Subfamily FORMICINAE
Tribe PLAGIOLEPIDINI
Brachymyrmex depilis Emery

by Joe A. MacGown, uploaded 3 November 2009, last updated on 4 September 2026

Brachymyrmex depilis, frontal view of head of a worker (photo by Joe A. MacGown)

Brachymyrmex depilis, full face view of the head of a worker (Photo by James Lewis and Joe A. MacGown)

Brachymyrmex depilis, lateral view of the head of a worker (Photo by James Lewis and Joe A. MacGown)

Brachymyrmex depilis, dorsal view of the head of a worker (Photo by James Lewis and Joe A. MacGown)

Brachymyrmex depilis, full face view of the head of a queen (Photo by James Lewis and Joe A. MacGown)

Brachymyrmex depilis, lateral view of the head of a queen (Photo by James Lewis and Joe A. MacGown)

Brachymyrmex depilis, dorsal view of the head of a queen (Photo by James Lewis and Joe A. MacGown)

Brachymyrmex depilis, full face view of the head of a male (MS, Pontotoc Co.) (Photo by Joe A. MacGown)

Brachymyrmex depilis, lateral view of the head of a male (MS, Pontotoc Co.) (Photo by Joe A. MacGown)

Brachymyrmex depilis, dorsal view of the head of a male (MS, Pontotoc Co.) (Photo by Joe A. MacGown)

Introduction
Brachymyrmex is a New World genus whose members are minute, soft-bodied, have a small petiolar scale, and a nine segmented antenna without a club. Workers have well developed eyes. Color ranges from pale light-yellow to dark brown. Species is this genus usually nest in soil or rotting wood. This group is in drastic need of revision.

Taxonomic History (provided by Barry Bolton, 2013)
Brachymyrmex heeri subsp. depilis Emery, 1893: 635 (w.q.) U.S.A. Nearctic. Wheeler & Wheeler, 1953: 139 (l.). Raised to species: Santschi, 1923: 663. Senior synonym of Brachymyrmex nanellus: Creighton, 1950: 359; of Brachymyrmex flavescens: Cole, 1953: 266.

Diagnosis. Worker: Minute (TL ≈ 1.3–1.5 mm), soft bodied; entire body light yellow to yellowish brown with antennae and legs a paler lighter yellow; lacking obvious sculpture, body shiny beneath pubescence; erect setae limited to anterior region of head including clypeus and gaster; entire body with dense, short, appressed pubescence. Head slightly longer than wide, slightly concave posteriorly; mandibles triangular with five teeth, apical tooth the longest with second and fourth teeth bigger than the third and basal teeth; frontal carina slightly expanded, partially covering antennal bases; antenna with nine antennomeres with apical antennomere about twice as long as others; scape barely surpassing posterior margin of head; eyes large with 16 to 20 facets; ocelli lacking. In lateral mesosoma not entire, promesonotal suture distinct; propodeum lacking spines or other adornment, declivity approximately 45°. Waist with a single petiole, node low and directed anteriorly, rounded ventrally, mostly hidden from view from overhanging gaster.  Gaster lacking a sting, acidopore present and with fringe of short setae.

Queen: Similar to workers but larger (TL ≈ 3.5–4.0 mm); yellowish brown; lacking obvious sculpture; scattered short erect setae on head, mesosomal dorsum, and gaster; entire body with dense, short, appressed pubescence, pubescence longer than in worker, obscuring shininess of integument. Head as wide to slightly wider than long, posterior margin concave; mandibles similar to workers; nine antennomeres, scape surpasses posterior margin of head by about the width of scape; funiculus similar to worker; eyes enlarged, located on sides of head near middle; three ocelli present. Mesosoma entire, elongate rounded rectangular, dorsum flattened with wings or wing scars. Wings if present transparent, stigma present; forewing with costal, basal, subbasal, and submarginal cells. Waist similar to worker. Acidopore present.

Male: Minute (TL ≈ 1.5 mm); head and body orangish brown, mesosoma with infuscation; body mostly shiny, lacking sculpture; erect setae lacking except for a few on gaster, especially posteriorly; fine, short appressed pubescence on head, mesosomal dorsum, and gaster that does not obscure the shininess of the integument. Head about as wide as long, posterior margin straight; mandibles reduced, thin, lacking dentition; ten antennomeres; scape long, surpassing posterior margin of the head; eyes greatly enlarged, over half the length of the head; three ocelli present. Mesosoma expanded, rounded square in shape, mesoscutellum overhanging propodeum; propodeum lacking adornment, declivity steep. Wings transparent, similar to queen. Waist with single segment, petiole with erect node, slender, rounded triangular in profile, not overhung by gaster. Gastral segments following the first two shorter in lateral view and gradually curling ventrally toward anterior region giving a slightly scooped appearance; parameres rounded triangular with setae on margins.

Similar species. Brachymyrmex depilis is distinguished from other species in the group in this region by its lack of erect hairs (only a few on the edges of the gastral tergites) and relatively large eye. An undescribed species known only from FL is similar in that it lacks erect hairs, but the eye is much smaller with only 3-4 facets in the greatest diameter of the eye. Other yellow species known from the U.S., including a new species that has been collected from southern AL and MS, differ in that they have semi-erect hairs present on the promesonotum. Other species of Brachymyrmex known from this region are dark brown. The invasive B. patagonicus is easily separated by its dark brown color, a few stiff erect setae on mesosomal dorsum, and sparse pubescence. This invasive species is rapidly spreading throughout the southern USA.

Biology and Economic Importance
This species is common in the Southeast in certain forested habitats, especially mixed forests with at least some terrain. However, it appears to be lacking in flatwoods areas, Black Belt Prairie remnants, and fields. Alates have been collected in mid to late June. This species is not a pest species.

Distribution
Range United States, S Canada, Mexico. Most U.S. states and south into Mexico. This species is putatively wide ranging. A badly needed taxonomic revision of the North America forms will likely reveal Brachymyrmex depilis is a number of distinctive species (Anonymous. 2015). In the southeastern US, this is a common species in rich forests founnd in AL, AR, FL, GA, LA, MS, NC, SC, and TN.

Literature Cited
Anonymous. 2015. Antwiki: Brachymyrmex depilis. Online at: http://www.antwiki.org/wiki/Brachymyrmex_depilis. Accessed 14 July 2015.

Creighton, W. S. 1950. The ants of North America. Bulletin of the Museum of Comparative Zoology 104:1-585.

Cole, A. C., Jr. 1953g. Studies of New Mexico ants. V. The genus Pheidole with synonymy (Hymenoptera: Formicidae). Journal of the Tennessee Academy of Science 28:297-299.

Emery, C. 189. Beiträge zur Kenntniss der nordamerikanischen Ameisenfauna. Zoologische Jahrbücher. Abteilung für Systematik, Geographie und Biologie der Tiere 7:633-682.

Santschi, F. 1923. Revue des fourmis du genre Brachymyrmex Mayr. Anales del Museo Nacional de Historia Natural de Buenos Aires 31:650-678.

Wheeler, G. C.; Wheeler, J. 1953. The ant larvae of the subfamily Formicinae. Annals of the Entomological Society of America 46:126-171.

Links
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Antwiki