Strumigenys argiola group

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Strumigenys argiola group Bolton (2000)

Species

Nearctic

Afrotropical-West Palaeartic

Malesian-Oriental-East Palaeartic

Worker Diagnosis

Afrotropical-West Palaeartic

Mandibles in full-face view and at full closure narrow, elongate and curvilinear, emerging far apart on the anterior clypeal margin and with only their extreme apices engaging. Proximal to apices with a wide gap between mandibles, through which the labral lobes are visible. Dorsal surface of mandible basally without a transverse rim or edge that extends across its width in front of the anterior clypeal margin. In profile linear to curvilinear, with an oblique to near-vertical apex and not abruptly narrowed in front of anterior clypeal margin. In ventral view outer margin without an inflected prebasal angle. MI 27-50.

Dentition. Mandible with 0-4 preapical denticles, when present located on distal half of inner margin. Apex of mandible with a near-vertical series of minute teeth or denticles, the apicodorsal and/or apicoventral of which may be slightly to markedly enlarged.

Basal lamella of mandible small, dentiform to low triangular and inconspicuous, very widely separated from basal most tooth; lamella sometimes visible when mandibles fully closed, just in front of anterior clypeal margin, but often concealed by the clypeal margin.

Labrum terminates in a pair of narrow conical lobes that are visible in full-face view when mandibles closed.

Clypeus with anterior margin broad, transverse or medially shallowly convex over the prominent labrum that projects forward between the mandibles. True lateral margin of clypeus extremely short, merging with the preocular carina almost immediately behind the anterolateral clypeal angle.

Clypeal dorsum with small spatulate to large orbicular hairs. Lateral margins of clypeus with a few small anteriorly curved spatulate hairs. Anterior margin with a row of projecting hairs that are short-spatulate or very long and strap-like, or filiform.

Preocular carina visible in full-face view.

Ventrolateral margin of head weakly marginate in front of the small eye, usually shallowly convex and terminating anteriorly at the lowest point of the mandibular insertion.

Postbuccal impression vestigial to absent.

Vertex at or near its highest point evenly curved and convex, without a raised transverse crest.

Cuticle within the antennal scrobe finely sculptured.

Scape very short to short, SI 39-63, dorsoventrally flattened and broad, the leading edge sharp. Subbasal angle broadly rounded and prominent or expanded anteriorly into a large subbasal lobe.

Leading edge of scape with a row of spatulate to spoon-shaped hairs that may be curved toward the apex or the base of the scape.

Pronotum flat to shallowly transversely convex dorsally and bluntly marginate laterally, without a median longitudinal carina. In profile mesonotum flat or forming a convexity or hump behind the pronotum, but usually forming a differentiated surface between pronotum and propodeum.

Propodeum unarmed and the declivity with a lamella extending down each side, or the lamella terminating dorsally in a small triangular tooth.

Legs without trace of femoral or tibial gland bullae.

Spongiform appendages of petiole and postpetiole very variably developed, ranging from massive to absent in the known species. Base of first gastral sternite with or without an arcuate crest of dense spongiform tissue.

Pilosity. Pronotal humeral hair absent. Dorsum of head in full-face view with conspicuous orbicular hairs present (except in Strumigenys anorbicula). Cephalic dorsum and dorsolateral margins without standing or freely projecting hairs (except in anorbicula); apicoscrobal hair always absent. Dorsal alitrunk hairless or pronotum with orbicular hairs similar to those on head; without standing hairs. First gastral tergite with short standing hairs that may be simple, spatulate or clavate. Dorsal (outer) surfaces of middle and hind tibiae with short subapressed to appressed hairs; apicodorsally usually with 1-2 enlarged spatulate hairs.

Sculpture. Dorsum of head behind clypeus and dorsal alitrunk finely reticulate-punctate or shagreenate.

Malesian-Oriental-East Palaeartic

Mandibles in full-face view and at full closure narrow, elongate and curvilinear, emerging far apart on the anterior clypeal margin and with only their extreme apices engaging . Proximal to apices with a wide gap between mandibles, through which the labral lobes are visible. Dorsal surface of mandible basally without a transverse rim or edge that extends across its width in front of the anterior clypeal margin . In profile linear to curvilinear, with an oblique to near-vertical apex and not abruptly narrowed in front of anterior clypeal margin . In ventral view outer margin without an inflected prebasal angle. MI 27 - 50.

Dentition . Mandible with 0 - 4 preapical denticles, when present located on distal half of inner margin. Apex of mandible with a near-vertical series of minute teeth or denticles, the apicodorsal and/or apicoventral of which may be slightly to markedly enlarged.

Basal lamella of mandible small, dentiform to low triangular and inconspicuous, very widely separated from basal most tooth; lamella sometimes visible when mandibles fully closed, just in front of anterior clypeal margin, but often concealed by the clypeal margin.

Labrum terminates in a pair of narrow conical lobes that are visible in full-face view when mandibles closed.

Clypeus with anterior margin broad, transverse or medially shallowly convex over the prominent labrum that projects forward between the mandibles. True lateral margins of clypeus extremely short, merging with the preocular carina almost immediately behind the anterolateral clypeal angles.

Clypeal dorsum with small spatulate to large orbicular hairs. Lateral margins of clypeus with a few small anteriorly curved spatulate hairs. Anterior margin with a row of projecting hairs that are short-spatulate or very long and strap-like.

Preocular carina visible in full-face view.

Ventrolateral margin of head weakly marginate in front of the small eye, usually shallowly convex and terminating anteriorly at the lowest point of the mandibular insertion. Postbuccal impression vestigial to absent.

Vertex at or near its highest point evenly curved and convex, without a raised transverse crest.

Cuticle within the antennal scrobe finely sculptured.

Scape very short to short, SI 45 - 63, dorsoventrally flattened and broad, the leading edge sharp. Subbasal angle broadly rounded and prominent or expanded anteriorly into a large subbasal lobe.

Leading edge of scape with a row of spatulate to spoon-shaped hairs that may be curved toward the apex or the base of the scape.

Pronotum flat to shallowly transversely convex dorsally and bluntly marginate laterally, without a median longitudinal carina. In profile mesonotum flat or forming a convexity or hump behind the pronotum, but usually forming a differentiated surface between pronotum and propodeum.

Propodeum unarmed and the declivity with a lamella running down each side, or the lamella terminating dorsally in a small triangular tooth.

Legs without trace of femoral or tibial gland bullae.

Spongiform appendages of petiole and postpetiole very variably developed, ranging from massive to absent in the known species. Base of first gastral stemite with or without an arcuate crest of dense spongiform tissue.

Pilosity. Pronotal humeral hair absent. Dorsum of head in full-face view with conspicuous orbicular hairs present. Cephalic dorsum and dorsolateral margins without standing or freely projecting hairs; apicoscrobal hair always absent. Dorsal alitrunk hairless or pronotum with orbicular hairs similar to those on head; without standing hairs. First gastral tergite with short standing hairs that may be simple, spatulate or clavate. Dorsal (outer) surfaces of middle and hind tibiae with short subapressed to appressed hairs; apicodorsally usually with 1 - 2 enlarged spatulate hairs.

Sculpture. Dorsum of head behind clypeus and dorsal alitrunk finely reticulate-punctate or shagreenate.

Notes

This group formerly constituted most of the now abandoned genus Epitritus (Bolton, 1999). Its species fall into two complexes, the argiola-complex which occurs in the Palaearctic, Oriental and Afrotropical regions, and the laticeps-complex which is solely Afrotropical. Species with 4-segmented and 6-segmented antennae occur in both complexes.

argiola complex

Members of the argiola-complex have well developed to large spongiform appendages on the waist segments and usually have spongiform tissue also present at the base of the first gastral sternite. They have at least a few pronotal orbicular hairs and usually lack elongate strap-like hairs on the anterior clypeal margin. The first gastral tergite is smooth or at most only very weakly superficially sculptured. In the laticeps-complex spongiform tissue is vestigial or absent on the waist segments and absent from the first gastral sternite. There are no orbicular hairs on the pronotum but the anterior clypeal margin always bears a series of elongate, usually strap-like, hairs. The first gastral tergite is conspicuously sculptured.

To some extent the Afrotropical Strumigenys minima and Oriental Strumigenys lachesis form intermediate grades between the two complexes. In minima the spongiform tissue is not as well developed as in the Palaearctic species but is much better developed than in the other Afrotropical taxa, where reduction to minute vestiges or absence is the rule. In lachesis alone of the argiola-complex are strap-like clypeal hairs present that are similar to those of the laticeps-complex.

laticeps complex

Among species of the laticeps-complex the absence of spongiform tissue on the postpetiole has come about not through its loss but rather by its compaction and sclerotisation so that it secondarily resembles normal cuticle. If the postpetiole is disarticulated from the gaster and viewed from behind the nature of this secondary sclerotisation is immediately apparent (laticeps and roomi dissected).

Malesian-Oriental-East Palaeartic

The five species of the argiola-group found in these regions all fall into the argiola complex. Together they are characterised within the group by the presence of orbicular hairs on the promesonotum as well as on the head, possession of large spongiform appendages on the waist segments and a smooth first gastral tergite. They formed part of the now abandoned genus Epitritus (Bolton, 1999); the Japanese representatives of the group have been treated under this name by Ogata (1991) and Morisita, Kubota et al. (1992). In many characters argiola-group species are convergent upon the Oriental and Malesian species of the Strumigenys murphyi group, two species of which (Strumigenys formosa and Strumigenys murphyi) were originally described in Epitritus.

References

  • Bolton, B. 1999. Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae). Journal of Natural History. 33:1639-1689. PDF
  • Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028.
  • Morisita M., Kubota, M., Onoyama, K., Ogata, K., Terayama, M., Yamauchi, K., Sonobe and R. Yamane. 1992. A guide for the identification of Japanese ants. III. Myrmicinae and supplement to Leptanillinae. (Hymenoptera: Formicidae). Tokyo: Myrmecological Society of Japan. 94 pp.
  • Ogata, K. 1990. A new species of the ant genus Epitritus Emery from Japan (Hymenoptera, Formicidae). Esakia Spec. Issue 1: 197-199 (page 197, figs. 1-3 worker described)