Camponotus (Tanaemyrmex) irritans ( Smith, 1857 )

Hamer, Matthew T., Lee, Jonathan Hon Chung, Tse, Cheung Yau Leo, Silva, Thiago S. R. & Guénard, Benoit, 2022, Remarkable diversity in a little red dot: a comprehensive checklist of known ant species in Singapore (Hymenoptera: Formicidae) with notes on ecology and taxonomy, Asian Myrmecology (e 015006) 15, pp. 1-152 : 42-43

Camponotus (Tanaemyrmex) irritans ( Smith, 1857)

Material examined. Lee Kong Chian Natural History Museum bus stop, 13 Jan 2017, S.H. Tan leg., nest in junction box, WW-SG17-007, ZRC _ HYM_0000575; Kranji Road , Sep-Nov 2016, G.W. Yong et al. leg., ZRC _ ENT00057823-57827 ; Upper Thomson Nature Park , 11-13 Sep 2016, G.W. Yong et al. leg., ZRC _ ENT00057828 ; Seletar Link , 23-25 Oct 2016, same collectors as previous, ZRC _ ENT00057829 ; Mandai Road , 29 Nov – 1 Dec 2016, G.W. Yong et al. leg., ZRC _ ENT00057830 ; Sunset Way , 31 Aug 2016, G.W. Yong et al. leg., ZRC _ ENT00057831 .

Material not physically examined. Unknown.

Literature. Wang et al. (2018a) - but see Remarks for Camponotus carinifer .

Localities. Kranji Road; Lee Kong Chian Natural History Museum ( NUS); Mandai Road; Seletar Link; Sunset Way.

Habitat/Ecology. These ants appear to be quite tolerant of degraded or disturbed environments, able to thrive in areas near man-made infrastructure as well as young or mature secondary forest fragments. A colony was even found nesting inside an outdoor electrical junction box next to a building in urban settings. The ants are commonly observed (unverified sightings), sometimes photographed, but not collected. The species is probably more widespread locally than is represented in formal museum holdings, not limited to the two localities listed in this section. In recent times, these ants have apparently also become increasingly popular in the local pet trade.

Remarks. As mentioned before (see Remarks for C. carinifer ), C. irritans was first described based on two minor workers – a large one (> 12 mm) and another roughly half its size (which Smith defined as truly ‘minor’). The

major worker was never formally described. This is problematic with regards to species delimitation, especially for species of the subgenus Tanaemyrmex , as the worker caste can be extremely polymorphic.

Within each colony sample we examined, we observed a broad spectrum of intermediate worker forms, varying mainly in head shape, size, and body colours. Nevertheless, the elongate and slender habitus, characteristic of C. irritans as it was first described, persists across all variants, including teneral individuals. It is difficult to clearly define the boundaries separating ‘majors’ from ‘minors’ because of the apparent continuum of forms. As expected, Smith’s (1857) original description and the online type image of C. irritans matched only with a few individuals per sample. Major workers, also variable in head shape, resemble those of Camponotus carin Emery, 1889 and other close relatives. Minor workers of different species of Camponotus can be almost identical to each other. Some minor workers of the C. irritans colonies we examined, for example, closely matched the original description and type image for Camponotus mitis ( Smith, 1858) , except for petiole shape. Consequently, we cannot overlook the possibility that specimens we currently recognize as “ C. irritans ” may in fact belong to another similar species of the subgenus Tanaemyrmex .