Forelius pruinosus

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Forelius pruinosus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Dolichoderinae
Tribe: Leptomyrmecini
Genus: Forelius
Species: F. pruinosus
Binomial name
Forelius pruinosus
(Roger, 1863)

Forelius pruinosus casent0005320 profile 1.jpg

Forelius pruinosus casent0005320 dorsal 1.jpg

Specimen labels


Colonies typically inhabit large polygnynous ground nests. Disorganized small soil craters may also be found at the entrance to some uncovered ground nest entrances. Their predilection for open habitats leads to Forelius pruinosus being a common ant in many anthropogenic and disturbed habitats.

At a Glance • Polygynous  



Similar in form to Tapinoma but the small petiole, partially hidden by the gaster, is larger in comparison to the almost nonexistent petiolar node of Tapinoma.

Forelius from the western United States and northern Mexico are part of a species complex that is in need of taxonomic revision. The form we currently assign to Forelius pruinosus, at least in the southwest, likely includes pruinosus and one or more undescribed species. This species group can be distinguished from Forelius mccooki by a lack of standing hairs on the scape.

Ward (2005) provides his evaluation of the western North American Forelius species: After examining a large series of Forelius from the United States and northern Mexico I can find no consistent difference in worker head shape: the posterior margin of the head varies continuously from weakly convex through straight to weakly concave. Color is also variable, ranging from dark brown to yellowish-orange. Some nest series contain both light and dark-colored workers. It is possible that the California populations are not conspecific with F. pruinosus (described from Cuba), but these and other western samples seem to grade insensibly into material from farther east and south, including populations in Florida and the West Indies with consistently dark and densely pubescent workers, which correspond to 'F. pruinosus' (s.s.). The complex needs further study but because reliable diagnostic differences have not yet been uncovered I treat F. analis (type locality Chihuahua, Mexico) as a junior synonym of F. pruinosus (syn. nov.).

Identification Keys including this Taxon


Distribution based on Regional Taxon Lists

Nearctic Region: United States.
Neotropical Region: Cuba (type locality), Mexico.
Range United States, Mexico, Caribbean and possibly South America. Described from Cuban specimens, the species as currently understood occurs in portions of the northern United States (records exist as far north as Long Island and North Dakota), throughout the southern United States, Cuba, Mexico and possible into South America.

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb


Forelius pruinosus, senso lato, is an arid, open habitat ant that thrives in hot and dry conditions. Forelius species in the southwestern U.S. are active in the hottest part of the day, foraging and running along trails at temperatures that other co-occurring species cannot tolerate. Foraging does not take place at night, presumably because of cooler temperatures. Trunk trails are used by foragers with workers searching for food on the ground and on vegetation. Foragers are general scavengers that will tend aphids and feed from plant nectaries.

M.R. Smith (1965), reporting on eastern U.S. ant pests, provides this description of their biology: The ants seem to prefer open habitats such as fields, meadows, pastures, and entirely bare areas, and will also nest in open woods out of dense and prolonged shade. Nests are constructed in exposed soil or soil under the cover of stones, other objects, and under the bark of logs and stumps. Entrance holes of nests in the soil commonly have crater-shaped mounds of earth surrounding them, but the craters may be imperfectly shaped, or the ground may be more or less bare. Colonies are small to moderate-sized. Males and winged females have been observed in Florida from May into July. Workers are very fond of honeydew, and tend honeydew-excreting insects; they also live on both live and dead insects. The very agile, fast-moving workers form pronounced foraging trails. M. S. Blum, in a letter to the author, wrote that the ants lay down on their foraging trails a methyl-n-amyl ketone substance, which is emitted from the gaster. Workers have been induced to follow artificial trails on which this synthetic chemical has been placed. The odor emitted by live or freshly killed workers has been likened to that of rotton coconuts and is similar to the odor of ants of the genus Tapinoma.

This species is a house pest particularly in the Gulf Coast States. Most frequently the ants invade houses from outdoors, but it is quite likely that they may nest within houses as well. Although workers feed on most of the foods commonly eaten by ants, they seem to show a preference for sweets.

Some of this account is curious, as the species is not known to be much of a house pest today. The reported nesting locations under wood or stones is also interesting. Most of the forms of this ant do not prefer such microsites.

Roeder et al. (2018) in an Oklahoma study found the CTmax (critical thermal maximum) for this species was 56.0 ± 0.3 C and the average worker mass was 0.099 ± 0.004 mg.

Regional Notes

New Mexico

Mackay and Mackay (2002) - Habitat Widely distributed in many habitats in New Mexico. Most common in arid habitats (desert scrub, including open weedy areas, grama grasslands, fluff grass areas, creosote scrub, mesquite woodlands), although also occurs in Juniper, sagebrush, riparian and even into pine forests. Biology This ant usually nests in the soil, in open areas, but may be found nesting under stones. The nest usually consists of a small mound (diameter of few cms) with the entrance hole in the center. Reproductives were found in nests from May to August. Multiple queens are present in nests. The habits are very similar to those of Forelius mccooki. Food consists of living and dead insects; this species also tends Homoptera and feeds on flower nectar. It can be a serious house pest.

Association with Other Organisms

This species is a host for the Microdon fly Microdon fuscipennis (a predator) in Georgia (Macquart, 1834).






The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • pruinosus. Tapinoma pruinosum Roger, 1863a: 165 (w.) CUBA. Wheeler, G.C. & Wheeler, J. 1951: 185 (l.). Combination in Iridomyrmex: Wheeler, W.M. 1913b: 497; in Forelius: Wheeler, G.C. & Wheeler, J. 1986g: 13; Shattuck, 1992c: 95. Senior synonym of testaceus: Cuezzo, 2000: 261; of analis: Ward, 2005: 9. See also: Creighton, 1950a: 342; Petralia & Vinson, 1980: 386; Guerrero & Fernández, 2008: 57.
  • analis. Tapinoma anale André, 1893b: 148 (w.) MEXICO. Combination in Iridomyrmex: Forel, 1908b: 62; in Forelius: Wheeler, G.C. & Wheeler, J. 1986g: 13. Subspecies of pruinosus: Emery, 1895c: 333; Wheeler, W.M. 1913b: 497; Creighton, 1950a: 343; Shattuck, 1994: 96. Junior synonym of pruinosus: Wheeler, G.C. & Wheeler, J. 1986g: 13; Bolton, 1995b: 190. Status as species: Forel, 1908b: 62; Emery, 1913a: 26; Cuezzo, 2000: 222. Junior synonym of pruinosus: Ward, 2005: 9.
  • testaceus. Iridomyrmex pruinosus var. testaceus Cole, 1936b: 121 (w.q.) U.S.A. Junior synonym of analis: Creighton, 1950a: 343; of pruinosus: Cuezzo, 2000: 261.



Descriptive. pruinosus translates to "covered with hoarfrost" and this presumably describes the dense pubescence that covers the workers


  • André, E. 1893b. Description de quatre espèces nouvelles de fourmis d'Amérique. Rev. Entomol. (Caen) 12: 148-152 PDF
  • Creighton, W. S. 1950a. The ants of North America. Bull. Mus. Comp. Zool. 104: 1-585 (page 342, see also)
  • Cuezzo, F. 2000. Revisión del género Forelius (Hymenoptera: Formicidae: Dolichoderinae). Sociobiology 35: 197-275 (page 261, Senior synonym of testaceus)
  • Mackay, W. P. and E. Mackay. 2002. The ants of New Mexico (Hymenoptera: Formicidae). Edwin Mellen Press, Lewiston, NY.
  • Petralia, R. S.; Vinson, S. B. 1980 [1979]. Comparative anatomy of the ventral region of ant larvae, and its relation to feeding behavior. Psyche (Camb.) 86: 375-394 (page 386, see also)
  • Roeder, K. A., D. V. Roeder, and M. Kaspari. 2018. The role of temperature in competition and persistence of an invaded ant assemblage. Ecological Entomology. 43:774-781. doi:10.1111/een.12663
  • Roger, J. 1863a. Die neu aufgeführten Gattungen und Arten meines Formiciden-Verzeichnisses nebst Ergänzung einiger früher gegebenen Beschreibungen. Berl. Entomol. Z. 7: 131-214 (page 165, worker described)
  • Shattuck, S. O. 1992c. Generic revision of the ant subfamily Dolichoderinae (Hymenoptera: Formicidae). Sociobiology 21: 1-181 (page 95, Combination in Forelius)
  • Smith, M. R. 1965. House-infesting ants of the eastern United States. Their recognition, biology, and economic importance. United States Department of Agriculture, Technical Bulletin 1326
  • Ward, P.S. 2005. A synoptic review of the ants of California (Hymenoptera: Formicidae). Zootaxa 936: 1-68 (page 9, Senior synonym of analis)
  • Wheeler, G. C.; Wheeler, J. 1951. The ant larvae of the subfamily Dolichoderinae. Proc. Entomol. Soc. Wash. 53: 169-210 (page 185, larva described)
  • Wheeler, G. C.; Wheeler, J. 1986g. The ants of Nevada. Los Angeles: Natural History Museum of Los Angeles County, vii + 138 pp. (page 13, Combination in Forelius)
  • Wheeler, W. M. 1913b. The ants of Cuba. Bull. Mus. Comp. Zool. 54: 477-505 (page 497, Combination in Iridomyrmex)