Strumigenys jacobsoni

Strumigenys jacobsoni
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Myrmicinae
Tribe:	Attini
Genus:	Strumigenys
Species group:	leptothrix
Species complex:	elegantula
Species:	S. jacobsoni
Binomial name
Strumigenys jacobsoni Menozzi, 1939 Specimen Labels

Known from a few wet forest and swamp collections, with each being collected from litter/ground sampling. Tang & Guenard (2023) report it in secondary forest, mature forest and rubber plantation.

Photo Gallery

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  Fig. 2. Mandible close-ups of workers from the elegantula-complex in the Strumigenys leptothrix-group. A–B. S. intermedia (TT01353). C. S. elegantula from Hong Kong (RHL00290). D. S. jacobsoni from Vietnam (ANTWEB1011973).
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  Tang & Guenard (2023), Fig. 23. New species records of Strumigenys in full-face, profile and dorsal views. A–C. Worker of S. inhonesta from Thailand (ANTWEB1011945). D–F. Worker of S. jacobsoni from Vietnam (ANTWEB1011973). G–I. Worker of S. juliae from Thailand (KCW-S08-sp03).

Identification

Tang & Guenard (2023) - A member of the elegantula complex in the Strumigenys leptothrix-group. After careful examination of the species’ dentition, using specimens with opened mandibles, we determined that S. jacobsoni belongs to the newly introduced elegantula-complex in the S. leptothrix group (Fig. 2D). Specimens from other localities should be checked if they share similar morphology.

Bolton (2000) - A very distinctive densely hairy species, jacobsoni shares its propodeal structure, as described under Strumigenys leptothrix, with a number of other species of the region. Of these jacobsoni and leptothrix have abundant standing hairs on the cephalic dorsum, arising all over the surface from the posterior clypeal margin to the occipital margin and very conspicuous in profile. Both species also have straight freely projecting pilosity on the hind tibiae, a feature shared with Strumigenys alecto and Strumigenys elegantula, but in the last two species standing hairs on the dorsum of the head are restricted to the posterior portion. Apart from this the separation of alecto and elegantula from jacobsoni may easily be confirmed: alecto lacks pronotal margination (very conspicuous in jacobsoni), and elegantula has the mesopleuron uniformly densely reticulate-punctate and the pronotal dorsum lacks standing hairs (mesopleuron not reticulate-punctate in jacobsoni and pronotum with abundant standing hairs). S. jacobsoni separates from leptothrix as follows.

S. jacobsoni: SI < 75 (range 68-71). Leading edge of scape lacking straight projecting stiff simple hairs. Vertex predominantly longitudinally rugulose. With head in profile apex of occipital lobe projecting posteriorly as a thick flange separating curvatures of dorsal and ventral surfaces. Pronotum sharply marginate dorsolaterally, dorsum flat to concave; lateral faces of pronotum not projecting beyond marginations in dorsal view. Mesopleuron with at least vestiges of sculpture. Propodeal spines long, the lamellae broad. Dorsal outline of petiole in profile with peduncle grading into node through an evenly convex curve; node without a differentiated anterior face.

S. leptothrix: SI > 75 (range 79-80). Leading edge of scape with straight projecting stiff simple hairs. Vertex predominantly reticulate-punctate. With head in profile apex of occipital lobe more or less evenly rounded, not forming a thick posteriorly projecting flange. Pronotum weakly marginate dorsolaterally, dorsum shallowly convex; lateral faces of pronotum projecting beyond marginations in dorsal view. Mesopleuron completely smooth. Propodeal spines reduced to triangular teeth, the lamellae narrow. Dorsal outline of petiole in profile with peduncle separated from dorsum of node by a short but distinctly defined anterior nodal face.

Keys including this Species

• Key to Strumigenys of East Asia (as Pyramica)

Distribution

The record of S. jacobsoni in southern Vietnam indicates that this species could be much more widespread throughout the Indochinese Peninsula than currently known. Its presence in neighboring countries such as Cambodia and Thailand is likely (Tang & Guenard, 2023).

Distribution based on Regional Taxon Lists

Indo-Australian Region: Indonesia (type locality), Malaysia, Philippines.
Oriental Region: Vietnam.

Distribution based on AntMaps

Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.

Biology

Explore Overview of Strumigenys biology  Strumigenys were once thought to be rare. The development and increased use of litter sampling methods has led to the discovery of a tremendous diversity of species. Many species are specialized predators (e.g. see Strumigenys membranifera and Strumigenys louisianae). Collembola (springtails) and other tiny soil arthropods are typically favored prey. Species with long linear mandibles employ trap-jaws to sieze their stalked prey (see Dacetine trap-jaws). Larvae feed directly on insect prey brought to them by workers. Trophallaxis is rarely practiced. Most species live in the soil, leaf litter, decaying wood or opportunistically move into inhabitable cavities on or under the soil. Colonies are small, typically less than 100 individuals but in some species many hundreds. Moist warm habitats and micro-habitats are preferred. A few better known tramp and otherwise widely ranging species tolerate drier conditions. Foraging is often in the leaf litter and humus. Workers of many species rarely venture above ground or into exposed, open areas. Individuals are typically small, slow moving and cryptic in coloration. When disturbed individuals freeze and remain motionless. Males are not known for a large majority of species. ‎

Castes

Worker

.	Owned by Museum of Comparative Zoology.

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

• jacobsoni. Strumigenys (Cephaloxys) jacobsoni Menozzi, 1939b: 180, fig. 4 (w.) INDONESIA (Sumatra). Brown, 1949d: 8 (q.). Combination in Smithistruma: Brown, 1948e: 105; in Weberistruma: Brown, 1949d: 8; in Pyramica: Bolton, 1999: 1673; in Strumigenys: Baroni Urbani & De Andrade, 2007: 122. See also: Bolton, 2000: 433.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Bolton (2000) - HL 0.68-0.78, HW 0.47-0.52, CI 67-71, ML 0.08-0.10, MI 12-14, SL 0.32-0.37, SI 68-71 (6 measured). Cephalic dorsum in profile densely clothed with elongate simple standing hairs that arise all over the surface from close to the posterior clypeal margin to the occipital margin, but are absent from the clypeus. In full-face view the dorsolateral margin of the head has numerous long fine freely projecting hairs throughout its length. Leading edge of scape with fine curved hairs that are directed toward the apex, without stiffly projecting straight hairs. Dorsum of head with scattered irregular longitudinal fine rugulae, the vertex also with weak punctulate sculpture present. Dentition discussed in introduction to group. Pronotum sharply marginate dorsolaterally, the dorsum transversely approximately flat to shallowly concave and its margins equipped with numerous long fine projecting hairs along their entire length. Mesopleuron not reticulate-punctate; sometimes more or less smooth but usually with traces of weak transverse rugulae. Dorsal surfaces of alitrunk, waist and gaster with abundant long fine standing hairs that are acute apically. All segments of legs with numerous very long fine projecting hairs that are erect to suberect and straight to feebly curved. The longest tibial hairs are very much longer than the maximum tibial width. Propodeum with a pair of spines that are subtended by broad lamellae, the latter merging into broadly rounded lamellate propodeal lobes at the base of the declivity. Spongiform appendages of waist well developed, the lateral lobe of the petiole very broad and extending far forward along the side of the node. Sculpture of pronotal dorsum variable; sometimes the surface completely smooth but more usually with some faint, almost effaced, punctation, very weak longitudinal rugulae, or both. Disc of postpetiole smooth.

Type Material

Bolton (2000) - Syntype workers, INDONESIA: Sumatra, Fort de Kock (E. Jacobson) (Museum of Comparative Zoology) [examined].

References

• Baroni Urbani, C. & De Andrade, M.L. 2007. The ant tribe Dacetini: limits and constituent genera, with descriptions of new species. Annali del Museo Civico di Storia Naturale “G. Doria” 99:1-191.
• Bolton, B. 1998b. A preliminary analysis of the ants of the Pasoh Forest Reserve. Pp. 84-95 in: Lee, S. S.; Dan, Y. M.; Gauld, I. D.; Bishop, J. (eds.) Conservation, management and development of forest resources. Proceedings of the Malaysia-United Kingd (page 92, combination in Trichoscapa)
• Bolton, B. 1999. Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae). J. Nat. Hist. 3 33: 1639-1689 (page 1673, combination in Pyramica)
• Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028. (page 433, redescription of worker)
• Brown, W. L., Jr. 1948e. A preliminary generic revision of the higher Dacetini (Hymenoptera: Formicidae). Trans. Am. Entomol. Soc. 74: 101-129 (page 105, combination in Smithistruma)
• Brown, W. L., Jr. 1949f. Revision of the ant tribe Dacetini. I. Fauna of Japan, China and Taiwan. Mushi 20: 1-25 (page 8, combination in Weberistruma, description of queen)
• Menozzi, C. 1939b. Qualche nuova formica di Sumatra. Tijdschr. Entomol. 82: 175-181 (page 180, fig. 4 worker described)
• Musfira, S.H., Rafi, M., Gusti, M., Putri, D.H., Satria, R. 2022. New data on the genus Strumigenys (Hymenoptera: Formicidae) from Sumatra. Zoosystematica Rossica 31(1): 74–86 (doi:10.31610/zsr/2022.31.1.74).
• Tang, K. L., Guénard, B. 2023. Further additions to the knowledge of Strumigenys (Formicidae: Myrmicinae) within South East Asia, with the descriptions of 20 new species. European Journal of Taxonomy 907, 1–144 (doi:10.5852/ejt.2023.907.2327).

References based on Global Ant Biodiversity Informatics

• Brown W. L., Jr. 1949. Revision of the ant tribe Dacetini. I. Fauna of Japan, China and Taiwan. Mushi 20: 1-25.
• Chapman, J. W., and Capco, S. R. 1951. Check list of the ants (Hymenoptera: Formicidae) of Asia. Monogr. Inst. Sci. Technol. Manila 1: 1-327
• Menozzi C. 1939. Qualche nuova formica di Sumatra. Tijdschrift voor Entomologie 82: 175-181.