A collection was made from a colony (TI09-KY01) was collected from a lowland secondary forest on the Tunghai University campus and from a pitfall trap sampling secondary mixed evergreen broad-leaved forest.
A member of the ceylonicus group. Jaitrong and Yamane (2013) - Aenictus formosensis has been confused and synonymized with the closely related Aenictus ceylonicus, but can be distinguished from the latter as follows: mandible with 4 teeth including apical tooth (3 teeth in the latter); subpetiolar process well developed, subrectangular (weakly developed in the latter); postpetiole almost as long as high (very short, distinctly shorter than high in the latter). This species is also similar to Aenictus khaoyaiensis in having a 4-toothed mandible and smooth and shiny pronotum. However, it is separated from the latter by the well-developed subpetiolar process that is subrectangular (low, with ventral outline convex and anteroventral corner angulate in the latter).
Keys including this Species
- Key to Aenictus ceylonicus group species of China
- Key to southeastern Asian Aenictus ceylonicus group species
Distribution based on Regional Taxon Lists
Distribution based on AntMaps
Distribution based on AntWeb specimens
Check data from AntWeb
Jaitrong and Yamane (2013) - The Japanese Ant Database Group (2003) recorded two Aenictus species, i.e., Aenictus lifuiae and A. ceylonicus from the Ryukyus, Japan. The pictures labeled A. ceylonicus are most probably of Aenictus formosensis.
Little is known about the biology of Aenictus formosensis. The genus is comprised of species that live an army ant lifestyle. Aenictus typically prey on other ants, from other genera, or other insects such as wasps or termites. There are reports of Aenictus preying on other insects as well and even have been observed collecting honeydew from homopterans (Santschi, 1933; Gotwald, 1995) but this appears, at least from available evidence, to be uncommon. Foraging raids can occur day or night across the ground surface. Occasionally raids are arboreal. During a raid numerous workers attack a single nest or small area, with several workers coordinating their efforts to carry large prey items back to the nest or bivouac. Aenictus have a nomadic life style, alternating between a migratory phase in which nests are temporary bivouacs in sheltered places above the ground and a stationary phase where semi-permanent underground nests are formed. During the nomadic phase bivouacs move regularly, sometimes more than once a day when larvae require large amounts of food. Individual nests usually contain up to several thousand workers, although nest fragments containing only a few hundred workers are often encountered. Queens are highly specialised and look less like workers than in most ant species. They have greatly enlarged gasters (dichthadiform) and remain flightless throughout their life. New colonies are formed by the division of existing colonies (fission) rather than by individual queens starting colonies on their own.
Known only from the worker caste.
The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.
- formosensis. Aenictus ceylonicus var. formosensis Forel, 1913f: 188 (w.) TAIWAN. Junior synonym of ceylonicus: Wilson, 1964a: 452. Revived from synonymy and raised to species: Jaitrong & Yamane, 2013: 185.
Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.
Jaitrong and Yamane (2013) - (n = 10). TL 2.05–2.95 mm; HL 0.50–0.63 mm; HW 0.45–0.63 mm; SL 0.31–0.53 mm; ML 0.70–0.93 mm; PL 0.15–0.23mm; CI 90– 100; SI 69–84.
Head in full-face view round, slightly longer than broad (in some specimens almost as long as broad), sides convex and posterior margin almost straight or feebly concave; occipital margin lacking collar. Antennal scape reaching 2/3 of head length; antennal segments II longer than broad; III-VI each almost as long as broad; terminal segment (X) almost as long as VII+VIII+IX. Frontal carina short, reaching the level of posterior margin of torulus. Parafrontal ridge absent. Anterior clypeal margin almost straight, lacking denticles. Masticatory margin of mandible with 4 teeth, including a large apical tooth; basal margin weakly concave, lacking denticles. Maximum width of gap between anterior clypeal margin and mandibles about 2.5 times as broad as maximum width of mandible. Promesonotum convex dorsally and sloping gradually to metanotal groove; metanotal groove distinct; metapleural gland bulla relatively small, its maximum diameter about 2.7 times as long as distance between propodeal spiracle and metapleural gland bulla. Propodeum in profile with feebly convex dorsal outline; propodeal junction angulated, nearly right-angled; declivity of propodeum wide, shallowly concave, and encircled with a distinct rim. Petiole sessile and short, almost as long as high, with its dorsal outline elevated posteriorly; subpetiolar process developed, subrectangular, with anterior and posterior corners acutely angulated (posterior corner bluntly angulated in some specimens). Postpetiole somewhat smaller than petiole, with its dorsal outline convex.
Head entirely smooth and shiny. Mandible with fine longitudinal striation, except along masticatory margin smooth and shiny. Basal half of antennal scape microreticulate; apical half smooth and shiny (dorsal face); ventral face of antennal scape entirely superficially reticulate. Promesonotum smooth and shiny except anteriormost portion punctate, lateral face of pronotum partly superficially reticulate and shiny; upper portions of mesopleuron and metapleuron with approximately 10 longitudinal rugae; lower portion of mesopleuron reticulate, somewhat shiny; lower portion of metapleuron somewhat smooth and shiny (in smaller workers the smooth area extending to upper portion); lateral face of propodeum with 3-5 longitudinal rugae (not clear in smaller workers). Petiole entirely punctate but in smaller workers the dorsal face superficially shagreened to smooth and shiny; postpetiole densely punctuate with smooth and shiny dorsal face. Femora entirely smooth and shiny except basal 1/4 micropunctate; tibiae superficially sculptured but shiny.
Head and mesosoma dorsally with relatively dense standing hairs; longest pronotal hair 0.18–0.20 mm long. Head, mesosoma, petiole and postpetiole reddish brown; gaster, antenna and legs yellowish brown, paler than head, mesosoma and waist; mandible dark brown.
Jaitrong and Yamane (2013) - Aenictus ceylonicus var. formosensis: two syntype workers from Taiwan, Taihorin (not examined).
- Syntype, 2 workers, Taihorin, Taiwan.