Cheliomyrmex Mayr, 1870

Borowiec, Marek L., 2016, Generic revision of the ant subfamily Dorylinae (Hymenoptera, Formicidae), ZooKeys 608, pp. 1-280 : 86-90

Taxon classification Animalia Hymenoptera Formicidae

Cheliomyrmex Mayr, 1870

Type-species.

Cheliomyrmex nortoni (junior synonym of Labidus morosus ), by monotypy.

Cheliomyrmex is a rarely encountered genus of New World army ants that is a mostly subterranean predator with likely a specialized diet.

Diagnosis.

Worker. Workers of Cheliomyrmex can be recognized by a combination of propodeal spiracle positioned high on the propodeum, propodeal declivity simple and not armed with cuticular ridges or denticles, abdominal segment III small but broad posteriorly and thus waist appearing one-segmented, pygidium small and armed with at most a pair of modified setae, and pretarsal claws armed with a tooth. Cheliomyrmex is perhaps most similar to Labidus and certain Neivamyrmex but it is unique among New World army ants in having abdominal segment III broadly attached to segment IV (i.e. it has a uninodal waist) and thus easily told apart from all other army ant genera in this region.

Male. The males of Cheliomyrmex share the following wing venation characters with other New World army ants ( Eciton , Labidus , Neivamyrmex and Nomamyrmex ): costal (C) vein present in the fore wing, relatively narrow pterostigma, presence of vein 2 rs-m and two closed submarginal cells, marginal cell closed by R·f3 and Rs·f4-5, 2rs-m present, and M·f1 vein arising from M+Cu at an angle lower than 45° and conspicuously proximal to cu-a. This characteristic venation pattern serves to distinguish New World army ants from the Old World army ants ( Aenictogiton , Aenictus , Dorylus ) that have no vein R·f3 and where M·f1 arises near cu-a and at an angle close to or higher than 45°. Aenictus and Dorylus additionally have no vein Rs·f2-3 and so only one submarginal cell that is closed distally by 2rs-m. In other dorylines with well-developed wing venation (e.g. Chrysapace , Cylindromyrmex ) the vein M·f1 arises distal to cu-a and pterostigma is very broad and conspicuous. Within the New World army ants, wing venation is relatively conserved and thus of little use in discrimination of genera. Genitalic characters have been found to be the most reliable ( Watkins 1976), although impossible to ascertain without dissection. A combination of absence of very long setae approaching femur length on the abdomen, apices of penisvalvae with setae, and the sternite of abdominal segment IX (subgenital plate) with four teeth, and a simple hind basitarsus will distinguish Cheliomyrmex males from all other army ant genera in the New World. The long setae on gaster are characteristic of Nomamyrmex . The penisvalvae with setae are also present in Labidus but the latter can be told apart by having only two teeth on the abdominal sternite IX and a complex hind basal tarsal segment, which has a conspicuous oblique groove that accommodates the hind tibial spur.

Description.

Worker.Head: Antennae with 12 segments. Apical antennal segment not enlarged, not broader and longer than two preceding segments combined. Clypeus without cuticular apron. Lateroclypeal teeth absent. Parafrontal ridges reduced. Torulo-posttorular complex vertical. Antennal scrobes absent. Labrum with median notch or concavity. Proximal face of stipes not projecting beyond inner margin of sclerite, prementum exposed when mouthparts fully closed. Maxillary palps 2-segmented. Labial palps 3-segmented. Mandibles polymorphic, from triangular with teeth through triangular with median tooth to falcate, with teeth on elongated masticatory margin. Eyes present, composed of 1-5 ommatidia. Ocelli absent. Head capsule with differentiated vertical posterior surface above occipital foramen. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Posterior head corners dorsolaterally immarginate. Carina surrounding occipital foramen ventrally absent. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Promesonotal connection with Pronotomesopleural suture completely fused. Pronotomesopleural suture visible, unfused partway to notal surface. Mesometapleural groove weakly impressed. Transverse groove dividing mesopleuron present. Pleural endophragmal pit concavity present. Mesosoma dorsolaterally immarginate. Metanotal depression or groove on mesosoma present. Propodeal spiracle situated high on sclerite. Propodeal declivity without distinct dorsal edge or margin and rectangular in posterior view. Metapleural gland with bulla visible through cuticle. Propodeal lobes absent. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle marginate. Helcium in relation to tergosternal Pronotomesopleural suture placed at Pronotomesopleural suture and infraaxial. Prora narrowed into anteriorly directed spine. Spiracle openings of abdominal segments IV–VI oval. Abdominal segment III anterodorsally immarginate and dorsolaterally immarginate. Abdominal segment III more than half size of succeeding segment IV, which is weakly constricted at presegmental portion (uninodal waist). Girdling constriction of segment IV present, i.e. pre- and postsclerites distinct. Cinctus of abdominal segment IV gutter-like, not sculptured. Abdominal segment IV not conspicuously largest segment. Abdominal tergite IV not folding over sternite, and anterior portions of sternite and tergite equally well visible in lateral view. Girdling constriction between pre- and posttergites of abdominal segments V and VI absent. Girdling constriction between pre- and poststernites of abdominal segments V and VI absent. Pygidium small, reduced to narrow strip, without impressed medial field, and simple, not armed with cuticular spines or modified setae. Hypopygium unarmed. Legs: Mid tibia with single pectinate spur. Hind tibia with single pectinate spur. Hind basitarsus not widening distally, circular in cross-section. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland present as oval patch of whitish cuticle. Metabasitarsal gland absent. Hind pretarsal claws each armed with a tooth. Polymorphism: Polymorphic.

Male.Head: Antennae with 13 segments. Clypeus without cuticular apron. Parafrontal ridges absent. Torulo-posttorular complex vertical. Maxillary palps 2-segmented. Labial palps 3-segmented. Mandibles falcate. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Carina surrounding occipital foramen ventrally absent. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Notauli absent. Transverse groove dividing mesopleuron absent. Propodeal declivity reduced, without distinct dorsal edge or margin. Metapleural gland opening absent. Propodeal lobes absent. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle immarginate. Helcium in relation to tergosternal Pronotomesopleural suture placed at Pronotomesopleural suture and axial. Prora simple, not delimited by carina. Spiracle openings of abdominal segments IV–VI slit-shaped. Abdominal segment III more than half size of succeeding segment IV; latter weakly constricted at presegmental portion (uninodal waist). Girdling constriction of segment IV absent, i.e. pre- and postsclerites indistinct. Cinctus of abdominal segment IV absent, not impressed. Girdling constriction between pre- and postsclerites of abdominal segments V and VI absent. Abdominal segment IV not conspicuously largest segment. Abdominal sternite VII simple. Abdominal sternite IX distally armed with two outer spines and additional two inner denticles, with lateral apodemes longer than much reduced medial apodeme, directed anteriorly (towards head). Genitalia: Cupula very long, nearing or surpassing length of rest of genital capsule and shorter ventrally than dorsally. Basimere narrowly fused to telomere, with sulcus visible at least partway through junction, and ventrally with left and right arms abutting. Telomere expanded at apex. Volsella narrow, hook-shaped. Penisvalva not flattened at apex, expanded. Legs: Mid tibia with single pectinate spur. Hind tibia with single pectinate spur. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland absent. Metabasitarsal glands absent. Hind pretarsal claws each armed with a tooth. Wings: Tegula present, broad, demiovate in shape. Vein C in fore wing present. Pterostigma narrow. Abscissa R·f3 present, running toward dis tal wing margin and enclosing cell with Rs·f5. Abscissae Rs·f2-3 present, connecting with Rs+M&M·f2. Cross-vein 2r-rs present, differentiated from Rs·f4 by presence of Rs·f2-3. Abscissae Rs·f4-5 differentiated into Rs·f4 and Rs·f5 by 2rs-m. Abscissa M·f2 in fore wing present, separated from Rs+M by Rs·f2. Abscissa M·f4 in fore wing present, reaching wing margin. Cross-vein 1m-cu in fore wing present. Cross-vein cu-a in fore wing present, arising from Cu and distal to, at or near M·f1. Vein Cu in fore wing present, with both branches Cu1 and Cu2. Vein A in fore wing with abscissae A·f1 and A·f2 present. Vein C in hind wing present. Vein R in hind wing present, extending past Sc+R but not reaching distal wing margin. Vein Sc+R in hind wing present. Abscissa Rs·f1 in hind wing present, shorter than 1rs-m. Abscissa Rs·f2 in hind wing present, reaching wing margin. Cross-vein 1rs-m in hind wing present, about as long as M·f1. Vein M+Cu in hind wing present. Abscissa M·f1 in hind wing present. Abscissa M·f2 in hind wing present. Cross-vein cu-a in hind wing present. Vein Cu in hind wing present. Vein A in hind wing with abscissae A·f1 and A·f2 present.

Gyne. Not described.

Larva. Larvae of Cheliomyrmex megalonyx have been described ( Wheeler 1943, Wheeler and Wheeler 1984). Presence of cocoons unknown.

Distribution.

Cheliomyrmex is present in most of Central America, including southern Mexico, Belize, Guatemala, Honduras, and Panama, but so far it has not been collected in Nicaragua or Costa Rica. It is also known from northern and northwestern South America south to Peru and Bolivia.

Taxonomy and phylogeny.

Cheliomyrmex was introduced by Mayr in 1870 who described Cheliomyrmex nortoni , now a junior synonym of Cheliomyrmex morosus ( Smith 1859) and recognized its affinity to other dorylines. The genus-level taxonomy of Cheliomyrmex has been relatively stable and there are four currently recognized species. Because of its morphology, notably the fact that Cheliomyrmex are the only New World army ants that possess only a single waist segment, the genus has been often considered of particular importance to army ant systematics ( Wheeler 1921, Gotwald 1971, Gotwald and Kupiec 1975, Gotwald 1979). However, the current understanding of doryline phylogeny shows Cheliomyrmex nested within the New World army ants ( Brady et al. 2014), sister to the ( Labidus ( Eciton plus Nomamyrmex )) clade.

Biology.

Ants in this lineage have been rarely observed or collected. The raids and emigrations of these ants are mostly subterranean, only occasionally seen above ground. Raids have been observed mostly under stones or rotting wood ( Wheeler 1921, Gotwald 1971). A diverse fauna of associates was reported from an emigration column of Cheliomyrmex morosus , including phorid flies, staphylinid beetles, silverfish and mites ( Berghoff and Franks 2007). The 2007 study and the only other published observation of a Cheliomyrmex emigration ( Cheliomyrmex megalonyx ; Wheeler 1921), described galleries of soil built by the ants to cover the areas where the ant columns had to proceed on the surface. Wheeler also reported a behavior where stationary major workers were guarding the emigration columns and compared it to that of African Dorylus , although this behavior is also known in Labidus ( Rettenmeyer 1963). As Wheeler observed only larvae being carried by the workers, it has been postulated that brood production is synchronized ( Rettenmeyer 1963). Cheliomyrmex andicola has been observed feeding on a dead snake and actively pursuing and killing a giant earthworm in Ecuador ( O’Donnell et al. 2005). Given that no other prey has been observed for this genus, combined with the specialized mandibular morphology and potent sting, O’Donnell et al. (2005) proposed that Cheliomyrmex are specialized predators of large subterranean invertebrates or maybe even vertebrates.

Species of Cheliomyrmex

Cheliomyrmex andicola Emery, 1894: Peru

Cheliomyrmex audax Santschi, 1921b: Ecuador

Cheliomyrmex megalonyx Wheeler, W. M., 1921: Guyana

Cheliomyrmex morosus (Smith, 1859): Mexico