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Species: Pseudomyrmex gracilis   (Fabricius, 1804) 

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See Also:

Pseudomyrmex gracilis_cf, Pseudomyrmex gracilis argentinus, Pseudomyrmex gracilis atrinoda, Pseudomyrmex gracilis bicolor, Pseudomyrmex gracilis carapuna, Pseudomyrmex gracilis glabriventris, Pseudomyrmex gracilis guayaquilensis, Pseudomyrmex gracilis longinoda, Pseudomyrmex gracilis peruviana, Pseudomyrmex gracilis velifera

Taxonomic History (provided by Barry Bolton, 2015)

2 subspecies

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

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.
Current subspecies: nominal plus Pseudomyrmex gracilis argentinus.
See also: Ward, 1999B PDF: 521.


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)

Wild, A. L., 2007:
Alto Paraguay/ Boquerón , Alto Paraná , Amambay, Caaguazú , Canindeyú , Central, Concepcion, Cordillera, Guairá , Itapúa , Misiones, Ñeembucú , Paraguarí , San Pedro, “Paraguay” (s. loc.) (ALWC, BMNH, IFML, INBP, MCSN, MCZC, MZSP, NHMB, PSWC). Literature records: Caaguazú , Central, Cordillera, “Paraguay”(s. loc.) (Emery 1890b, Emery 1896b, Forel 1907d, Forel 1908b, Forel 1909, Fowler 1981, Santschi 1916, Santschi 1934 [as “ atrinodis ”]).
Formica gracilis Fabricius 1804: 405.
Leptalea gracilis (Fabricius) . Erichson 1839: 309.
Pseudomyrma gracilis (Fabricius) . Roger 1862b: 289.
Pseudomyrma (Clavanoda) gracilis (Fabricius) . Enzmann 1944: 61.
Pseudomyrma gracilis var. atrinoda Santschi 1934: 26. NEW SYNONYMY . [ holotype w examined, NHMB ; Rio Negro , Paraná , Brazil ( Reichensperger )] .
Pseudomyrmex gracilis (Fabricius) . Kusnezov 1953: 214.
Pseudomyrmex gracilis var. atrinoda (Santschi) . Kempf 1958: 434.
Pseudomyrmex gracilis var. atrinodus (Santschi) . Kempf 1972: 219.
Ants in the Pseudomyrmex gracilis species complex are ubiquitous in the neotropics, and the species P. gracilis itself presents a confusing array of variation (Ward 1989). Santschi distinguished his variety P. atrinodus on the basis of small size and light coloration on parts of the mesosoma, but I have examined the type material and in both these characters P. atrinodus is well within the normal range of variation of the species. Phil Ward, who is revising Pseudomyrmex , concurs with this synonymy (Ward, pers comm.)

Specimen Habitat Summary

Found most commonly in these habitats: 41 times found in montane wet forest, 14 times found in 2º lowland rainforest, 21 times found in tropical dry forest, 10 times found in tropical moist forest, 9 times found in tropical wet forest, 3 times found in SSO 350m, 8 times found in mangrove, 6 times found in La Selva, 8 times found in lowland rainforest, 2 times found in wet broadleaf forest, ...

Collected most commonly using these methods or in the following microhabitats: 58 times Fogging, 59 times Malaise, 46 times search, 29 times Beating, 20 times ex dead twig, 8 times hand collecting, 8 times ex dead Acacia, 8 times Foggin, 4 times Sweeping, 1 times Dead branch, 2 times sweep net, ...

Elevations: collected from 1 - 1676 meters, 276 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

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