|Based on Blaimer et al., 2016. Note only selected Acropyga species are included, and undescribed species are excluded.|
Even though the species is found in savanna type habitat in many places across its range, A. silvestrii apparently does not overlap with Acropyga arnoldi, which is found exclusively in southern Africa. (LaPolla 2004)
LaPolla (2004) - Worker: Antennae 11-10 segmented; head distinctly longer than broad; head width not greater than 0.5 mm; in lateral view pronotum with short shelf; mesosomal dorsum flat, with appressed hairs. Queen: unknown. Male: unknown. Compare with Acropyga arnoldi and Acropyga paleartica.
This species can be easily separated from Acropyga arnoldi by its size (A. silvestrii TL: 1.6-2.1; HW: 0.383-0.454 versus A. arnoldi TL: 2.1-2.4; HW: 0.517-0.619). Differentiation from Acropyga paleartica can be slightly more difficult, though the torulae of A. silvestrii are very closely set together (almost touching medially) and their mandibles do not have offset basal teeth.
The relationship of this species to A. arnoldi is unclear since males remain unknown. A. silvestrii is observed with up to 7 teeth, but has not been observed with at least a 4-segmented maxillary palp as in A. arnoldi and A. paleartica.
Keys including this Species
Distribution based on Regional Taxon Lists
LaPolla (2004) - The distribution of A. silvestrii stretches from western Africa as far south and east as northern Tanzania. This is the only Acropyga known from the rainforests of Africa, which is interesting because in other areas where rainforests are found the diversity of Acropyga is substantially higher. The low species diversity found in Africa may be an artifact of collecting since there are few collections from Africa (particularly West Africa) available for study, or may indicate something of biological interest.
Distribution based on AntMaps
Distribution based on AntWeb specimens
Check data from AntWeb
The species is found in a variety of habitats from tropical savannas to rainforests; it has also been collected from cacao plantations. It has been recorded from elevations up to 1600 m.
Little is known about Acropyga silvestrii. Until further studies reveal more about this species we can infer that its natural history and biology should be similar to other Acropyga. LaPolla published a worldwide revision of the Acropyga in 2004 and the following synopsis is based on this excellent treatment of the genus.
In overall appearance Acropyga are small, robust, yellowish ants possessing a thin, easily collapsible cuticle. The species generally appear rather similar to each other morphologically. In some species workers and queens display an unusual range of phenotypic variation. Antennal segment number, for example, can vary within and between species. Even a single specimen may posses antennae with a different number of antennal segments and workers in numerous species possess one more antennal segment than conspecific males.
The small eyes, reduced antennae segmentation, lightly pigmented cuticle, and hairs covering the cuticle of Acropyga species are suggestive of a completely subterranean existence. Species also display photophobic behavior (Weber, 1944; LaPolla et al., 2002). Acropyga can survive in a wide range of habitats, from deserts to rainforests, though they do not seem able to survive in regions where temperatures below freezing persist for several months at a time. Some species, such as Acropyga pallida and Acropyga silvestrii for example, are found within a very wide range of habitats. Undoubtedly, the Acropyga lifestyle of existing below the surface buffers them against extremes of the outside environment.
Acropyga nests are found in leaf litter, under stones, in rotten wood (lying on or near the soil surface) and in the soil. Observations of nests of various species show the nests are large, consisting of at least several thousand individuals. The nest structure is diffuse with apparently no central nesting location (LaPolla et al., 2002). Tunnels and indistinct chambers stretch out over large areas through the nesting medium. Polygyny has been suggested for several species. The origins of polygyny remains uncertain, but two routes are suggested based on field observations. Biinzli (1935) found both the occurrence of pleometrosis (founding of a colony by multiple queens) and the acquisition of young queens by established colonies in Acropyga exsanguis.
All Acropyga are thought to be hypogaeic (living entirely underground), surviving primarily by "tending" mealybugs (Hemiptera: Pseudococcidae) on underground roots for their exudate (sometimes referred to as "honeydew") (Weber, 1944; Williams, 1998). This mutually beneficial relationship is called trophobiosis (Holldobler and Wilson, 1990).
Acropyga species are all believed to be obligate coccidophiles (dependent on their tended mealybugs for survival). The strength of this trophophitic relationship is clarified by a number of observations. Queens of eleven species have been observed emerging from their nests prior to their mating flight with a mealybug held in their mandibles (Biinzli, 1935; Wheeler, 1935b; Brown, 1945; Eberhard, 1978; Prins, 1982; Buschinger et al., 1987; Williams, 1998; Johnson et al., 2001). The mealybug that each queen carries presumably serves as a "seed individual" from which a new generation of mealybugs will be started in the newly founded ant colony (Weber, 1944; Williams, 1998). This behavior is called trophophoresy (LaPolla et al. 2002) with queens exhibiting this behavior said to be trophophoretic. The mealybugs utilized by Acropyga belong to the subfamily Rhizoecinae, and it is likely that the mealybugs are not able to survive independently of the ants (Williams, 1998). LaPolla et al. (2002) observed that Acropyga epedana keeps mealybugs with their brood. When a nest in captivity was starved, workers refused a variety of food items presented to them, suggestiving that the ants are completely dependent on the mealybugs as a food source. Fossil evidence suggests that the trophobiotic behavior ofAcropyga ants is an ancient one. Johnson et al. (2001) reported that Acropyga queens were discovered in Dominican amber, either holding a mealybug or with a mealybug nearby in the amber matrix. The amber was dated to the Miocene and is at least 15-20 million years old.
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.
- silvestrii. Acropyga silvestrii Emery, 1915g: 21, fig. 11 (w.) ETHIOPIA. Combination in Acropyga (Malacomyrma): Emery, 1922d: 109. See also: LaPolla, 2004a: 78.
Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.
LaPolla (2004) - (n= 10): TL: 1.16-2.15; HW: 0.383-0.454; HL: 0.429-0.506; SL: 0.297- 0.349; ML: 0.425-0.567; GL: 0.64-1.16; CI: 84.0-95.18; SI: 72.12-82.2.
Head: yellow to slightly brownish yellow; covered in dense layer of appressed hairs; head distinctly longer than broad; posterior margin entire; 11-10 segmented, incrassate antennae; apical segment about as long as proceeding 3 segments; scape fails to reach posterior margin by about length of pedicel; clypeus medially slightly convex, with several erect hairs; mandible with 4-7 uneven teeth; inner mandibular margin nearly parallel with anterior clypeal margin. Mesosoma: yellow; pronotum in lateral with a short shelf, then rising steeply toward mesonotum; mesonotum flat, covered in layer of appressed to suberect hairs; metanotal area often distinct; propodeum at about same height as mesonotum, rounded toward a steep declivity. Gaster: petiole thick and erect, rounded at apex; gaster yellow; covered in a thick layer of appressed hairs, with suberect to erect hairs scattered throughout.
LaPolla (2004) - Acropyga silvestrii Emery, 1915: 21. 5 syntype workers, ERITREA: Ghinda (Musee d'Histoire Naturelle Genève) [1 worker examined]. The designated lectotype is a worker labeled JSL TYPE # 125 and is deposited at MHNG.
- Biinzli, G.H. 1935. Untersuchungen iiber coccidophile Ameisen aus den Kaffeefelden von Surinam. Mitteilungen der Schweizerischen Entomologischen Gesellschaft 16:455-593.
- Brown, W.L., Jr. 1945. An unusual behavior pattern observed in a Szechuanese ant. Journal of the West China Border Research Society 15:185-186.
- Buschinger, J., J. Heinze & K. Jessen. 1987. First European record of a queen ant carrying a mealybug during her mating flight. NatUlwissenschaften 74:139-140.
- Eberhard, W.G. 1978. Mating swarms of a South American Acropygia [sic.] (Hymenoptera: Formicidae). Entomological News 89(1 & 2):14-16.
- Eisner, T. 1957. A comparative morphological study of the proventriculus of ants (Hymenoptera: Formicidae). Bulletin ofthe Museum of Comparative Zoology 116:439-490.
- Emery, C. 1915e. Formiche raccolte nell'Eritrea dal Prof. F. Silvestri. Boll. Lab. Zool. Gen. Agrar. R. Sc. Super. Agric. 10: 3-26 (page 21, fig. 11 worker described)
- Emery, C. 1922c. Hymenoptera. Fam. Formicidae. Subfam. Myrmicinae. [part]. Genera Insectorum 174B: 95-206 (page 109, Combination in Acropyga (Malacomyrma))
- Holldobler B . & E.O. Wilson. 1990. The Ants. Belknap Press, Cambridge, Massachusetts, 732 pp.
- Johnson, c., D. Agosti, J.H. Delabie, K. Dumpert, OJ. Williams, M. von Tschimhaus & U. Maschwitz. 2001 . Acropyga and Azteca Ants with Scale Insects: 20 Million Years ofIntimate Symbiosis. American Museum Noviates 3335:1-18.
- LaPolla, J.S. 2004a. Acropyga of the world. Contributions of the American Entomological Institute. 33(3):1-130. PDF (page 78, fig. 32C, worker described)
- LaPolla, J.S., S.P. Cover & U.G. Mueller. 2002. Natural history of the mealybug-tending ant Acropyga epedana, with descriptions of the male and queen castes. Transactions of the American Entomological Society 128(3):367-376.
- Prins, AJ. 1982. Review of Anoplolepis with reference to male genitalia, and notes on Acropyga. Annals of the South African Museum 89:215-247.
- Weber, N.A. 1944. The Neotropical coccid-tending ants of the genus Acropyga Roger. Annals of the Entomological Society of America 37:89-122.
- Wheeler, G.C. & J.C. Wheeler. 1953. The ant larvae of the subfamily Formicinae. Annals of the Entomological Society of America 46:126-171.
- Wheeler, W. M. 1927h. Ants collected by Professor F. Silvestri in Indochina. Boll. Lab. Zool. Gen. Agrar. R. Sc. Super. Agric. 20: 83-106 (page 100, fig. 7 worker described)
- Wheeler, W. M. 1935c. Myrmecological notes. Psyche (Camb.) 42: 68-72 (page 72, replacement name: indosinensis)
- Wheeler, W.M. 1935b. Ants of the genus Acropyga Roger, with description of a new species. Journal of the New York Entomological Society 43:321-329.
- Williams, D J . 1998. Mealybugs of the genera Eumyrmococcus Silvestri and Xenococcus Silvestri associated with the ant genus Acropyga Roger and a review of the subfamily (Hemiptera, Coccoidea, Pseudoccidae). Bulletin of the British Museum (Natural History)(Entomology) 67:1-64.