The Ward ANT Lab

Ants of the subfamily Pseudomyrmecinae


Worker of Pseudomyrmex macrops in Dominican amber (20-30 million years old)
Introduction
Recognition
Outline Of Classification
Phylogenetic Relationships
Keys To Genera
Literature Cited

Identification of Pseudomyrmex Species

Identification of Tetraponera Species  

Introduction

The ant subfamily Pseudomyrmecinae is a pantropical group of arboreal, twig-dwelling ants. A few species occur in warm temperate regions, but most are confined to tropical forests, woodlands, and savannas. Pseudomyrmecine ants typically nest in preformed cavities in dead plant tissue, such as hollow dead twigs or grass culms that have been excavated by other insects. But a substantial number of species (about 20% of the estimated 300 species) are obligate inhabitants of specialized ant-plants. These ants occupy live plant cavities, such as the swollen thorns of certain acacia species or the swollen leaf petioles of leguminous trees of the genus Tachigali, in which they keep their brood and (often) scale insects.

Recognition

 Adult pseudomyrmecine ants present a distinctive appearance (see figures above and below): workers and queens have large conspicuous eyes; the first antennal segment, or scape, is relatively short, less than three-quarters of head length; there is a well developed postpetiole (i.e., a second node-like structure at the "waist"); and a well developed sting. The pronotum and mesonotum of the worker are unfused, and freely articulate with one another.
Pseudomyrmex spinicola worker: frontal view of head (left) and lateral view of body (right).

Other technical characters useful for recognizing the worker and queen castes of these ants include: posteromedial margin of clypeus straight, not extending posteriorly between the frontal carinae; 12 antennal segments (reduced to 11 in two species); median lobes of antennal sclerites visible in a full-face view of the head (i.e., not over-reached by the frontal lobes); opening of metapleural gland located at extreme posteroventral margin of metapleuron; metacoxal cavities closed; and stridulitrum present on the pretergite of abdominal tergite IV. Males can be characterized by their 12-segmented antennae (at least one species is exceptional in having 13 segments), closed metacoxal cavities, well developed postpetiole, and extreme reduction of the volsella. The pseudomyrmecine larva has a trophothylax or "food pocket", a unique structure located on the ventral surface of the thorax, in which the workers place small food particles.

Outline Of Classification

Subfamily Pseudomyrmecinae M. R. Smith, 1952
Type genus: Pseudomyrmex
= Pseudomyrmidae Forel, 1885 (synonymy by Ward, 1990)
= Leptaleinae M. R. Smith, 1951 (synonymy by M. R. Smith, 1952)

Genus Myrcidris Ward, 1990
Type species: Myrcidris epicharis Ward (original designation).
Number of species: 2 (1 undescribed)
Distribution: Brazil, Guyana

Genus Pseudomyrmex Lund, 1831
Type species: Formica gracilis Fabricius (designated by M. R. Smith, 1952)
= Leptalea Erichson, 1839 (synonymy by M. R. Smith, 1952)
= Pseudomyrma Guérin-Meneville, 1844 (synonymy, under Leptalea, by M. R. Smith, 1951)
= Myrmex Guérin-Meneville, 1844 (synonymy, under Pseudomyrma, by . Smith, 1858)
= Ornatinoda Enzmann, 1944 (synonymy by Ward, 1990)
= Clavanoda Enzmann, 1944 (synonymy by Ward, 1990)
= Triangulinoda Enzmann, 1944 (synonymy by Ward, 1990)
= Apedunculata Enzmann, 1944 (synonymy by Ward, 1990)
= Latinoda Enzmann, 1944 (synonymy by Ward, 1990)
Estimated number of species: 200 (approximately 40% undescribed)
Distribution: southern United States to Argentina, Chile

Genus Tetraponera F. Smith, 1852
Type species: Tetraponera atrata F. Smith (= T. nigra (Jerdon)) (designated by Wheeler, 1911)
= Sima Roger, 1863 (synonymy by F. Smith, 1877)
= Pachysima Emery, 1912 (synonymy by Ward, 1990)
= Viticicola Wheeler, 1919 (synonymy by Ward, 1990)
= Parasima Donisthorpe, 1948 (synonymy by Ward, 1990)
Estimated number of species: 100 (approximately 30% undescribed)
Distribution: Africa, Madagascar; India, southeast Asia, Australia

Phylogenetic Relationships

Relationships among the three genera were examined by Ward (1990) who concluded, on the basis of morphological characters, that Myrcidris is the sister group of {Pseudomyrmex + Tetraponera}. A recent, more comprehensive study, based on both morphological and molecular data, demonstrated a sister group relationship between Pseudomyrmex and Myrcidris (Ward & Downie, 2005). DNA sequence data (~5 kb, from five nuclear genes) strongly suggest that Tetraponera is paraphyletic, with one species group (the rufonigra-group) being more closely related to (Pseudomyrmex + Myrcidris) than to other Tetraponera.  This same study also provided evidence that the sister group of Pseudomyrmecinae is the ant subfamily Myrmeciinae (as defined by Ward & Brady, 2003). A summary tree (Ward & Downie, 2005, fig. 2) shows the inferred phylogenetic relationships.

Keys To Genera Of Pseudomyrmecinae (modified from Ward, 1990)

The following measurements (all in mm) and indices are used in the keys below.
HWmaximum width of head, including the eyes
ELeye length: length of the compound eye, measured with the head in full-face (frontal) view
EWeye width: maximum width of the compound eye, measured along the short axis in an oblique dorsolateral view of the head
MD5length of the basal margin of the mandible
MD9length of the masticatory margin of the mandible
OIocular index: EW/EL

Workers and Queens

metabasitarsal sulcus of Myrcidris workermandible with proximal toothmandible lacking proximal tooth
Figure 1Figure 2Figure 3
  1. Antennae 12-segmented; metabasitarsal sulcus variable, always absent in New World species .... 2

    Antennae 11-segmented; metabasitarsal sulcus present (Fig. 1); Brazil, Guyana .... Myrcidris

  2. Mandible nearly always with proximal tooth on basal margin (pbt in Fig. 2); eyes elongate, width two-thirds or less than length (OI 0.50-0.66); metabasitarsal sulcus lacking; southern Nearctic, Neotropical (one species introduced to Hawaii) .... Pseudomyrmex

    Mandible lacking proximal tooth on basal margin (Fig. 3); eyes less elongate, width two-thirds or more than length (OI 0.67-0.95); metabasitarsal sulcus usually present; Paleotropical .... Tetraponera

Males

  1. Antennae 12-segmented; posterior margin of sternum VIII emarginate; external face of aedeagus lacking cornuti .... 2

    Antennae 13-segmented; posterior margin of sternum VIII broadly convex; external face of aedeagus with cornuti; Brazil, Guyana .... Myrcidris

  2. Masticatory margin of mandible with 6-18 teeth or denticles (or very rarely edentate), those preceding the apical tooth often quite small and abraded; if only 6 teeth present, then species small in size (HW < 0.98); basal margin of mandible one half or less the length of the masticatory margin (MD5/MD9 < 0.56), the two converging angularly at the apicobasal tooth or corner; New World .... Pseudomyrmex

    Masticatory margin of mandible usually with 2-5 teeth, typically subequal in size; rarely with 6 teeth, in which case HW > .99; basal margin of mandible two-thirds or more the length of the masticatory margin (MD5/MD9 < 0.64), the juncture between the two angular or rounded; Old World .... Tetraponera

Literature Cited