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Pseudomyrmex gracilis (Fabricius) 1804
"graceful twig ant", "elongate twig ant", or "Mexican twig ant"

by Joe A. Macgown, uploaded on 23 July 2009, updated on 25 November 2013

Pseudomyrmex gracilis, side view of a worker
(Photo by Joe A. MacGown)

Pseudomyrmex gracilis, side view of a worker
(Photo by Joe A. MacGown)

Most of the species in the genus Pseudomyrmex make their nest in dead twigs or stems of woody plants, hollow stems of grasses, and various other natural or manmade cavities. A few of these species are uniquely adapted for living in live plant domatia, with the swollen-thorn acacias being a good example of this. This genus is distinctive and can easily be distinguished from other US genera by the following characteristics: body elongate with postpetiole; eyes extremely large, more than 1.5 times as long as wide; antennal scapes short; 12-merous antenna; relatively short mandibles with 7-10 teeth; sting present.

Pseudomyrmex gracilis is large orange, black, to bicolored orange and black species thought to be native to Mexico, but also found from Argentina and Brazil through Texas, parts of southeastern US, and the Caribbean. Its status as an invasive species in the US is unclear, but due to its apparent spread in the US and its painful sting, this species is worth monitoring.

Taxonomic History (provided by Barry Bolton, 2013)
Formica gracilis Fabricius (1804); Combination in Leptalea: Erichson (1839); in Pseudomyrma, Roger, (1862); in Pseudomyrmex (Clavanoda), Enzmann (1944); in Pseudomyrmex, Kusnezov (1953). Senior synonym of Pseudomyrmex longinoda, Brown (1949); of Pseudomyrmex variabilis, Ward (1989); of Pseudomyrmex bicolorPseudomyrmex canescensPseudomyrmex dimidiata, Pseudomyrmex glabriventrisPseudomyrmex mexicanaPseudomyrmex pilosulaPseudomyrmex sericata, Pseudomyrmex velifera,Pseudomyrmex volatilis and material of the unavailable name Pseudomyrmex guayaquilensis referred here, Ward (1993); of Pseudomyrmex atrinoda, Wild (2007).

Workers of the graceful twig ant is easily recognized by its elongate, wasp-like appearance, large size (TL 8-10 mm, HW 1.39-2.07), orange and black to entirely blackish or entirely organgish-brown coloration, large eyes (REL 0.54–0.60) ocelli, elongate two-segmented waist, and a well developed sting. Mandible with 7 -10 teeth. Body with numerous fine, silvery-white setae.

Biology and Economic Importance
Similar to other Pseudomyrmex species, P. gracilis nests in hollow twigs, branches, stems, and grasses, but also in in crevices in buildings (Wetterer 2010). Klotz et al. (1995) reported finding nests of this species in wooden door frames of houses. Colony size is typically small with one queen per colony.

According to Ward (1993), P. gracilis may be found in a wide variety of habitats such as mangrove forests, thorn scrub, and rainforests. However, it may also be common in disturbed habitats such as old fields, roadsides, and secondary forest. In Central America (Mexico to Panama), this species has been reported to occupy swollen-thorn acacias.

Pseudomyrmex gracilis workers and queens may inflict painful stings. Stings usually occur after a worker falls from foliage onto human skin, but also when workers are defending their colony. According to Wheeler and Wheeler (1956), P. gracilis readily defends it host plant or colony by swarming and stinging intruders.

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.

US Distribution: AL, FL, GA, HA, LA, MS, SC, and TX (MEM records; Wetterer 2010; Doug Booher, Pers. Comm).

Literature Cited
Bolton, B. 2013.  Bolton World Catalog Ants. Available online: Accessed 25 Novemberl 2013.

Erichson, W. F. 1839. Bericht über die Leistungen im Gebiete der Naturgeschichte während des Jahres 1838. IX. Insecten. Archiv für Naturgeschichte 5(2): 281-375.

Enzmann, E. V. 1944. Systematic notes on the genus Pseudomyrma. Psyche (Cambridge) 51: 59-103.

Fabricius, J. C. 1804. Systema Piezatorum secundum ordines, genera, species, adjectis synonymis, locis, observationibus, descriptionibus. Brunswick: C. Reichard, xiv + 15-439 + 30 pp.

Kempf, W. W. 1961. Estudos sôbre Pseudomyrmex. III. (Hymenoptera: Formicidae). Studia Entomologica 4: 369-408. 

Kusnezov, N. 1953. La fauna mirmecológica de Bolivia. Folia Universitaria. Cochabamba 6: 211-229. 

Roger, J. 1862c Synonymische Bemerkungen. 1. Ueber Formiciden. Berliner Entomologische Zeitschrift 6: 283-297. 

Ward, P. S. 1989. Systematic studies on pseudomyrmecine ants: revision of the Pseudomyrmex oculatus and P. subtilissimus species groups, with taxonomic comments on other species. Quaestiones Entomologicae 25: 393-468.

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

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

Wild, A. L. 2007. A catalogue of the ants of Paraguay (Hymenoptera: Formicidae). Zootaxa 1622: 1-55.


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