Calomyrmex

Calomyrmex are spectacularly coloured, iridescent ants (often blue, purple or green) that are found throughout Australia as well as in Papua New Guinea and Indonesia. They resemble Camponotus but possess a metapleural gland and the workers are monomorphic.

Workers are alert and surface foraging and have the amusing habit of running around frantically with their golden gasters raised when disturbed. They also secrete a coloured fluid from their mandibles which serves as an additional alarm pheromone as well as a defense mechanism as it is highly repulsive. The colour of the fluid changes with the age of the worker, being white or yellowish in young workers and orange in older workers.

Identification
Diagnosis (worker): Formicine ants of the Camponotini tribe, most easily separated from almost all Camponotus and Polyrhachis by the presence of metapleural gland and lack of spines or tubercles on any body parts. Additionally, workers of Calomyrmex are monomorphic, with first gastral segment usually covering less than half of total gaster length. Cuticle with strong iridescence. Ants secrete fluid from mandibular glands when disturbed.

Biology
Natural history: The ants were reported to nest low on trees in lowland rainforest of New Guinea (C. laevissimus; Wilson 1959) or in the ground in arid and semi-arid Australia (Brough 1976). Elaine Brough was the only serious student of Calomyrmex bionomics, and in a series of papers, working on an Australian species related to C. splendidus, she described nests and some elements of behavior (1976) and detailed treatment of mandibular gland structure and function (1977, 1978, 1983). In the 1976 paper she studied nests built by the ants in sandy soils of mallee scrub of New South Wales. After excavation of lead casts, the nests were figured and can be described as mainly composed of a series of chambers and galleries immediately below ground and a long main shaft reaching at least 75 cm deep (apparently continuing deeper, but no complete nest was ever excavated due to hard substrate below). The nest entrances at the study site were clumped in several groups and workers from the neighboring entrances showed no aggressive behavior towards each other but would fight with ants from other groups, suggesting polydomy. Workers were also observed carrying brood between nest entrances.

The ants were active foraging in the morning and late afternoon, but not at night. Workers were seen foraging individually, mostly collecting honeydew, extrafloral nectaries and, occasionally, insect carcasses. Brough also noted that the mandibular gland secretion is white or yellowish in workers nursing brood inside nests, but always orange in foragers found outside the nest.

In a detailed paper on the structure of the glands, she found the reservoirs in workers to be enormous in comparison with other ants, but of similar general structure and found changes in color of the secretion to be correlated with workers age (young- white, becoming orange as the ant ages), and correlated them with changes in the structure of secretory cells (1977). In a later paper (Brough 1978) she investigated potential functions of the gland and found that the secretion induced alarm response among Calomyrmex ants and acts as a repellent of other ant species (Iridomyrmex) and various vertebrates, particularly marsupials, but at the same time it is apparently not toxic. She also speculated about possible aposematic role of scarlet droplets of secretion, which are very conspicuous against dark background of the ant’s head. Brown and Moore (1979) described chemical components of the gland secretion and established that the pyrazine derivatives play role in alarm response but found no behavioral role for other volatiles.

Castes
Workers are monomorphic.

Nomenclature
Name is derived from Greek kalos - beautiful and myrmex - ant -


 *  CALOMYRMEX [Formicinae: Camponotini]
 * Calomyrmex Emery, 1895j: 772. Type-species: Formica laevissima, by monotypy.

Taxonomic history
In 1859 a British hymenopterist, Frederick Smith, described Formica laevissima from the collection of ants, bees, and wasps collected by the famous Alfred Russell Wallace during his voyages in South-East Asia. This species was later moved to Camponotus by Mayr. Eventually, Calomyrmex was described by Emery, who moved C. laevissimus to the newly established genus. A year later Emery moved several further species (mostly described earlier by Mayr and Forel) from Camponotus to Calomyrmex, in his rearrangement of the genera Camponotus, Polyrhachis, and relatives (1896). Nevertheless, as late as 1910 Forel described two further Camponotus subspecies that were eventually transferred to Calomyrmex by Emery in his volume for the Genera Insectorum (Emery 1925). In 1930 John Clark described Calomyrmex glauerti from Australia and... Well, basically that’s it. There is no recent taxonomic treatment or even description of a single species after WWII ! (Marek Borowiec web)