Cardiocondyla obscurior Wheeler, W.M., 1929

Ivanov, Kaloyan, 2016, Exotic ants (Hymenoptera, Formicidae) of Ohio, Journal of Hymenoptera Research 51, pp. 203-226 : 211-212

Cardiocondyla obscurior Wheeler, W.M., 1929

Distribution in Ohio.

Single record from southern Ohio. Counties: Hamilton (material examined: Cincinnati, 27-28.vii.2008, leg. R. Gibson and M. Gates, in a conservatory), (Fig. 3 ).

Where found/Habitat.

Indoors, in a conservatory.

Origin.

Australasia.

Natural history.

This is an Old World genus of small, omnivorous ants that contains several cosmopolitan tramp species ( Seifert 2003). Whereas most invasive and pest ants readily make themselves apparent, the presence of these minute ants in a given area often can remain undetected. Cardiocondyla obscurior is a species with well-known dispersal ability that has established populations in many parts of the world ( Heinze et al. 2006). Individuals are readily distinguished by their swollen, heart-shaped postpetiole and the lack of erect hairs on the body (Fig. 4 ).

This is a species with arboreal nesting habits and its small colonies (usually <500 individuals) are typically located in nest cavities on low (2-5m) vegetation, or in folded leaves above ground. Similar to many other ants with small colonies, workers of this species do not defend foraging areas or food resources thus colonies can reach very high densities ( Heinze et al. 2006). The members of this genus are ecologically subordinate and avoid competition with larger and more aggressive ants. As such they are among the few ants that can coexist with known invasives such as the Argentine ant ( Carpintero et al. 2004).

It appears that colonies of all tramp Cardiocondyla species are polygynous and new colonies are formed via budding ( Seifert 2003). In at least Cardiocondyla obscurior , enhanced propagation rates have been attributed to this species’ ability to develop complete and fully functional colonies from very small colony fragments ( Heinze et al. 2006). Given the small size of both workers and colonies of this species, such fragments can be easily transported to new localities in small samples of soil or plant material. Unusual among ants, species of this genus have long-lived ergatoid males (in addition to winged males) which usually stay and mate in their natal nests (intranidal mating) resulting in rigorous competition for virgin queens even among closely related males ( Seifert 2003).

Due to their small colony size, and the fact that workers forage mostly solitary, members of Cardiocondyla are generally not considered pest species ( Heinze et al. 2006). This tropical tramp species can survive in Ohio only in heated buildings.

Figures

Figure 3. Distribution of Cardiocondyla obscurior (5), Monomorium pharaonis (6), Pheidole bilimeki (7), Tetramorium atratulum (8), and Hypoponera ragusai (9) in Ohio.

Figure 4. Lateral view of Cardiocondyla obscurior worker (www. antweb. org, specimen CASENT 0103429, photo: A. Nobile).