Pheidole obscurithorax

Nomenclature

Species: Pheidole obscurithorax Naves, 1985

Usage: valid

External links

Diagnostic description

Diagnosis of worker among Antkey species

Worker castes bimorphic. Head shape ovoid (minor workers) or subrectangular with posterolateral lobes (majors), but never triangular. Antenna 12-segmented. Antennal club 3-segmented. Antennal insertions at least partly covered by frontal lobes; not surrounded by a raised sharp-edged ridge. Frontal lobes do not obscure face outline between mandible and eye; relatively close together so that the posteromedian portion of the clypeus, where it projects between the frontal lobes, is at most only slightly broader than one of the lobes. Posterolateral corners of head unarmed, without spines. Mandibles triangular. Mesosoma with erect hairs. Pronotal spines absent. Propodeum armed with spines or teeth. Slope of mesosoma steep. Waist 2-segmented. Petiole pedunculate with a distinct and upright node; lacking large subpetiolar process. Postpetiole attached to lower surface of gaster; not swollen; in dorsal view not distinctly broader than long or distinctly wider than petiole. Minor worker characters. Head ovoid; distinctly longer than wide; smooth and shining, lacking punctation. Antennal scrobe lacking. Posterior head margin strongly convex. Antennal scapes extend beyond posterior margin of head. Postpetiole not swollen relative to petiole. Lateral portions of petiole and postpetiole strongly punctate. Color brown or reddish brown to black. Major worker characters. Antennal scrobe absent, no depression capable of receiving antennal scapes visible. Posterolateral lobes distinctly rugose; rugae above eye level strongly reticulated.

Minor workers of P. obscurithorax are most easily distinguished from P. anastasii, P. bilimeki, P. flavens, P. moerens and P. punctatissima by the smooth and shining head. They are separated from those of P. megacephala by the postpetiole, which is not swollen in comparison to the petiole. The posterior head margin is strongly convex, compared to relatively flat in P. teneriffana and weakly convex in P. fervens. They are further separated from majors of these species by the stronger punctation on the lateral portions of the petiole and postpetiole, and also by the darker brown to black (versus yellowish brown) color.

The absence of an antennal scrobe and distinct frontal carinae distinguish P. obscurithorax from all other major workers of Pheidole introduced or commonly intercepted in the United States, with the exception of P. megacephala. Pheidole obscurithorax is easily separated from P. megacephala, however, by the very densely packed rugoreticulum of the posterolateral lobes (versus smooth and shining posterolateral lobes).

Distribution

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A South American native that has been introduced to the U.S. gulf coast. Photo by ©Alexander L. Wild, alexanderwild.com	A South American native that has been introduced to the U.S. gulf coast Photo by ©Alexander L. Wild, alexanderwild.com
The long, sharp jaws of this soldier indicate a predominately predatory species. Photo by ©Alexander L. Wild, alexanderwild.com	A major worker of the South American big-headed ant. Photo by ©Alexander L. Wild, alexanderwild.com
This species stays ahead of the competition using group retrieval of food items (in this case, a scavenged wasp carcass). Working together the ants can usually get the bounty home before a more aggressive species usurps their find. Photo by ©Alexander L. Wild, alexanderwild.com	Lateral view of body, entire, adult worker. Photo by April Nobile, Antweb.org.
Dorsal view of body, entire, adult worker. Photo by April Nobile, Antweb.org.	Anterior dorsal view of head, adult worker. Photo by April Nobile, Antweb.org.
Lateral view of body, entire, adult worker. Photo by April Nobile, Antweb.org.	Dorsal view of body, entire, adult worker. Photo by April Nobile, Antweb.org.
Anterior view of head, adult worker. Photo by April Nobile, Antweb.org.	Lateral view of body, entire, adult worker. Photo by April Nobile, Antweb.org.
Dorsal view of body, entire, adult worker. Photo by April Nobile, Antweb.org.	Anterior view of head, adult worker. Photo by April Nobile, Antweb.org.
Close-up view of head, adult worker. Abundant amount of reticulated rugae above eye level. Photo by April Nobile, Antweb.org, modified.	Anterior view of head, adult worker. Posterolateral lobes with longitudinal carinae frequently being intersected and interrupted by transverse carinae to form a dense mesh of rugoreticulation. This character, combined with the absence of antennal scrobes, is used to separate the major worker of Pheidole obscurithorax from that of Pheidole fervens and Pheidole teneriffana.
Anterior view of head, adult worker. The posterolateral lobes distinctly rugose and the lack of a punctate ground sculpture gives the head a shiny appearance. Used in Antkey to separate the major workers of Pheidole fervens, Pheidole flavens, Pheidole moerens, Pheidole obscurior and Pheidole teneriffana from those of all other Pheidole species.	Anterior view of head, adult worker. Posterior margin of head strongly convex.
Anterior view of head, adult worker. The posterior margin of the head is strongly convex and arching strongly towards the eyes. Used in Antkey to separate the minor worker of Pheidole obscurithorax from Pheidole teneriffana (flat margin) and Pheidole fervens (weakly convex).	Anterior view of head, adult worker. Antennal scrobe absent, no depression capable of receiving antennal scapes visible.
Anterior view of head, adult worker. Used to distinguish the major worker of Pheidole obscurithorax from that of Pheidole fervens, Pheidole flavens, Pheidole moerens and Pheidole teneriffana. The first species lacks any depression capable of receiving any portion of the antennae.	Lateral view of waist, adult worker. Petiole and postpetiole strongly sculptured laterally. Photo by April Nobile, Antweb.org, modified.
Lateral view of waist, adult worker. The postpetiole of the major and minor worker is not distinctly larger in volume than the petiole. Used in Antkey to separate Pheidole fervens, Pheidole obscurithorax and Pheidole teneriffana from Pheidole megacephala.	Lateral view of waist, adult worker. The petiole and postpetiole are covered on all surfaces by a punctate ground sculpture, giving them dull appearances. Used in Antkey to separate the minor worker of Pheidole obsurithorax from that of Pheidole fervens.