Chelaner antarcticus

Chelaner antarcticus is an ant of the family Formicidae, endemic to New Zealand. Also known as the southern ant, this is likely New Zealand's most common native ant species. Because it is highly variable in size (3–5mm), colour, and colony structure, it is possible that it consists of a complex of closely related species. It has a generalist diet that includes small arthropods, nectar, and seeds, and it also tends to aphids, scale insects, and mealybugs to obtain honeydew.^[1]

This species was described by Frederick Smith in 1858 as Atta antarctica,^[2] and was placed in the large and extremely diverse genus Monomorium in 1886.^[3]

By the early 20th century Monomorium contained 10 subgenera, one of which was Monomorium (Chelaner) Emery, 1914. Chelaner was raised to generic level in 1966 to contain 37 Australian species along with 10 from New Caledonia, New Guinea, and New Zealand.^[4]

Bolton in 1987 examined the mophological features of Chelaner, and found them to be too variable to distinguish the genus, which was synonymised with Monomorium again.^[5] In 2019 after a comprehensive study of multiple genes the genus Chelaner was resurrected, to house a total of 53 Australasian and Pacific species, including this one, which would then be known as Chelaner antarcticus.^[6]

It is commonly referred to as the "southern ant".^[7]

Worker specimens are variable in size, usually 3–5 millimetres (0.12–0.20 in) in length, with head width varying from 0.60–0.88 millimetres (0.024–0.035 in).^[8] The antennae have 12 segments, with a three segmented club.^[8] A metanotal groove present, either distinctly or weakly impressed.^[8] Spines on the propodeum are either blunt or absent.^[8] The colour highly variable across colonies (but usually consistent within colonies), ranging from orange, light to dark brown, and black.^[8]

Chelaner antarcticus is endemic to New Zealand where it is widespread in the North and South Island as well as Stewart Island.^[8] It is also present on smaller offshore islands such as the Three Kings Islands, the Chatham Islands, the Kermadec Islands and even the far away Austral Islands in Polynesia.^{[9][10][11][12]} It is found throughout many habitats including native forest, grasslands, wetlands, pastureland, household gardens as well as horticultural and industrial habitats.^{[13]: 33 [14]: 11} There is evidence that its range in urban habitats may be restricted due to competition with invasive ant species (such as Linepithema humile), at least in northern parts of New Zealand.^[14]: 11

The winged male and female can sometimes be found in flying swarms, being so numerous that they make an audible humming sound.^[15]

The nest is constructed in rotting logs or in the ground. If its built in the ground, it is often under a stone or log.^[13]: 33

The larvae of the fly Helosciomyza subalpina have been recorded feeding on the larvae of C. antarcticus in laboratory conditions, apparently showing a preference for it over other food sources. The fly larvae use their mouth-hooks to erode a hole into the ant larvae and then feed on liquid from the holes. In nature, the fly larvae have been found living in the nests of C. antarcticus in large numbers.^[16] Diplotoxa moorei, another species of fly, is also associated with the nest of C. antarcticus.^[17]

In one study, C. antarcticus was more common in the southern parts of the country. It was proposed that this is due to the presence of invasive ants in the north restricting their abundance, although more research is needed to confirm this.^[18]: 513 There are several species that C. antarcticus rarely co-occurs with. It was found that when the invasive Doleromyrma darwiniana was present in surveys, C. antarcticus would never be caught.^[19] In another study, it was found that C. antarcticus fed at a similar trophic level and had high niche overlap with the invasive Ochetellus glaber, which it also doesn't co-occur with. This suggests that they are undergoing competitive exclusion.^{[20]: 92–93} The ants distribution also overlaps very little with Prolasius advenus, another common endemic ant species. A couple of studies suggest that environmental factors such as diet, arrival sequence when colonising new areas, colony size and temperature collectively act as a filter which causes the two species to rarely co-occur.^{[21]: 90 [22]: 463}

Media related to Chelaner antarcticus at Wikimedia Commons

• Southern Ant discussed on RNZ Critter of the Week, 31 March 2023