Strumigenys rostrata group

Strumigenys rostrata group Bolton (2000)

Neartic

 * Strumigenys arizonica
 * Strumigenys bunki
 * Strumigenys californica
 * Strumigenys carolinensis
 * Strumigenys chiricahua
 * Strumigenys hyalina
 * Strumigenys inopina
 * Strumigenys rostrata

Malagasy

 * Strumigenys ambatrix
 * Strumigenys fautrix
 * Strumigenys symmetrix
 * Strumigenys victrix

Worker Diagnosis
The group is diagnosed, with slight differences, for three different regions:

Neartic
Mandibles in full-face view and at full closure triangular, either serially dentate with masticatory margins that engage through all their visible length or with an edentate gap present between basal tooth and anterior clypeal margin. In ventral view outer margin of mandible without an inflected prebasal angle. MI 15-25.

Dentition. Principal tooth row with 5 sharp triangular teeth. Tooth 1 (basal) and 2 subequal in size or one longer than the other, tooth 3 distinctly longer (longest tooth on margin) and 4 reduced, smaller than 3 or 5. Tooth 5 usually only slightly shorter than 3 and hence usually the second longest tooth on the margin. Tooth 5 followed by two small teeth, 4 minute denticles and a small apical tooth, giving a total dental count of 12.

Basal lamella of mandible triangular, broad-based and longer than the longest tooth, not visible to partially visible in full-face view with the mandibles fully closed. Basal lamella not separated from basal tooth or with a small to obvious diastema present (see note, below).

Labrum terminates in a pair of narrow digitate to conical lobes.

Clypeus with anterior margin broad, shallowly convex , transverse or shallowly concave in full-face view. Lateral clypeal margins approximately straight to convex, and weakly to distinctly convergent anteriorly. In ventral view the lateral clypeal margins extend well beyond the outer margins of the fully closed mandibles.

Clypeus without peripheral groove.

Clypeal lateral margins with a continuous fringe of anteriorly curved broadly spatulate to spoon-shaped hairs. Anterior margin with smaller hairs that are directed anteriorly or curved toward the midline. Clypeal dorsum with small spatulate or spoon-shaped hairs, without any other form of pilosity.

Preocular carina broad and conspicuous in full-face view.

Ventrolateral margin of head between eye and mandible bluntly to quite sharply marginate.

Postbuccal impression small and shallow to vestigial.

Cuticle of side of head within scrobe reticulate or reticulate-punctate.

Scape short to moderate, SI 67-82, weakly to moderately dorsoventrally flattened, the dorsum and ventre converging anteriorly so that the leading edge is sharp or even a thin flange or lamella. Ventral surface of scape behind the leading edge usually weakly concave.

Leading edge of scape with conspicuously spatulate to spoon-shaped hairs, some of which are curved toward the base of the scape.

Propodeum with triangular teeth subtended by a lamella on each side that is sometimes broad and engages the teeth through most of their length.

Spongiform appendages well developed on petiole and postpetiole; ventral spongiform curtain of petiole well developed. Base of first gastral sternite in profile with a narrow band or thin pad of weak or diffuse spongiform tissue that frequently appears hair-like.

Pilosity. Pronotal humeral hair usually present, elongate and straight or flagellate. Dorsum of head behind clypeus with spatulate to spoon-shaped ground-pilosity. Dorsolateral margin of head with or without an apicoscrobal hair. First gastral tergite usually with simple pilosity present, more rarely with flagellate hairs.

Sculpture. Dorsum of head behind clypeus reticulate-punctate. Pleurae, side of propodeum and disc of postpetiole smooth.

Malagasy
Mandibles in full-face view and at full closure triangular to elongate-triangular, with serially dentate masticatory margins that engage through all or most of their visible length; a small gap usually visible between basal tooth and anterior clypeal margin. In ventral view outer margin of mandible without an inflected prebasal angle. MI 16-20.

Dentition. Basal dental row of 7 short triangular teeth,either all about the same size or with alternating very slightly taller and very slightly shorter teeth. Basal lamella not separated from basal tooth or with a very short diastema present. Distalmost 2 teeth of the basal row small, followed by 4 minute denticles and a slightly enlarged apical tooth, giving a total dental count of 12.

Basal lamella of mandible low, triangular to rounded-triangular, not visible or partially visible in full-face view with the mandibles fully closed.

Labrum terminates in a pair of narrow digitate to conical lobes.

Clypeus with anterior margin broad, transverse to shallowly concave in full-face view.

Lateral clypeal margins approximately straight to weakly convex, and feebly convergent anteriorly. In ventral view the lateral clypeal margins extend well beyond the outer margins of the fully closed mandibles through the basal third or more of their length.

Clypeal lateral margins fringed with a continuous row of anteriorly curved spatulate to spoon-shaped hairs; anterior margin with similar but smaller hairs that are curved toward the midline. Clypeal dorsum with numerous small spatulate to spoon-shaped hairs, without any other form of pilosity.

Preocular carina conspicuous in full-face view.

Ventrolateral margin of head between eye and mandible quite sharply angular. Postbuccal impression small to vestigial.

Cuticle of side of head within scrobe reticulate or reticulate-punctate.

Scape short, SI 63-70 (in Malagasy species), conspicuously dorsoventrally flattened, the dorsum and ventre converging anteriorly so that the leading edge is a flange or even a thin lamella. Ventral surface of scape behind the leading edge usually distinctly concave.

Leading edge of scape with spatulate to spoon-shaped hairs, some or all of which are curved toward the scape base.

Pronotal dorsum without a median longitudinal carina.

Propodeum with triangular teeth sub tended by a lamella on each side that is sometimes broad and engages the teeth through most of their length.

Spongiform appendages well developed on postpetiole; ventral spongiform curtain of petiole may be well developed but in some is vestigial or absent beneath the peduncle. Base of first gastral sternite in profile with a pad of spongiform tissue.

Pilosity. Pronotal humeral hair elongate, straight or flagellate. Cephalic dorsum with curved-clavate to spoon-shaped hairs, almost suborbicular in some. Dorsolateral margins of head without freely laterally projecting elongate simple or flagellate hairs.

Sculpture. Dorsum of head behind clypeus reticulate-punctate. Pleurae, side of propodeum and disc of postpetiole smooth.

Neartic
At a glance the North American members of this group are quickly recognised by their possession of 5 principal mandibular teeth, presence of basally curved stoutly spatulate to spoon-shaped hairs on the leading edge of the scape, and presence of an anteriorly curved fringing row of stout spatulate or spoon-shaped hairs on the lateral clypeal margin. The group remains as it was conceived by Brown (1953a), with the addition of a few later described species.

Development of a mandibular diastema is morphoclinal through the group. In arizonica, californica and rostrata a diastema is absent or minute; in bunki and carolinensis it is present but short, shorter than the length of the basal tooth; finally, in chiricahua and hyalina the diastema is very conspicuous, longer than the basal tooth.

Malagasy
The four species are known only from Madagascar.