ant collection was made.

Fischer et al. (2015) - The ant genus Carebara is highly diverse with about 250 named taxa to date (Bolton 2014), while the true diversity is probably much higher due to a large number of undescribed species (Fischer et al. 2014). For the vast majority of this diversity virtually nothing is known about their respective ecologies, and data about species’ biogeographic distributions is still incomplete. Apart from the conspicuous, mass-raiding marauder ants of the former genus Pheidologeton (now Carebara, see Fischer et al. 2014), most of the species are minute in size, often with very cryptic lifestyles, making field observation difficult.

Undersampling in many tropical and sub-tropical areas and especially in non-epigaeic strata is still a major issue for Carebara taxonomy and biogeography, and contributes to major gaps in our knowledge. Hence, more ecological and taxonomic studies in these areas are needed in order to better understand the evolution and biology of this interesting and diverse genus.

As in the hyperdiverse genus Pheidole, workers of many Carebara species are divided into two distinct subcastes, minor and major workers (or soldiers), with additonal subcastes and intermediates present in several species (Azorsa and Fisher in revision, Fischer et al. 2014). While the major workers’ most important tasks are chopping and transportation of larger prey and the defence of foraging trails and the nest, the main function of phragmotic workers is blocking nest entrances against intrusion of other predatory ants and invertebrates (Hölldobler and Wilson 1990).

Arabian Peninsula
Sharaf and Aldwood (2013) - Little taxonomic or biological information is available on the genus Carebara throughout its range (Bharti and Kumar 2013), especially in the Arabian Peninsula (Aldawood et al. 2011). The scarcity of information may be due to the cryptic nature of species, tiny body size, and the difficulty in collecting these ants requiring leaf litter sifting and the use of Berlese funnels for extraction. Members of the genus are subterranean and often associated with decaying wood and leaf litter (Bolton 1973, Longino 2004, Aldawood et al. 2011, Bharti and Kumar 2013).

Carebara was originally recorded from the Arabian Peninsula by Collingwood and van Harten (2001) with their description of Oligomyrmex arabicus based on minor and major workers collected from Al Kawd, near Abyan, Republic of Yemen. Ten years later, we described a new species of Carebara, C. abuhurayri Sharaf & Aldawood based on minor workers from the southwestern mountains of Kingdom of Saudi Arabia (KSA) (Aldawood et al. 2011).

Several nest series of a species very similar to C. arabica were collected from four different localities in the southwestern region of KSA. Minor and major workers matched the brief original description of C. arabica. In addition, two major workers of C. abuhurayri were collected from its type locality and are very similar to the major workers of C. arabica. Further comparisons of this newly collected material indicated that C. abuhurayri is a synonym of C. arabicus.

Minor workers of another Carebara species that appeared to be undescribed were collected from Riyadh, KSA. Repeated efforts to find nests of this species that contained all castes were unsuccessful; however, a colony that contained minor and major workers and several alate queens (males unknown) was collected in eastern KSA, confirming the novelty of this taxon.

Castes
Fischer et al. (2014) - Carebara workers may be monomorphic, dimorphic, or continuously polymorphic. When the latter is the case, there are often several subcastes intermediate between minor and large major workers. Intermediate workers of some marauder ant species in the former genus Pheidologeton differ gradually in size and general morphology. In other species with polymorphic workers (e.g. in several former Oligomyrmex) the morphological differences are less gradual, with little variation in the minor workers, but with one to several different major worker phenotypes that differ in size and morphology.

Some species, like Carebara elmenteitae from Kenya, Carebara nayana from India and Carebara butteli from Sri Lanka, however, have an additional major worker subcaste with phragmotic heads, which represent a special defense line against predators and are often described as living plugs for nest entrances.

Azorsa and Fisher (2018) - Carebara characteristically have both very small minor workers and extremely large major workers. The genus contains one of the smallest ants in the world (minor worker of Neotropical Carebara minuta has a head width of 0.21 mm, and total length near 1 mm, while in the Malagasy region the smallest Carebara species is the minor worker of Carebara creolei with a head width of 0.26 mm and a total length near 1.2 mm). The largest major worker in the genus Carebara (major worker of Carebara diversa – formerly Pheidologeton) can reach a total length of 16 mm, while in the Malagasy region the largest Carebara is the major worker of C. jajoby with a total length of 4.53 mm. Workers may be monomorphic, dimorphic or polymorphic. Polymorphism is more noticeable in the major worker caste, with some species having four sizes of major workers (e.g. C. jajoby and C. nosindambo). We did not report any major worker smaller than the minor worker, but this phenomenon may occur in other species of Carebara (Baroni Urbani 1998). The main differences in the morphology of these intermediates include: size differences in the head, posterolateral corners of head, and thorax; larger major workers with one to three ocelli (ocelli are reduced compared to the queen caste); reduced flight sclerites; and eye size differences. It is possible that the intermediates in the major worker caste are trophic specialists like the intermediates of the ant genus Crematogaster (see Peeters et al. 2013).

Fernández 2006 - Longino (2004) calls attention to the paucity of samples of Carebara (lignata group) with both workers and soldiers. In other myrmicine ants like Pheidole or Solenopsis it is not difficult to find workers and soldiers in the field, which suggests that soldiers of Carebara are not present in the same foraging strata as workers. This suggests that, to obtain soldiers of Carebara, we need to dig in the soil or look for them in rotten logs (Longino 2004). The fact that many museums only have minor workers of the typical Carebara (that is, the lignata species group) could be due to the reason pointed out above, and in reality all of the species of this complex may be dimorphic. The exasperating monotony of the minor workers of the lignata species group (some of them only 0.90 mm long!) makes it desirable to obtain and to study collections that include soldiers, besides females and males. If my prediction is correct, and all the species of the lignata group possess major workers (although difficult to collect), it should be possible to revise the group on a global scale.

Finally, I want to call attention to the interesting intercaste phenomenon in this group. Kusnezov (1952) and Wheeler (1925) pointed out and described cases of intermediates between major workers (soldiers) and females. The great plasticity in the external attributes of the soldiers of the lignata species group (such as the presence / absence of ocelli and eyes, and vestigial alary sclerites) make this an ideal group for the study of the evolution of caste intergradations; as proposed by Baroni Urbani and Passera (1996), who suggest that in some cases the soldier developed not from the worker, but from the female (see Ward 1997 for a reply).

Nomenclature

 *  CAREBARA [Myrmicinae: Solenopsidini]
 * Carebara Westwood, 1840b: 86. Type-species: Carebara lignata, by monotypy.
 * Carebara senior synonym of Aeromyrma, Afroxyidris, Aneleus, Crateropsis, Erebomyrma, Hendecatella, Lecanomyrma, Neoblepharidatta, Nimbamyrma, Oligomyrmex, Paedalgus, Solenops, Spelaeomyrmex, Sporocleptes: Fernández, 2004a: 194.
 * Carebara senior synonym of Parvimyrma: Fernández, 2010: 195.
 * Carebara senior synonym of Pheidologeton: Fischer, Azorsa & Fisher, 2014: 63.
 * AEROMYRMA [junior synonym of Carebara]
 * Aeromyrma Forel, 1891b: 198. Type-species: Aeromyrma nosindambo, by monotypy.
 * [Aeromyrma also described as new by Forel, 1891a: cccvii; no species-rank taxa named.]
 * Aeromyrma subgenus of Oligomyrmex: Emery, 1915c: 59 (footnote).
 * Aeromyrma revived status as genus: Arnold, 1916: 256.
 * Aeromyrma subgenus of Oligomyrmex: Emery, 1924d: 215.
 * Aeromyrma junior synonym of Oligomyrmex: Ettershank, 1966: 119.
 * Aeromyrma junior synonym of Carebara: Fernández, 2004a: 194.
 * AFROXYIDRIS [junior synonym of Carebara]
 * Afroxyidris Belshaw & Bolton, 1994: 631. Type-species: Afroxyidris crigensis, by original designation.
 * Afroxyidris junior synonym of Carebara: Fernández, 2004a: 194.
 * ANELEUS [junior synonym of Carebara]
 * Aneleus Emery, 1900c: 327 [as subgenus of Pheidologeton]. Type-species: Solenopsis similis, by subsequent designation of Wheeler, W.M. 1911f: 158.
 * [Type-species not Pheidologeton pygmaeus, unjustified subsequent designation by Wheeler, W.M. 1913a: 77; repeated in Emery, 1924d: 214.]
 * Aneleus raised to genus: Emery, 1914a: 41.
 * Aneleus senior synonym of Sporocleptes: Consani, 1951: 169; Arnold, 1952a: 460.
 * Aneleus junior synonym of Oligomyrmex: Ettershank, 1966: 119.
 * Aneleus junior synonym of Carebara: Fernández, 2004a: 194.
 * CRATEROPSIS [junior synonym of Carebara]
 * Crateropsis Patrizi, 1948: 174 [as subgenus of Solenopsis]. Type-species: Solenopsis (Crateropsis) elmenteitae, by original designation.
 * Crateropsis junior synonym of Oligomyrmex: Ettershank, 1966: 120.
 * Crateropsis junior synonym of Carebara: Fernández, 2004a: 194.
 * EREBOMYRMA [junior synonym of Carebara]
 * Erebomyrma Wheeler, W.M. 1903a: 138. Type-species: Erebomyrma longii, by monotypy.
 * Erebomyrma senior synonym of Spelaeomyrmex: Wilson, 1962a: 63.
 * Erebomyrma junior synonym of Oligomyrmex: Ettershank, 1966: 119.
 * Erebomyrma revived from synonymy: Wilson, 1986b: 61.
 * Erebomyrma returned to synonymy of Oligomyrmex: Bolton, 1994: 106; Bolton, 1995b: 298.
 * Erebomyrma junior synonym of Carebara: Fernández, 2004a: 194.
 * HENDECATELLA [junior synonym of Carebara]
 * Hendecatella Wheeler, W.M. 1927h: 93 [as subgenus of Oligomyrmex]. Type-species: Oligomyrmex (Hendecatella) capreolus, by monotypy.
 * Hendecatella junior synonym of Oligomyrmex: Ettershank, 1966: 119.
 * Hendecatella junior synonym of Carebara: Fernández, 2004a: 194.
 * LECANOMYRMA [junior synonym of Carebara]
 * Lecanomyrma Forel, 1913k: 56 [as subgenus of Pheidologeton]. Type-species: Pheidologeton (Lecanomyrma) butteli, by monotypy.
 * Lecanomyrma subgenus of Aneleus: Emery, 1924d: 215.
 * Lecanomyrma junior synonym of Oligomyrmex: Ettershank, 1966: 119.
 * Lecanomyrma junior synonym of Carebara: Fernández, 2004a: 194.
 * NEOBLEPHARIDATTA [junior synonym of Carebara]
 * Neoblepharidatta Sheela & Narendran, 1997: 88. Type-species: Neoblepharidatta nayana, by original designation.
 * Neoblepharidatta junior synonym of Oligomyrmex: Bolton, 2003: 216, 273.
 * Neoblepharidatta junior synonym of Carebara: Fernández, 2004a: 194.
 * NIMBAMYRMA [junior synonym of Carebara]
 * Nimbamyrma Bernard, 1953b: 240. Type-species: Nimbamyrma villiersi, by monotypy.
 * Nimbamyrma junior synonym of Oligomyrmex: Ettershank, 1966: 120.
 * Nimbamyrma junior synonym of Carebara: Fernández, 2004a: 194.
 * OLIGOMYRMEX [junior synonym of Carebara]
 * Oligomyrmex Mayr, 1867a: 110. Type-species: Oligomyrmex concinnus, by monotypy.
 * Oligomyrmex senior synonym of Aeromyrma, Aneleus (and its junior synonym Sporocleptes), Crateropsis, Hendecatella, Lecanomyrma, Nimbamyrma, Solenops: Ettershank, 1966: 119; Smith, D.R. 1979: 1389.
 * Oligomyrmex senior synonym of Erebomyrma (and its junior synonym Spelaeomyrmex): Bolton, 1994: 106.
 * Oligomyrmex senior synonym of Neoblepharidatta: Bolton, 2003: 216, 273.
 * Oligomyrmex junior synonym of Carebara: Fernández, 2004a: 194.
 * PAEDALGUS [junior synonym of Carebara]
 * Paedalgus Forel, 1911i: 217. Type-species: Paedalgus escherichi, by monotypy.
 * Paedalgus junior synonym of Carebara: Fernández, 2004a: 194.
 * PARVIMYRMA [junior synonym of Carebara]
 * Parvimyrma Eguchi & Bui, 2007: 40. Type-species: Parvimyrma sangi, by original designation.
 * Parvimyrma junior synonym of Carebara: Fernández, 2010: 195.
 * SOLENOPS [junior synonym of Carebara]
 * Solenops Karavaiev, 1930a: 207 [as subgenus of Solenopsis]. Type-species: Solenopsis (Solenops) weyeri, by monotypy.
 * Solenops junior synonym of Oligomyrmex: Ettershank, 1966: 119.
 * Solenops junior synonym of Carebara: Fernández, 2004a: 194.
 * SPELAEOMYRMEX [junior synonym of Carebara]
 * Spelaeomyrmex Wheeler, W.M. 1922c: 9. Type-species: Spelaeomyrmex urichi, by original designation.
 * Spelaeomyrmex junior synonym of Erebomyrma: Wilson, 1962: 63.
 * Spelaeomyrmex junior synonym of Oligomyrmex: Bolton, 1994: 106.
 * Spelaeomyrmex junior synonym of Carebara: Fernández, 2004a: 194.
 * SPOROCLEPTES [junior synonym of Carebara]
 * Sporocleptes Arnold, 1948: 219. Type-species: Sporocleptes nicotianae, by original designation.
 * Sporocleptes junior synonym of Aneleus: Consani, 1951: 169; Arnold, 1952a: 460.
 * Sporocleptes junior synonym of Oligomyrmex: Ettershank, 1966: 119.
 * Sporocleptes junior synonym of Carebara: Fernández, 2004a: 194.
 * PHEIDOLOGETON [junior synonym of Carebara]
 * Pheidologeton Mayr, 1862: 750. Type-species: Oecodoma diversa, by subsequent designation of Bingham, 1903: 160.
 * Pheidologeton senior synonym of Phidologeton: Wheeler, W.M. 1922a: 880.
 * Pheidologeton senior synonym of Amauromyrmex, Idrisella: Ettershank, 1966: 115.
 * Pheidologeton junior synonym of Carebara: Fischer, Azorsa & Fisher, 2014: 63.
 * AMAUROMYRMEX [junior synonym of Carebara]
 * Amauromyrmex Wheeler, W.M. 1929b: 1. Type-species: Amauromyrmex speculifrons (junior synonym of Pheidole silenus), by original designation.
 * Amauromyrmex junior synonym of Pheidologeton: Ettershank, 1966: 115.
 * IDRISELLA [junior synonym of Carebara]
 * Idrisella Santschi, 1937h: 372. Type-species: Pheidologeton dentiviris, by original designation.
 * Idrisella junior synonym of Pheidologeton: Ettershank, 1966: 115.
 * PHIDOLOGETON [junior synonym of Carebara]
 * Phidologeton Bingham, 1903: 160, unjustified emendation of Pheidologeton.
 * Phidologeton junior synonym of Pheidologeton: Wheeler, W.M. 1922a: 880.

Worker
Fischer et al. (2014) (there is also a Malagasy Carebara diagnosis by Azorsa and Fisher, 2018 for the workers that occur in that region. It can be found at the end of the two Malagasy keys - see the list of identication keys above - one for majors and one for minors).

1. Antenna with eight to eleven segments and a two-segmented club.

2. Clypeus of minor workers usually with four distinct setae (some species with a central isolated seta).

3. Mandibles of workers triangular or subtriangular and usually with four to seven teeth or denticles present (3 teeth in Carebara crigensis (Belshaw and Bolton 1994)), the apical and preapical tooth often larger than the following ones.

4. Palp formula 2,2 or 1,2.

5. Frontal lobes separated by median part of clypeus.

6. Eyes either absent or reduced to one or few ommatidia and situated anterior of cephalic midlength, or larger, not reduced, and situated at or posterior of cephalic midlength.

7. Antennal scrobes absent, weakly developed only in species with workers with phragmotic head.

8. Frontal carinae varying from absent to weakly developed and short to very rarely reaching beyond cephalic midlength, but never extending towards posterior head margin.

9. Promesonotal dorsum in profile convex to weakly convex, very rarely near-linear.

10. Propodeum often with a pair of spines, short teeth or angulate posterior corners, in which cases often with a lamella reaching down towards propodeal lobes, but sometimes propodeum posteriorly completely unarmed and rounded.

11. Petiole with a distinct peduncle and well-differentiated node.

12. Different worker subcastes in dimorphic and polymorphic species, sometimes with enormous size variation (e.g. in C. polita group and in many former Pheidologeton).

13. Major workers, where present and especially when large, often with at least a few small remnants of queen flight sclerites present, and some polita group and former Pheidologeton major workers with all flight sclerites recognizable.