Syllophopsis hildebrandti

Syllophopsis hildebrandti is found in all native habitats. Sifting of litter appears to be the most effective sampling method. Nest series have been taken from rotted tree stumps and other wood substrates, and from under stones. (Heterick 2006)

Identification
By far the most abundant member of the S. hildebrandti group on Madagascar, this species varies more than any other Malagasy Syllophopsis. Fortunately, the pattern of variation shows a clinal pattern, unlike that in Monomorium termitobium, making its analysis somewhat easier. The species, as it is understood here, is closely related to the very similar Syllophopsis fisheri, and may occasionally hybridize with that species (see Syllophopsis adiastolon). The petiolar node, although it varies greatly, is still the best means of separating workers of S. hildebrandti from those of S. fisheri, but in doubtful cases the other features mentioned in the key should be carefully examined. In the former the node has a posterior face that is rarely vertical, and its dorsum usually retains some degree of asymmetry. The latter species has a symmetrical node with a vertical posterior face. Thick, tapering nodes in some populations of S. hildebrandti tend to possess faint longitudinal striolae absent in S. fisheri. Workers of S. hildebrandti have a maximum of four mandibular teeth, and that will help to distinguish them from those S. fisheri workers that have a five-toothed mandible. Several of the more conspicuous morphotypes of S. hildebrandti have a well-defined range. A form whose large, robust, reddish workers possess a longitudinally striolate petiolar node is perhaps the most distinctive. The eye can be relatively large in workers of this morphotype, with up to 30 or more ommatidia. Unlike the similarly large-eyed S. adiastolon, this morphotype has a narrow, high postpetiole. This ant is found along the entire western and southern coast of Madagascar, excluding only the extreme north-west. The queen has a distinctive postpetiole that is vertically strongly attenuate and produced laterally, and is otherwise more heavily sculptured than the typical S. hildebrandti queen. Some individual workers of this form show actual physical convergence with the smaller yellow worker of the common morphotype, the head and pronotal sector being that of the smaller morphotype, while the propodeum and nodes are those of the robust red morphotype! In the extreme north of Antsiranana Province and on Nosy Be Island, is another, yellow morphotype in which the anteroventral postpetiolar process is very large and terminates in a conspicuous carina. Further south in Antsiranana and parts of Toamasina is a similar form, whose workers are very smooth and have an elongate peduncle. The workers lack the large anteroventral petiolar process of the more northern populations. In some cases the petiolar node of individual workers from both groups is strongly asymmetrical and very low. Colonies with red-and-yellow workers, similar in appearance to Syllophopsis gongromos, occur in Fianarantsoa Province among colonies with more unobtrusive yellow workers. The CAS has a number of queens and males for this morphotype, and the holotype queen, from “Central Madagascar”, belongs to the same population. Ergatoids may be paler than fully developed queens. The large workers of yet another morphotype in Antananarivo and Antsiranana Provinces are very similar to workers of morphotype (b) of S. fisheri and have a similar node, which, however, usually has a slightly asymmetrical dorsum and a few weak striolae on the sides.

The most commonly seen worker of S. hildebrandti is a small, depigmented yellow, through bright yellow to yellowish-brown ant with very small eyes (as few as five ommatidia) and a petiolar node that varies from rounded and smooth to more attenuate and sculptured. In brownish specimens the head may be darker than the mesosoma in dorsal view. Workers with this appearance are found in many parts of inland Madagascar.

Distribution based on Regional Taxon Lists
Afrotropical Region: Central African Republic, Comoros. Malagasy Region: Madagascar, Mayotte.

Nomenclature

 *  hildebrandti. Monomorium minutum r. hildebrandti Forel, 1892l: 256 (q.) MADAGASCAR. Santschi, 1926b: 237 (w.); Heterick, 2006: 174 (m.). Combination in Syllophopsis: Ward et al., 2014: 13. Subspecies of minutum: Wheeler, W.M. 1922a: 1027. Raised to species: Dalla Torre, 1893: 67; Bolton, 1995b: 262. See also: Heterick, 2006: 171.

Worker
Heterick (2006) - HML 1.18–2.12 HL 0.44–0.73 HW 0.36–0.61 CeI 75–86 SL 0.30–0.54 SI 82–102 PW 0.25–0.47 (n=40).

HEAD: Head oval; vertex planar or weakly concave; frons shining and smooth except for piliferous pits; pilosity of frons a mixture of incurved, semi-erect setae and slightly shorter decumbent setae. Eye moderate, eye width 1–1.5× greatest width of antennal scape to small, eye width less than 1× greatest width of antennal scape; (in full-face view) eyes set at about midpoint of head capsule to set below midpoint of head capsule; (viewed in profile) eyes set posteriad of midline of head capsule; eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin; Antennal segments 12; antennal club three-segmented. Clypeal carinae always well-defined; anteromedian clypeal margin emarginate, clypeal carinae terminating in blunt angles; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin extending slightly beyond level of posterior margin of antennal fossae. Anterior tentorial pits equidistant from antennal fossae and mandibular insertions. Frontal lobes straight, parallel. Psammophore absent. Palp formula 2,2. Mandibular teeth four; mandibles linear-triangular and smooth (except for piliferous pits); masticatory margin of mandibles strongly oblique; basal tooth approximately same size as t3 (four teeth present).

MESOSOMA: Promesonotum shining and mainly smooth, vestigial striolae, if present, confined to lower anterior mesopleuron, or, shining and smooth on dorsum, entire lower mesopleuron distinctly striolate; (viewed in profile) anterior promesonotum smoothly rounded, thereafter more-or-less flattened, promesonotum on same plane as propodeum; promesonotal setae greater than twelve; standing promesonotal setae consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae; appressed promesonotal setulae few, mainly on dorsum of promesonotum. Metanotal groove absent. Propodeum shining, dorsum and sides of propodeum mainly smooth, with weak to strong striolae on declivitous face and on metapleuron; propodeal dorsum slightly elevated anteriad and sloping away posteriad, propodeal angles not raised, or, sloping posteriad, and depressed between raised propodeal angles; propodeum smoothly rounded or with indistinct angle, or, angulate, propodeal angle blunt; standing propodeal setae consisting of two or more prominent pairs anteriad, often with another pair of prominent setae posteriad, and other smaller setae on/around dorsal and declivitous surfaces of propodeum; appressed propodeal setulae very sparse or absent; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum to nearer declivitous face of propodeum than metanotal groove. Vestibule of propodeal spiracle distinct. Propodeal lobes present as blunt-angled flanges, or, present as rounded flanges.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated well anteriad of petiolar node, or, lateral and situated slightly anteriad of petiolar node; node (viewed in profile) cuneate, vertex rounded, or, conical, vertex rounded, or, tumular, inclined posteriad, with vertex also tapered posteriad, or, subcuboidal, vertex rounded; appearance of node shining and smooth throughout, or, shining and longitudinally striolate; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1; anteroventral petiolar process present as a thin flange tapering posteriad, or, absent or vestigial; ventral petiolar lobe present, or, present, but weakly developed to vestigial; height ratio of petiole to postpetiole about 1:1; height–length ratio of postpetiole between 4:3 and 1:1; postpetiole shining and smooth, or, shining and weakly striolate posteriad; postpetiolar sternite depressed near its junction with gaster, and sloping anteriad at angle of 45–60 to form large conspicuous lip at its anterior end, or, depressed at about its center, with anterior process developed as a short, conspicuous spur angled at 45–90, or, not depressed at midpoint, its anterior end an inconspicuous lip or small carina.

GASTER: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.

GENERAL CHARACTERS: Color highly variable; from uniform pale yellow to light brown, often with yellow or yellowish-brown head and appendages and yellowish-brown to brown gaster, contrasting with reddish-orange mesosoma and nodes. Worker caste monomorphic within nests, but with large internidal and inter-population variation in size and sculpture.

Queen
Heterick (2006) - Holotype: Not taken, as the queen lacks crucial body parts, including the head.

(non-types): HML 3.21–4.13 HL 0.96–1.06 HW 0.92–1.06 CeI 92–101 SL 0.82–0.96 SI 84–99 PW 0.92–1.11 (n=19).

HEAD: Head square, or, rectangular; vertex weakly concave or planar; frons shining and smooth except for piliferous pits and a few striolae around antennal sockets and frontal carinae, or, shining and longitudinally striolate in left and right sectors and medially smooth; pilosity of frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter setae or setulae, which are decumbent or appressed, longer setae thickest on vertex. Eye ovoid, narrowed posteriad; (in full-face view) eyes set above midpoint of head capsule, or, set at about midpoint of head capsule; (viewed in profile) eyes set posteriad of midline of head capsule.

MESOSOMA: Mesoscutum broadly convex, or, broadly convex anteriad, convexity reduced posteriad; pronotum, mesoscutum and mesopleuron shining and mainly smooth, vestigial striolae, if present, confined to anterior katepisternum; length–width ratio of mesoscutum and scutellum combined between 2:1 and 3:2 to between 3:2 and 4:3; axillae separated by width of at least one axilla, or, narrowly separated (i.e., less than width of one axilla); standing pronotal/mesoscutal setae consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae; appressed pronotal, mescoscutal and mesopleural setulae few, mainly on sides of pronotum and mesopleuron. Propodeum shining, dorsum and sides of propodeum mainly smooth, with weak to strong striolae on declivitous face and on metapleuron; propodeum distinctly angulate, propodeal angle sharp to distinctly angulate, propodeal angles produced as short denticles; propodeal dorsum sloping posteriad, and depressed between raised propodeal angles; standing propodeal setae variable, from absent to up to a dozen or more longer erect and shorter sub-erect setae; appressed propodeal setulae well-spaced and sparse, or, very sparse or absent; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum; propodeal lobes present as well-developed, rounded flanges, or, present as bluntly angled flanges.

WING: Wing veins tubular and strongly sclerotised; vein m–cu present as an entire vein enclosing first discoidal cell; vein cu–a present.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated well anteriad of petiolar node, or, lateral and situated slightly anteriad of petiolar node; node (viewed in profile) cuneate, vertex tapered; appearance of node shining and weakly striolate posteriad; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 4:3 and 1:1; anteroventral petiolar process absent or vestigial; height ratio of petiole to postpetiole between 4:3 and 1:1; height–length ratio of postpetiole between 3:2 and 4:3; postpetiole shining, smooth anteriad, weakly to strongly striate posteriad; postpetiolar sternite depressed at about its centre, anterior carina usually inconspicuous.

GASTER: Pilosity of first gastral tergite consisting of a mixture of incurved, erect and semi-erect setae and slightly shorter decumbent setae.

GENERAL CHARACTERS: Color of smaller specimens usually yellowish or brown, larger specimens variegated yellowish-brown/brown. Brachypterous alates not seen. Ergatoid or worker-female intercastes seen.

Male
Heterick (2006) - HML 1.44–1.75 HL 0.43–0.54 HW 0.41–0.53 CeI 83–104 SL 0.07–0.13 SI 13–28 PW 0.37–0.56 (n=12).

HEAD: (In full-face view) head width–mesosoma width ratio between 1:1 and 3:4; frons finely micropunctate. Compound eyes protuberant and weakly ovoid; margin of compound eye clearly separated from posterior margin of clypeus. Ocelli not turreted. Ratio of length of first funicular segment of antenna to second funicular segment between 3:4 and 2:3. Maximum number of mandibular teeth and denticles four.

MESOSOMA: Mesoscutum broadly convex with a few vestigial striolae on its dorsum, otherwise pronotum and mesoscutum smooth and shining; parapsidal furrows distinct; notauli absent; axillae separated by width of at least one axilla.

WING: Wing veins tubular and strongly sclerotised; vein m–cu present as an entire vein enclosing entire discoidal cell; vein cu–a present.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated well anteriad of petiolar node to laterodorsal and situated well anteriad of petiolar node; node (viewed in profile) conical, vertex tapered; appearance of node shining, with vestigial sculpture; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 4:3; anteroventral petiolar process absent or vestigial; height ratio of petiole to postpetiole between 3:2 and 4:3; height–length ratio of postpetiole between 4:3 and 1:1; postpetiole shining and smooth.

GASTER: Pilosity of first gastral tergite consisting of a mixture of incurved, semi-erect setae and slightly shorter decumbent setae.

GENERAL CHARACTERS: Color reddish brown, head chocolate.

Type Material
Holotype: (See comments under M. shuckardi, though, due to its damaged condition, this specimen could not be measured.) Queen, Madagascar, central Madagascar. The published description of the queen mentions that a Mr. Hildebrand was the collector. The type specimen lacks head, postpetiole and gaster. A‘type’ from Madagascar described by Santschi (1926) as the worker of M. hildebrandti is actually a specimen of Monomorium madecassum Forel.

References based on Global Ant Biodiversity Informatics

 * Ettershank G. 1966. A generic revision of the world Myrmicinae related to Solenopsis and Pheidologeton (Hymenoptera: Formicidae). Aust. J. Zool. 14: 73-171.
 * Fisher B. L. 1997. Biogeography and ecology of the ant fauna of Madagascar (Hymenoptera: Formicidae). Journal of Natural History 31: 269-302.
 * Fisher B. L. 2003. Formicidae, ants. Pp. 811-819 in: Goodman, S. M.; Benstead, J. P. (eds.) 2003. The natural history of Madagascar. Chicago: University of Chicago Press, xxi + 1709 pp.
 * Heterick B. 2006. A Revision of the Malagasy Ants Belonging to Genus Monomorium Mayr, 1855 (Hymenoptera: Formicidae). Proceeding of the California Academy of Sciences (PCAS) 57: 69-202
 * Santschi F. 1926. Description de nouveaux Formicides éthiopiens (IIIme partie). Revue Zoologique Africaine (Brussels) 13: 207-267.