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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, 2003), 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, 2003). Typical colony sizes are less than 500 workers (Seifert, 2003). 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).
Native range. Old World tropics, likely SE Asia.
Introduced range. Worldwide.
Fiji: Beqa: Malovo 182. Kadavu: Moanakaka 60. Macuata: Vunitogoloa 10. Moala: Naroi 75. Vanua Levu: Vusasivo Village 400 b, Rokosalase 97, Lagi 300. Viti Levu: Mt. Evans 800, Mt. Evans 800, Navai 700, McDonalds Resort 10 b, Mt. Batilamu 840 c, Ellington Wharf 1, Volivoli 55.
Cardiocondyla obscurior has commonly been misidentified as C. wroughtonii prior to Seifert’s (2003)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.).
In Costa Rica (Jack Longino). I collected this species from a treetrunk in front of the Juan Santa Maria International Airport, in a landscaped area. Joel Dunn collected a nest from the domatium of a Cordia alliodora tree at La Selva Biological Station. John Noyes collected workers in sweep samples from La Selva.
In Fiji (Eli Sarnat): Cardiocondyla obscurior is one of the more commonly collected species of the genus in Fiji, and occurs around disturbed habitats on six of the islands. Its presence in malaise traps suggests an arboreal habit.
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 (2003)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.
Diagnosis among workers of introduced and commonly intercepted ants in the United States. 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 5 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.
Cremer, S., D'Ettorre, P., Drijfhout, F.P., Sledge, M.F., Turillazzi, S. & Heinze, J. (2008) Imperfect chemical female mimicry in males of the ant Cardiocondyla obscurior. Naturwissenschaften, 95, 1101-1105.
Heinze, J., Cremer, S., Eckl, N. & Schrempf, A. (2006) Stealthy invaders: the biology of Cardiocondyla tramp ants. Insect. Soc., 53, 1-7.
Heinze, J. & Delabie, J.H.C. (2005) Population structure of the male-polymorphic ant Cardiocondyla obscurior. Stud. Neotrop. Fauna Environ., 40, 187-190.
Heinze, J. & Hölldobler, B. (1993) Fighting for a harem of queens: physiology of reproduction in Cardiocondyla male ants. Proc. Natl. Acad. Sci. U.S.A., 90, 8412-8414.
Kinomura, K. & Yamauchi, K. (1987) Fighting and mating behaviors of dimorphic males in the ant Cardiocondyla wroughtoni. J. Ethol., 5, 75-81.
Lupo, A. & Galil, J. (1985) Nesting habits of Cardiocondyla wroughtoni Forel (1890) (Hymenoptera: Formicidae). Isr. J. Entomol., 19, 119-125.
Rasplus, J.Y., Villemant, C., Paiva, M.R., Delvare, G. & Roques, A. (2010) Hymenoptera. BioRisk, 4(2), 669-776.
Schrempf, A., Darrouzet, E. & Heinze, J. (2007) Mating success and potential male-worker conflict in a male-dimorphic ant. BMC Evol. Biol., 7:114, 8 p.
Sarnat, E.M. & Economo, E.P. (In Press) Ants of Fiji. University of California Publications in Entomology.
Seifert, B. 2003. The ant genus Cardiocondyla (Insecta: Hymenoptera: Formicidae): A taxonomic revision of the C. elegans, C. bulgarica, C. batesii, C. nuda, C. shuckardi, C. stambuloffii, C. wroughtonii, C. emeryi, and C. minutior species groups. Annalen des Naturhistorischen Museums in Wien Serie B Botanik und Zoologie 104B:203-338.
Stuart, R.J., Francoeur, A. & Loiselle, R. (1987) Lethal fighting among dimorphic males of the ant, Cardiocondyla wroughtonii. Naturwissenschaften, 74, 548-549.
Terayama, M. (1999) Taxonomic studies of the Japanese Formicidae, Part 6. Genus Cardiocondyla Emery. Mem. Myrmecol. Soc. Jpn., 1, 99-107.
Ward, D.F. (2007) The distribution and ecology of invasive ant species in the Pacific Region. PhD thesis, in Biological Sciences, The University of Auckland, xiii + 173 p.
Found most commonly in these habitats: 7 times found in mixed forest, 3 times found in primary rainforest, 1 times found in second growth veg., 2 times found in non native forest, 3 times found in disturbed forest, 3 times found in littoral forest, 2 times found in lowland wet forest, 2 times found in beach hut, 1 times found in campus of Stetson University, 2 times found in secondary forest, ...
Collected most commonly using these methods or in the following microhabitats: 4 times search, 3 times hand, 3 times Winkler, 1 times Beating, 2 times malaise, 1 times tuna bait, 1 times bait, 1 times foraging, 1 times hand collection, 1 times M, 1 times sweep net, ...
Elevations: collected from 1 - 1930 meters, 357 meters average
Type specimens: Holotype of Cardiocondyla bicolor: casent0901754