Myrmecia is a genus of ants first established by Danish zoologist Johan Christian Fabricius in 1804. The genus is a member of the subfamily Myrmeciinae of the family Formicidae. Myrmecia is a large genus of ants, comprising at least 93 species that are found throughout Australia and its coastal islands, while a single species is only known from New Caledonia. One species has been introduced out of its natural distribution and was found in New Zealand in 1940, but the ant was last seen in 1981. These ants are commonly known as bull ants, bulldog ants or jack jumper ants, and are also associated with many other common names. They are characterized by their extreme aggressiveness, ferocity, and painful stings. Some species are known for the jumping behavior they exhibit when agitated.
Species of this genus are also characterized by their elongated mandibles and large compound eyes that provide excellent vision. They vary in colour and size, ranging from . While workers and queens are hard to distinguish from each other due to their similar appearance, males are identifiable by their perceptibly smaller mandibles. Almost all Myrmecia species are monomorphic, with little variation among workers of a given species. Some queens are ergatoid and have no wings, while others have either stubby or completely developed wings. Nests are mostly found in soil, but they can be found in rotten wood and under rocks. One species does not nest in the ground at all; its colonies can only be found in trees.
A queen will mate with one or more males, and during colony foundation she will hunt for food until the brood have fully developed. The life cycle of the ant from egg to adult takes several months. Myrmecia workers exhibit greater longevity in comparison to other ants, and workers are also able to reproduce with male ants. Myrmecia is one of the most primitive group of ants on earth, exhibiting differentiated behaviors from other ants. Workers are solitary hunters and do not lead other workers to food. Adults are omnivores that feed on sweet substances, but the larvae are carnivores that feed on captured prey. Very few predators eat these ants due to their sting, but their larvae are often consumed by blindsnakes and echidnas, and a number of parasites infect both adults and brood. Some species are also effective pollinators.
Myrmecia stings are very potent, and the venom from these ants is among the most toxic in the insect world. In Tasmania, 3% of the human population are allergic to the venom of M. pilosula and can suffer life-threatening anaphylactic reactions if stung. People prone to severe allergic reactions can be treated with allergen immunotherapy (desensitisation).
Etymology and common names The generic name Myrmecia derives from Greek word Myrmec- (+ -ia), meaning "ant". In Western Australia, the Indigenous Australians called these ants kallili or killal.
Ants of this genus are popularly known as bulldog ants, bull ants, or jack jumper ants due to their ferocity and the way they hang off their victims using their mandibles, and also due to the jumping behaviour displayed by some species. Other common names include "inch ants", "sergeant ants", and "soldier ants". The jack jumper ant and other members of the Myrmecia pilosula species group are commonly known as "black jumpers", "hopper ants", "jumper ants", "jumping ants", "jumping jacks", and "skipper ants".
Taxonomy and evolution
Genetic evidence suggests that Myrmecia diverged from related groups about 100 million years ago (Mya). The subfamily Myrmeciinae, to which Myrmecia belongs, is believed to have been found in the fossil record of 110 Mya ago. However, one study suggests that the age of the most recent common ancestor for Myrmecia and Nothomyrmecia is 74 Mya, and the subfamily is possibly younger than previously thought. Ants of the extinct genus Archimyrmex may possibly be the ancestor of Myrmecia. In the Evans' vespoid scala, Myrmecia and other primitive ant genera such as Amblyopone and Nothomyrmecia exhibit behavior which is similar to a clade of soil-dwelling families of vespoid wasps. Four species groups form a paraphyletic assemblage while five species groups form a monophyletic assemblage. The following cladogram shows the phylogenetic relationships within Myrmecia:
Classification
Myrmecia was first established by Danish zoologist Johan Christian Fabricius in his 1804 publication Systema Piezatorum, in which seven species from the genus Formica were placed into the genus along with the description of four new species. Myrmecia has been classified into numerous families and subfamilies; in 1858, British entomologist Frederick Smith placed it in the family Poneridae, subfamily Myrmicidae. It was placed in the subfamily Ponerinae by Austrian entomologist Gustav Mayr in 1862. This classification was short-lived as Mayr reclassified the genus into the subfamily Myrmicinae three years later. In 1877, Italian entomologist Carlo Emery classified the genus into the newly established subfamily Myrmeciidae, family Myrmicidae. Smith, who had originally established the Myrmicidae as a family in 1851, reclassified them as a subfamily in 1858. He again treated them as a family in 1871. Swiss myrmecologist Auguste Forel initially treated the Poneridae as a subfamily and classified Myrmecia as one of its constituent genera but later placed it in the Ponerinae. William H. Ashemad placed the genus in the subfamily Myrmeciinae in 1905, but it was later placed back in the Ponerinae in 1910 by American entomologist William Morton Wheeler. In 1954, Myrmecia was placed into the Myrmeciinae; this was the last time the genus was placed into a different ant subfamily.
In 1911, Emery classified the subgenera Myrmecia, Pristomyrmecia, and Promyrmecia, based on the shape of their mandibles. Wheeler established the subgenus Halmamyrmecia, and the ants placed in it were characterized by their jumping behavior. The taxon Wheeler described was not referred to in his later publications, and the genera Halmamyrmecia and Pristomyrmecia were synonymised by John Clark. At the same time, Clark reclassified the subgenus Promyrmecia as a full genus. He revised the whole subfamily Myrmeciinae in 1951, recognizing 118 species and subspecies in Myrmecia and Promyrmecia; five species groups were assigned to Myrmecia and eight species groups to Promyrmecia. This revision was rejected by entomologist William Brown due to the lack of morphological evidence that would make the two genera distinct from each other. Due to this, Brown classified Promyrmecia as a synonym of Myrmecia in 1953. Clark's revision was the last major taxonomic study on the genus before 1991, and only a single species was described in the intervening years. In 2015, four new Myrmecia ants were described by Robert Taylor, all exclusive to Australia. Currently, 94 species are described in the genus, but as many as 130 species may exist.
Under the present classification, Myrmecia is the only extant genus in the tribe Myrmeciini, subfamily Myrmeciinae. It is a member of the family Formicidae in the order Hymenoptera. The type species for the genus is M. gulosa, discovered by Joseph Banks in 1770 during his expedition with James Cook on HMS Endeavour. M. gulosa is among the earliest Australian insects to be described, and the specimen Banks collected is housed in the Joseph Banks Collection in the Natural History Museum, London. M. gulosa was described by Fabricius in 1775 under the name Formica gulosa and later designated as the type species of Myrmecia in 1840.
Genetics The number of chromosomes per individual varies from one to over 70 among the species in the genus. The genome of M. pilosula is contained on a single pair of chromosomes (males have just one chromosome, as they are haploid). This is the lowest number possible for any animal, and workers of this species are homologous. Like M. pilosula, M. croslandi also contains a single chromosome. While these ants only have a single chromosome, M. pyriformis contains 41 chromosomes, while M. brevinoda contains 42. The chromosome count for M. piliventris and M. fulvipes is two and 12, respectively. The genus Myrmecia retains many traits that are considered basal for all ants (i.e. workers foraging alone and relying on visual cues).
Species groups Myrmecia contains a total of nine species groups. Originally, seven species groups were established in 1911, but this was raised to 13 in 1951; Promyrmecia had a total of eight, while Myrmecia only had five. M. maxima does not appear to be in a species group, as no type specimen is available.