Strumigenys chapmani group

Strumigenys chapmani group Bolton (2000)

Species

Malesian-Oriental-East Palaeartic

Worker Diagnosis

Apical fork of mandible with 3 spiniform teeth; 1-2 intercalary denticles present that arise from the dorsal surface of the apicoventral tooth. Apical series of teeth not vertical but rather the apicoventral tooth (and often also the apicomedian tooth) rolled under and encroaching upon the ventral surface of the mandible; in extreme cases the apicoventral tooth, in full-face view, appears as a preapical tooth that arises from the ventral surface of the mandible. Normally-arising preapical teeth or denticles absent. MI 34-57.

Anterior clypeal margin transverse or very slightly concave medially.

Head in full-face view broad to very broad, CI 84-102; in profile head capsule distinctly dorsoventrally flattened.

Scape short and stout, strongly dorsoventrally flattened. SI 43-54.

Apical antennomere not constricted basally.

Ventrolateral margin of head with or without a preocular notch; with head in profile the ventral outline with a broad concavity behind the level of the eye.

Scrobe in profile deeply impressed and with dorsal margin sharply defined.

Propodeal teeth free; margin of declivity with a carina or narrow cuticular flange, never with a broad lamella.

Spongiform appendages of waist segments all present; lateral lobe of petiole small and posterior in profile.

Pilosity. Pronotal humeral hair either absent or not strongly differentiated from the remainder of the pronotal pilosity. Apicoscrobal hair absent or with a short stout hair in this position. First gastral tergite may have remiform or flagellate hairs but the latter never occur on head or alitrunk. Ground-pilosity of head subappressed to appressed and dense, of short broad spatulate or spoon-shaped hairs. Hind tibia and/or basitarsus with long suberect to erect hairs. Hairs on leading edge of scape coarse and flattened apically, suberect to almost erect.

Sculpture. Either the usual reticulate-punctate sculpture on head and alitrunk or with parts reduced from this. Disc of postpetiole usually smooth, rarely sculptured. Gaster unsculptured except for basigastral costulae, which may be short.

Notes

The apicodorsal tooth of the tridentate mandibular fork appears to have its origin in a preapical tooth that has shifted to the apex and increased markedly in size. Judging from the position of the intercalary denticles the middle and lower teeth represent the original bidentate fork, now somewhat reduced in size and rolled under the new apicodorsal tooth. Species of the akalles group have what appears to be a similarly constructed mandibular apex, but the original apical fork is not rolled under and each mandible also retains a large preapical tooth (see there). The only other group exhibiting a tridentate fork is that of Strumigenys trixodens, but here the third tooth appears to have arisen by elongation of what was originally a median intercalary tooth between the apicodorsal and apicoventral teeth of an originally bidentate apical fork.

References

Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028.