Cardiocondyla obscurior is a small (~1.5 mm) nondescript, yellow to yellowish brown species with short antennal scapes and moderately sized propodeal spines, and without erect hairs on its mesosoma. The species is an accomplished tramp ant (Heinze et al., 2006)and has established populations across the world, including northern Europe (Rasplus et al., 2010; Seifert, 2003a), but it is not considered a pest or known to adversely affect native ecosystems. The restriction of the two non-tramp ants in the C. wroughtonii-group to India and Borneo suggest the native range of C. obscurior to be Southeast Asia. Cardiocondyla obscurior is polygynous, and often founds new colonies by nest splitting (Seifert, 2003a). Typical colony sizes are less than 500 workers (Seifert, 2003a). Unlike most of its congeners which nest in the soil, C. obscurior and its close relative C. wroughtonii nest in vegetation above the surface (Deyrup et al., 2000; Lupo & Galil, 1985). The reproductive strategies and caste determination of the species has been extensively studied, especially with respect to ergatoid males (Cremer et al., 2008; Heinze & Delabie, 2005; Heinze & Hölldobler, 1993; Kinomura & Yamauchi, 1987; Schrempf et al., 2007; Stuart et al., 1987).
Cardiocondyla obscurior has commonly been misidentified as C. wroughtonii prior to Seifert’s (2003a)revision, and many of the literature references to the latter in fact refer to the former (e.g. Heinze & Hölldobler, 1993; Kinomura & Yamauchi, 1987; Stuart et al., 1987; Terayama, 1999). However, the species can be difficult to tell apart, and a thorough review of specimens vouchered for these works is needed to determine the correct name of the study species. Seifert offered the following discussion on how to differentiate between the two species.
The best indication for a separate species identity is given by differences in morphometry, gastral pigmentation pattern, and selection of nest habitats. C. obscurior was reported to nest in cavities of bushes and trees 2–5 m above the ground level; it was found in dead twigs of trees such as Erythrina variegata (Okinawa), in dwarf coconuts (Brazil), galls of Acacia trees (Brazil), in a dead twig on a tree (Florida), on a Ficus tree (Israel), in the gall of a Tamarix bush (Israel), and in the cavity of a coconut high in the tree (Zanzibar). C. wroughtonii, in contrast, was reported to nest near to or on the ground; it was found in hollow stems of dead Eulalia grasses (Okinawa), in a dead twig on the ground (New Orleans/USA), between layers of Eugenia jambolana leaves (India), in litter (Sulawesi), and "under leaves in a silk patch" (Tanzania). The workers of C. obscurior differ from C. wroughtonii by darker gaster pigmentation, shorter head, smaller postocular distance, narrower frons, wider and higher waist segments, wider spine base distance, and shorter spine length.
A wide-ranging tramp species, but not considered to be a significant pest.
Diagnosis of worker among Antkey species. Worker caste monomorphic. Head shape subrectangular. Antenna 12-segmented. Antennal club 3-segmented. Antennal scapes easily extended beyond eye level but scapes do not extend beyond posterior margin of head. Antennal scrobe lacking. Antennal insertion not surrounded by a raised sharp-edged ridge. Eyes greater than 6 facets; not unusually large (distinctly less than half head length). Posterolateral corners of head unarmed, without spines. Mandibles triangular. Mesosoma lacking erect hairs. Metanotal groove distinctly impressed. Pronotal spines absent. Propodeal spines relatively long (more developed than small angles). Slope of mesosoma gradual. Waist 2-segmented. Petiole with a distinct and upright node; lacking large subpetiolar process. Petiolar peduncle not appearing long (length not twice height); thickens gradually as it tapers into node. Postpetiole appearing swollen, in dorsal view wider than long and much broader than petiole; attached to lower surface of gaster. Postpetiole as high as petiole and with a distinct ventral bulge, postpetiole in dorsal view with sharp anterolateral corners. Color of gaster often darker than the rest of body. Head, mesosoma, and waist brightly yellowish or yellowish brown, antennal club usually notably infuscated.
Among introduced Cardiocondyla species, C. obscurior (together with C. emeryi and C. wroughtonii) is differentiated by (1) a distinctly impressed metanotal groove, (2) relatively long propodeal spines, and (3) a postpetiole that is as high as the petiole and possessing a distinct ventral bulge. It is distinguished from C. emeryi by the postpetiole, which in dorsal view has sharply angled (versus gently rounded in C. emeryi) anterolateral corners. Seifert (2003a)notes that C. obscurior can often be differentiated from C. wroughtonii by the more bicolored appearance caused by its darker gaster pigmentation, shorter head, smaller postocular distance, narrower frons, wider and higher waist segments, wider spine base distance, and shorter spine length.
Cardiocondyla emeryi, Cardiocondyla wroughtonii.
Native range. Old World tropics, likely SE Asia.
Introduced range. Worldwide.