Aenictus silvestrii

Aenictus silvestrii
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Dorylinae
Genus:	Aenictus
Species:	A. silvestrii
Binomial name
Aenictus silvestrii Wheeler, W.M., 1929 Specimen Labels

Specimens from Sabah were found marching on the forest floor in a primary rainforest.

Identification

A member of the silvestrii species group. Aenictus silvestrii is very unique in having the head and mesosoma with rugae which are absent in the other species of the group, but it has the same number of antennal segments (9) as has Aenictus jarujini.

Keys including this Species

• Key to Aenictus silvestrii group species

Distribution

Malay Peninsula and Borneo (Sabah and Brunei)

Distribution based on Regional Taxon Lists

Indo-Australian Region: Borneo, Indonesia, Malaysia (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 Aenictus biology  Little is known about the biology of Aenictus silvestrii. 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. ‎

Castes

Wilson 1964 Army Ant fig 76-83

Known only from the worker caste.

Nomenclature

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

• silvestrii. Aenictus (Paraenictus) silvestrii Wheeler, W.M. 1929g: 28, fig. 1 (w.) WEST MALAYSIA.
  • Type-material: 2 syntype workers.
  • Type-locality: Malaysia: Penang Island (F. Silvestri).
  • Type-depository: MCZC.
  • Status as species: Chapman & Capco, 1951: 12; Wilson, 1964a: 479; Bolton, 1995b: 60; Jaitrong & Yamane, 2010: 331 (redescription); Pfeiffer, et al. 2011: 32.
  • Distribution: Brunei, Malaysia (Peninsula, Sabah).

Description

Jaitrong and Yamane (2010) - The measurement of a syntype after Wilson (1964): HL 0.92 mm; HW 0.83 mm; SL 0.59 mm. HW of 2nd syntype 0.80 mm. Nontype material (n = 4): TL 3.9–4.1 mm; HL 0.87–0.93 mm; HW 0.82–0.85 mm; SL 0.50–0.57 mm; ML 1.25–1.3 mm; MTL 0.6–0.63 mm; PL 0.30–0.35 mm; CI 89–94; SI 61–70.

worker: a) in profile; b) mandible

Head in full-face view subrectangular, slightly longer than broad, with feebly convex sides; posterior margin of head almost straight but weakly sinuate; occiput bearing a narrow collar with irregular carinae. Antenna 9-segmented (in some nontype specimens segment III is clearly demarcated from IV, though in the two syntypes this segmentation is not very clear); antennal segment II small, nearly as long as broad; III very short, broader than long; IV nearly as long as broad; V and VI distinctly longer than broad; VII and VIII as long as broad; the last (IX) longer than broad and much longer than others, almost as long as VII and VIII combined. Frontal carinae short extending less than half length of head, very poorly developed in posterior half. Clypeus short and roundly produced anteriorly, lacking anterior teeth. Mandible with apical tooth large and curved, followed by a series of 10–15 denticles of two sizes, the larger alternating with 2–3 of smaller; basal margin of mandible with 3–4 small denticles. With mesosoma seen in profile promesonotum weakly convex dorsally and sloping gradually to metanotal groove; dorsal outline of propodeum almost straight. Propodeal junction acutely angulate; declivity of propodeum shallowly concave, encircled with a rim. Petiole slightly longer than broad, relatively low, nearly as high as long, anteriorly and posteriorly margined with a rim similar to that of propodeum but poorly developed; subpeiolar process very low; postpetiole as long as petiole in profile roundly convex above, anteroventrally produced as a blunt angle directed downward and forward. Gaster elongate-elliptical, narrowed anteriorly and posteriorly.

Head extensively with regular rugae and dense minute punctures on rugae; rugae on lateral and ventral faces of head longitudinal, but those on vertex transverse and those on frons curved outwardly. Mandible except in apical portion and along masticatory margin, and antennal scape wholly with dense small punctures. Dorsum of mesosoma, pro-and mesopluron with regular longitudinal rugae. Node of petiole with irregular longitudinal carinae and dense small punctures; postpetiole with similar sculpture but carinae weaker than on petiole.

Gaster smooth and shining except for extreme base. Fore coxa distinctly punctate; narrow basal portions of femora distinctly sculptured and mat; other parts of legs largely smooth.

Body with relatively sparse standing hairs mixed with sparse short hairs over the surface; length of the longest pronotal hair approximately 0.20 mm. Head, mesosoma and waist reddish brown to dark brown; mandible dark brown; antenna reddish brown, with the apical segment paler; gaster and legs largely yellowish brown; narrow basal potions of femora darkened.

Type Material

Jaitrong and Yamane (2010) - Two syntype workers from Penang Island, Malay Peninsula deposited in Museum of Comparative Zoology (examined).

References

• Jaitrong, W. and Yamane, S. 2010. The army ant Aenictus silvestrii and its related species in Southeast Asia, with a description of a new species (Hymenoptera: Formicidae: Aenictinae). Entomological Science. 13:328-333.
• Borowiec, M.L. 2019. Convergent evolution of the army ant syndrome and congruence in big-data phylogenetics. Systematic Biology 68, 642–656 (doi:10.1093/sysbio/syy088).
• Cantone S. 2018. Winged Ants, The queen. Dichotomous key to genera of winged female ants in the World. The Wings of Ants: morphological and systematic relationships (self-published).
• Wheeler, W. M. 1929h. Ants collected by Professor F. Silvestri in Formosa, the Malay Peninsula and the Philippines. Boll. Lab. Zool. Gen. Agrar. R. Sc. Super. Agric. 24: 27-64 (page 28, fig. 1 worker described)
• Wilson, E. O. 1964a. The true army ants of the Indo-Australian area (Hymenoptera: Formicidae: Dorylinae). Pac. Insects 6: 427-483 (page 479, see also)
• Yamane, S., Tanaka, H.O., Hasimoto, Y., Ohashi, M., Meleng, P., Itioka, T. 2021. A list of ants from Lambir Hills National Park and its vicinity, with their biological information: Part II. Subfamilies Leptanillinae, Proceratiinae, Amblyoponinae, Ponerinae, Dorylinae, Dolichoderinae, Ectatomminae and Formicinae. Contributions from the Biological Laboratory, Kyoto University 31, 87–157.

References based on Global Ant Biodiversity Informatics

• Jaitrong, W.; Yamane, S. 2010. The army ant Aenictus silvestrii and its related species in Southeast Asia, with a description of a new species (Hymenoptera: Formicidae: Aenictinae). Entomological Science 13:328-333.
• Pfeiffer M.; Mezger, D.; Hosoishi, S.; Bakhtiar, E. Y.; Kohout, R. J. 2011. The Formicidae of Borneo (Insecta: Hymenoptera): a preliminary species list. Asian Myrmecology 4:9-58