Cardiocondyla obscurior
Cardiocondyla minutior is a small (~ 1.5 mm), nondescript, yellowish brown to blackish brown species with short antennal scapes and moderately sized propodeal spines, and without erect hairs on its mesosoma. The C. minutior species group reaches its greatest diversity in the Indomalayan region, and may be the ancestral area of C. minutior prior to its dispersal across much of the globes tropical and subtropical regions (Seifert, 2003a). Despite its success at invading new habitats (Heinze et al., 2006), C. minutior remains an inconspicuous member of the ant fauna across its range, and is not reported to cause harm to either humans or native species.
Cardiocondyla minutior is known to be polydomous and polygynous and founds new colonies preferentially by nest splitting (Seifert, 2003a), and is presumed to form small colonies and subsist on an omnivorous diet similar to its trampy congeners. Data from specimens on Antweb show C. minutior is most frequently collected in synanthropic habitats across its range, and in Okinawa the species was reported by K. Yamauchi to nest in shallow soil in open, disturbed areas with bare or weakly herbaceous ground (in Seifert, 2003a). Video footage of C. minutior foragers tandem running was taken in Fiji (Sarnat, 2008a).
The male caste of C. minutior is dimorphic. Wingless, ergatoid males of the tramp ant Cardiocondyla minutior attack & kill their young ergatoid rivals in an attempt to monopolize mating with female gynes reared within the colony (Heinze et al., 2004; Terayama, 1999). It has been suggested that wingless ergatoid males mate within natal nests, whereas winged males bearing typical ant male morphology disperse from their nests to mate, but the actual reproductive strategies employed by the different morphs is actually more nuanced (Yoshizawa et al., 2011).
Not considered a significant pest species.
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 absent to shallow; not distinctly impressed. Pronotal spines absent. Propodeal spines of moderate length. 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 postpetiole wider than long and much broader than petiole; with gently rounded anterolateral corners. Postpetiole lower than petiole and lacking a distinct ventral bulge. Upper surface of gaster attached to postpetiole. Color of head, mesosoma, and waist varying considerably from dirty yellowish to dark dirty brown, gaster dark to blackish brown.
Among introduced Cardiocondyla species, C. minutior (together with C. kagutsuchi, C. mauritanica and C. venustula) is differentiated from C. emeryi, C. obscurior and C. wroughtonii by (1) its weakly impressed to absent metanotal groove; and (2) a postpetiole that is lower than the petiole and lacking a distinct ventral bulge. Its propodeal spines are longer than the short angles of C. kagutsuchi, C. mauritanica and C. venustula, but shorter than the spines of C. emeryi, C. obscurior and C. wroughtonii. Additionally, C. minutior is separated from C. kagutsuchi and C. mauritanica by its shorter petiolar peduncle which gradually tapers into the node, and from C. obscurior and C. wroughtonii by the more gently rounded anterolateral corners of the postpetiole when observed in dorsal view.
Cardiocondyla kagutsuchi, Cardiocondyla mauritanica, Cardiocondyla venustula.
Native range. Indomalayan region.
Current distribution includes. Islands of the Indian Ocean, India, Sri Lanka, Nepal, Japan, Polynesia, Indonesia, New Guinea, Fiji, New Zealand, Florida, entire Caribbean.