Strumigenys arnoldi group

Strumigenys arnoldi group Bolton (2000)

Worker Diagnosis
Apical fork of mandible usually without intercalary teeth (a single species with an intercalary denticle, Strumigenys katapelta). Right mandible with two preapical teeth (a single species with one), the proximal longer than the distal. Left mandible usually with two preapical teeth but some species (dextra-complex) with one. MI 26-77.

Scape rarely subcylindrical, usually weakly to very markedly dorsoventrally flattened. Scape usually relatively short, SI 52-77, but elongate in some species, SI 80-90. Eyes very small or vestigial, maximum eye diameter much less than maximum width of scape.

Upper scrobe margin with a narrow to broad laminate border.

Ventrolateral margin of head without trace of a preocular notch, the margin continuous in front of the eye. Ventral surface of head without a preocular transverse groove but postbuccal groove distinct.

Ventral surface of petiole usually with a conspicuous spongiform strip or curtain, only rarely otherwise; spongiform lobes of postpetiole present but first gastral sternite without a basal spongiform pad.

Pilosity. Pronotal humeral hair absent or present. Apicoscrobal hair absent; upper scrobe margin fringed by a continuous row of small hairs. Cephalic ground-pilosity usually conspicuous and scale-like to spoon-shaped, at least on anterior half of dorsum. Cephalic dorsum with 0-6 standing hairs, usually with a transverse row of 4 near occipital margin and a pair close to highest point of vertex; variously reduced in individual species. Mesonotum usually with a single pair of standing hairs (rarely more). First gastral tergite with simple to remiform hairs; flagellate hairs always absent from gaster.

Sculpture. Head and dorsal alitrunk reticulate-punctate, pronotal dorsum frequently with longitudinal or oblique rugulae or costulae. Pleurae and side of propodeum smooth and gaster unsculptured except for basigastral costulae (except in Strumigenys didyma). Members of the arnoldi-group are best diagnosed by the complete absence of a preocular notch in the ventrolateral margin of the head and consequent lack of a ventral preocular transverse groove that extends across the ventral surface. Coupled with this, the eye is very small, and subappressed to appressed scale-like or spoon-shaped ground-pilosity, at least on the anterior half of the head, occurs in most species of the group.

dextra complex
Strumigenys dextra, Strumigenys irrorata, Strumigenys katapelta, Strumigenys paranax, Strumigenys rakkota

Left mandible with only one preapical tooth (the proximal); right mandible usually with 2 preapical teeth (one species with 1) but the distal small and sometimes concealed by the opposing apicodorsal tooth at full closure. Funicular segments 2 and 3 small but obvious, not fused together nor fused to segment 4, the funiculus distinctly with 5 segments. Combined length of funicular segments 2 and 3 more than half the length of segment 4 (the penultimate segment).

nimbrata complex
Strumigenys bitheria, Strumigenys nimbrata

Left mandible with two preapical teeth. Funicular segments 2 and 3 extremely reduced, partially or entirely fused together and partially fused to segment 4 so that the funiculus appears to have only 3 segments in total, the second of which is minute; combined length of funicular segments 2 and 3 less than half the length of segment 4 (the penultimate segment)

havilandi complex
Strumigenys havilandi, Strumigenys korahyla, Strumigenys semicrypta

Left mandible with two spiniform preapical teeth. Funicular segments 2 and 3 small but obvious, not fused together nor fused to segment 4, the funiculus distinctly with 5 segments. Combined length of funicular segments 2 and 3 more than half the length of segment 4 (the pen ultimate segment). Scapes slender and relatively long, SI 80-90. Head averaging narrower and mandibles longer, CI 67-74; MI 52-77.

arnoldi complex
Strumigenys arnoldi, Strumigenys didyma, Strumigenys mesahyla, Strumigenys omalyx, Strumigenys spathoda, Strumigenys stygia, Strumigenys syntacta, Strumigenys tetraphanes, Strumigenys traegaordhi, Strumigenys ultromalyx

Left mandible with two preapical teeth. Funicular segments 2 and 3 small but obvious, not fused together nor fused to segment 4, the funiculus distinctly with 5 segments. Combined length of funicular segments 2 and 3 more than half the length of segment 4 (the penultimate segment). Scapes moderately to strongly dorsoventrally flattened and short to moderate, SI 52-79. Head averaging broader and mandibles shorter, CI 70-97, MI 34-58.