Strumigenys dexis

Strumigenys dexis
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Myrmicinae
Tribe:	Attini
Genus:	Strumigenys
Species:	S. dexis
Binomial name
Strumigenys dexis Fisher, 2000 Specimen labels

Known from rainforest, montane forest and littoral forest, all of the records of this species have been collected from litter samples.

Identification

Bolton (2000) - A member of the dexis complex in the Strumigenys dexis-group. Within the group dexis is related to Strumigenys coveri, Strumigenys gorgon, Strumigenys peyrierasi and Strumigenys rabesoni, a complex of five species that share a distinctive form of sculpture in which cephalic and promesonotal punctures are spaced out and separated by areas of smooth cuticle, rather than having the entire surface opaque and blanketed with reticulate- punctate sculpture (promesonotal punctures absent in Strumigenys carolinae). Of these five species dexis is identified by its relatively short mandibles, broad head and unique labrum, where both anterior lobes sport a single fan-like lamella of very thin translucent cuticle that projects anteriorly. In addition:

1 The petiole node in coveri is as long as or longer than broad in dorsal view (distinctly broader than long in dexis).

2 The head has large spoon-shaped hairs on the dorsum of the occipital lobes in gorgon (absent in dexis).

3 The punctate sculpture of the vertex is much denser and more crowded in rabesoni than in dexis.

4 The mesonotum has a single pair of short straight standing hairs in peyrierasi (absent in dexis).

The presence of dense blanketing reticulate-punctate sculpture on the dorsum of the head distinguishes the sylvaini-complex from dexis and its immediate allies discussed above. Beside the sculpture Strumigenys alperti and carolinae have a unique distribution of scale-like hairs anteriorly on the cephalic dorsum, and Strumigenys sylvaini and Strumigenys wardi have standing hairs on the head and body, neither of which occurs in the four species of the dexis-complex.

Keys including this Species

• Key to Malagasy Strumigenys

Distribution

Latitudinal Distribution Pattern

Latitudinal Range: -18.695° to -18.695°.

North Temperate	North Subtropical	Tropical	South Subtropical	South Temperate

• Source: AntMaps

Distribution based on Regional Taxon Lists

Malagasy Region: Madagascar (type locality).

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. ‎

Nomenclature

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

• dexis. Strumigenys dexis Fisher, in Bolton, 2000: 641, figs. 387, 412 (w.) MADAGASCAR.

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

Description

Worker

Holotype. TL 2.4, HL 0.66, HW 0.57, CI 88, ML 0.12, MI 18, SL 0.29, SI 51, PW 0.36, AL 0.68. Characters of dexis-complex. Transverse edge of the depressed proximodorsal area of mandible with a short row of curved spoon-shaped hairs approximately the same as those fringing the upper scrobe margin. Each labral lobe terminates anteriorly in a broad fan-shaped lamella of thin translucent cuticle and a short trigger-hair mesad of fan-like lamella; trigger-hairs often difficult to see. Clypeal dorsum with minute appressed hairs, the lateral margins with a short row of anteriorly curved large spoon- shaped hairs. Upper scrobe margin in full-face view with a continuous row of anteriorly curved spoon-shaped hairs that are similar to those on the leading edge of the scape; the row ends at the apex of the scrobe and does not extend onto the side of the occipital lobe. Eye with 7 ommatidia in total. Cephalic dorsum without standing hairs of any description but with scattered minute flattened appressed hairs present. Area of cuticle within antennal scrobe densely reticulate-punctate except for extreme posterior portion which is superficially reticulate to smooth. Dorsum of head behind clypeus with separated shallow punctures, the spaces between them shining; ventral surface of head unsculptured. Pronotum in dorsal view with strongly convex sides, appearing very short and broad. Flattened dorsum of pronotum sculptured as vertex; pleurae and sides of propodeum smooth and shining; propodeal declivity with a band of fine punctate sculpture between the teeth. Lamella of propodeum broad and sinuate, apices of propodeal teeth free. Dorsal surfaces of alitrunk, waist segments and first gastral tergite without standing hairs, but minute appressed flattened hairs are sparsely present everywhere except on first gastral tergite. Base of first gastral sternite and posterior margins of petiole and postpetiole, with a row of flat, broad, spatulate appressed hairs. Petiole node in dorsal view broader than long, with extensive lateral spongiform lobes. Disc of postpetiole completely surrounded by spongiform tissue in dorsal view; sides and posterior margin of the disc forming a single convex arc and the disc with scattered but easily visible punctures upon a smooth surface. In profile all spongiform lobes of the waist segments well developed. Legs with spatulate to scale-like hairs present, but without standing pilosity.

Paratypes. TL 2.4-2.5, HL 0.65-0.66, HW 0.58-0.59, CI 88-90, ML 0.12-0.13, MI 18-20, SL 0.29, SI 49-50, PW 0.36-0.37, AL 0.68 (2 measured). As holotype.

Members of these series tend to be a little larger than the type-series and to have the head fractionally broader, HL 0.68-0.70, HW 0.63-0.64, CI 90-93, ML 0.12-0.13, MI 17-19, but otherwise match the types perfectly.

Type Material

Holotype worker, Madagascar: 45 km. S Ambalavao, 22°13'S, 47°01'E, 785 m., 25.ix.1993, sifted litter (leaf mold, rotten wood), rainforest, #696 (40)-6 (B. L. Fisher) (Museum of Comparative Zoology).

Paratypes. 1 worker with same data as holotype; 1 worker with same data but #696 (20)-9 (South African Museum, The Natural History Museum).

References

• Fisher, B.L. 2000. The Malagasy fauna of Strumigenys. Pp. 612-696 in: Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028. (page 641, worker described)

References based on Global Ant Biodiversity Informatics

• Bolton, B. 2000. The Ant Tribe Dacetini. Memoirs of the American Entomological Institute 65
• 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.