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Species: Pseudomyrmex gracilis   (Fabricius, 1804) 

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See Also:

Pseudomyrmex gracilis_cf, Pseudomyrmex gracilis_nr, Pseudomyrmex gracilis argentinus

Taxonomic History (provided by Barry Bolton, 2020)

Extant: 1 valid subspecies

Formica gracilis Fabricius, 1804 PDF: 405 (w.) CENTRAL AMERICA. Neotropic. AntCat AntWiki HOL

Taxonomic history

Combination in Leptalea: Erichson, 1839 PDF: 309; in Pseudomyrma: Roger, 1862c PDF: 289; in Pseudomyrmex (Clavanoda): Enzmann, 1944 PDF: 61; in Pseudomyrmex: Kusnezov, 1953f PDF: 214.
Senior synonym of Pseudomyrmex longinoda: Brown, 1949a PDF: 43; Kempf, 1961a PDF: 370; of Pseudomyrmex variabilis: Ward, 1989a PDF: 439; of Pseudomyrmex bicolor, Pseudomyrmex canescens, Pseudomyrmex dimidiata, Pseudomyrmex glabriventris, Pseudomyrmex mexicana, Pseudomyrmex pilosula, Pseudomyrmex sericata, Pseudomyrmex velifera, Pseudomyrmex volatilis and material of the unavailable name Pseudomyrmex guayaquilensis referred here: Ward, 1993 PDF: 155; of Pseudomyrmex atrinoda: Wild, 2007B PDF: 55.
See also: Ward, 1999B PDF: 521.
Current subspecies: nominal plus Pseudomyrmex gracilis argentinus.


  Geographic regions (According to curated Geolocale/Taxon lists):
    Americas: Argentina, Barbados, Belize, Bolivia, Brazil, Colombia, Costa Rica, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Honduras, Jamaica, Mexico, Nicaragua, Panama, Paraguay, Peru, Trinidad and Tobago, United States, Uruguay, Venezuela
    Oceania: Hawaii
  Biogeographic regions (According to curated Bioregion/Taxon lists):
    Nearctic, Neotropical, Oceania
  Native to (according to species list records):
    Nearctic, Neotropical bioregions

Distribution Notes:

Pseudomyrmex gracilis is a widespread New World species, ranging from southern United States to Argentina and Uruguay. It is present as an introduced species in Hawaii and Florida.


Befitting its wide distribution and variable phenotype, P. gracilis can be found in a variety of habitats from mangroves and thorn scrub to rainforest. It is often particularly common in disturbed situations such as old fields, roadsides, and secondary forest. Nests are usually located in dead twigs or small branches, belonging to a great variety of woody plants. In Central America (Mexico to Panama) there are a substantial number of records of colonies occupying swollen-thorn acacias. In a few localities P. gracilis is a common acacia inhabitant and under these circumstances it may exhibit local adaptation and phenotypic differentiation (Ward, 1993).


  • masticatory margin of mandible with 7-10 teeth
  • median clypeal lobe laterally rounded
  • eyes large and elongate (REL2 0.54-0.60)
  • pronotum dorsolaterally submarginate
  • petiole long and slender (PLI 0.46-0.57) with a well developed anterior peduncle
  • head and mesosoma densely and finely punctulate-coriarious to coriarious-imbricate, subopaque to sublucid (not matte) in appearance
  • standing pilosity abundant, fine, predominantly pale silvery-white (not black), common on mesosoma dorsum and on external faces of tibiae
  • size and color extremely variable (HW 1.39-2.07), varying from unicolorous black (appendages lighter) to unicolorous orange-brown, with many intermediate and bicoloured combinations

Taxonomic Notes:

Pseudomyrmex gracilis presents one of the more taxonomically challenging problems in the genus Pseudomyrmex. The concept of P. gracilis adopted here encompasses an impressive amount of phenotypic variability. Collections from single regions often give the impression that this variation is distributed bimodally or multimodally, as more or less discrete morphs. For example, nest samples from Costa Rica can be segregated on the basis of worker morphology into (i) a large (HW > 1.80), usually lighter-colored form (with orange mesosoma, petiole, and postpetiole, and black head and gaster), (ii) a smaller, bicolored, usually more heavily infuscated form, and (iii) an all-black form of variable size. The first two are typically found in open or xeric habitats while the third is more common in closed forest, suggesting some ecotypic differentiation. Yet when large enough sample sizes are obtained all degrees of intermediacy in size and color are encountered, and the variation in color (less so size) can be seen among individuals (workers and alate queens) from the same nest. Thus, if there are ecotypes they do not appear to be reproductively isolated.


(Dutch vernacular name: zwarte acaciamier)


Beardsley, J. W. 1979. Notes on Pseudomyrmex gracilis mexicanus (Roger). Proceedings of the Hawaiian Entomological Society 23: 23.

Ward, P. S. 1985. The Nearctic species of the genus Pseudomyrmex (Hymenoptera: Formicidae). Quaestiones Entomologicae 21: 209-246.

Ward, P. S. 1993. Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae). Journal of Hymenoptera Research 2: 117-168.

Ward, P. S. 1999. Systematics, biogeography and host plant associations of the Pseudomyrmex viduus group (Hymenoptera: Formicidae), Triplaris- and Tachigali-inhabiting ants. Zoological Journal of the Linnean Society 126: 451-540.

Wetterer, J. K. 2010. Worldwide spread of the graceful twig ant, Pseudomyrmex gracilis (Hymenoptera: Formicidae). Florida Entomologist 93: 535-540.

Taxonomic Treatment (provided by Plazi)

Scientific Name Status Publication Pages ModsID GoogleMaps
Pseudomyrmex gracilis   Wild, A. L., 2007, A catalogue of the ants of Paraguay (Hymenoptera: Formicidae)., Zootaxa 1622, pp. 1-55: 40, (download) 40 21367
Pseudomyrmex gracilis   Wild, A. L., 2007, A catalogue of the ants of Paraguay (Hymenoptera: Formicidae)., Zootaxa 1622, pp. 1-55: 55, (download) 55 21367

Specimen Habitat Summary

Found most commonly in these habitats: 62 times found in tropical dry forest, 41 times found in edge of second-growth rainforest, 39 times found in rainforest edge, 41 times found in montane wet forest, 33 times found in rainforest, 31 times found in roadside vegetation, 21 times found in roadside, 26 times found in roadside edge, 14 times found in 2º lowland rainforest, 26 times found in tropical moist forest, ...

Found most commonly in these microhabitats: 135 times on low vegetation, 76 times ex dead twig, 33 times beating vegetation, 19 times Malaise trap, 10 times ex dead twig of Gliricidia sepium, 7 times ex dead twig of vine, 10 times on tree trunk, 9 times ex dead weed stalk, 12 times nest in twig above ground, 12 times strays, 7 times ex swollen-thorn Acacia, ...

Collected most commonly using these methods: 58 times Fogging, 64 times Malaise, 50 times search, 39 times Beating, 28 times Malaise trap, 34 times canopy fogging, 29 times direct collection, 12 times hand collecting, 12 times sweeping, 9 times blacklight trap, 9 times beating vegetation (1 hour), ...

Elevations: collected from 1 - 2480 meters, 352 meters average

Type specimens: Holotype of Pseudomyrma canescens: casent0902843; Holotype of Pseudomyrma volatilis: casent0902846; Holotype of Pseudomyrms sericata: casent0902845; Lectotype of Pseudomyrma pilosula: casent0902844; Lectotype of Pseudomyrma variabilis: casent0902842; syntype of Pseudomyrma gracilis atrinoda: casent0915509; syntype of Pseudomyrma gracilis glabriventris: casent0915507; syntype of Pseudomyrma gracilis mexicana guayaquilensis: casent0907478; type of Pseudomyrma bicolor: focol0524

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