Myrmecia inquilina
Myrmecia inquilina is a species of ant endemic to Australia in the subfamily Myrmeciinae, first discovered in 1955 and described by Athol Douglas and William Brown Jr. in 1959. These ants are large, measuring . During the time of its discovery, Douglas and Brown announced "M. inquilina" as the first social parasite among the primitive subfamilies, and today it is one of the two known "Myrmecia" species to have no worker caste. Two host species are known, "Myrmecia nigriceps" and "Myrmecia vindex". Aggression between "M. inquilina" and its host species does not occur, and colonies may only produce "M.  inquilina" brood months after the inquiline queens begin to lay their eggs. Queens eat the colony brood or trophic eggs, and other "Myrmecia" species may kill "M. inquilina" queens if they reject them. Due to its restricted distribution and threats to its habitat, the ant is "vulnerable" according to the IUCN Red List. Taxonomy. Before the discovery of "M. inquilina", scientists believed that parasitic ants did not exist in the primitive ant subfamilies and were only known in Dolichoderinae, Formicinae and Myrmicinae; many authors believed that primitive ants lacked a certain trait that would prevent parasitic ants from forming, but  the discovery of "M. inquilina" now hints possible parasitic lifeforms in Ponerinae and some army ants. Brown collected the first specimens in 1955 from large fallen trees in Western Australia, and it was officially announced as the first parasitic ant among the primitive subfamilies in 1956. In 1959, Australian naturalist Athol Douglas and American entomologist William Brown Jr. provided the first description of the ant in an "Insectes Sociaux" journal article. Its specific epithet "inquilina" derives from the word "inquilinus", meaning "tenant". This name references the parasitic nature of the species, living inside a colony as a "guest" of another  species. Brown discovered the holotype female from an "M. vindex" nest on 23 March 1955 northwest from Wagin at Badjanning Rocks, Western Australia. The specimen is currently housed in the Western Australian Museum in Perth. Two dealated paratype females were also collected with the holotype, looking very similar to each other except for the mandibles and colouration. The mandibular dentition varies among the three, and one of the paratypes is darker than the holotype. In 1991, a published journal reviewing the species groups assigned "M. inquilina" to the "M. cephalotes" species group. However, entomologists placed it in the "M. gulosa  species group one month after placing it in the M. cephalotes" species group. Description. "Myrmecia inquilina" is a large species, though it is smaller than its host. The body length of the ant is , the head including the clypeus is , the antennal scape and the diameter of the eyes are . The mandibles are slender with four to five acutely shaped teeth. The antennae are morphologically similar to "M. vindex", but it is smaller in comparison; the petiole node is also longer and wider. The postpetiole is subtriangular and more narrow than those seen on "M. vindex" queens. The clypeus, legs  and antennae are covered in punctulates (spots), and the postpetiole and gaster have less punctulates. "M. inquilina" can be distinguished from other ants due to its lack of pilose (long soft hairs); only small erect setae are mostly found on the mandibles and gastric apex, but short hair can be found on the legs, and on the dorsum, thorax and cervix. The ant has pubescence (soft short hair) finer and more abundant than "M. vindex". The pubescence is greyish in colour, and it is shorter and more noticeable on the clypeus and appendages while it is conspicuous on the postpetiole  and gaster. The colour of the head and gaster are black, shading into reddish brown on the clypeus and around the frontal carinae. The mesosoma (alitrunk), node, and legs are brownish-red and light, with the legs becoming yellowish in certain areas. The antennae and mandibles are brownish yellow, and the teeth have black edges. Overall, "M. inquilina" can be distinguished from others by its black head and its almost hairless body. Its colour is similar to "M. nigriceps", but "M. nigriceps" is larger and covered in hair, along with a head more rounded than other species. "M. inquilina" does  not have a worker caste, making it a workerless parasite. Five males collected from an "M. vindex" nest are presumed to be "M. inquilina", but the similarities between the two species cannot confirm if the males are "M. inquilina". While the males collected are morphologically similar to "M. vindex" males, the head and gaster are darker, and two specimens show a reddish-brown colour at the base of the first gastric segment, a characteristic that does not occur in "M. vindex" males. The genitalia is similar, but a more detailed study can distinguish these features among the two ants . Distribution and habitat. "Myrmecia inquilina" is only found in the south-west of Western Australia, with the holotype collected 225 kilometres (140 miles) from Perth. "M. inquilina" occurs in colonies with "M. vindex" and "M. nigriceps", found in soil, under logs and flat rocks in woodland. They are commonly found in granite outcrops and wooded areas, with trees such as "Corymbia calophylla", "Acacia acuminata" and a large unidentified species of "Allocasuarina" (possibly "Allocasuarina huegeliana") present. The type locality was in an area cleared for agricultural purposes, but some areas were still wooded; many fallen large trees were present. "M. inquilina  is typically found deep inside the nests, around 25 centimetres (10 inches) and can be found next to the queen. Behaviour and ecology. Myrmecia inquilina" is one of the two known "Myrmecia" species to not have a worker caste, and it is an inquiline to "M. nigriceps" and "M. vindex" colonies. "M. inquilina" is a polygynous species; colonies can house between two and several dozen queens, but some of them nesting in the colony are originally from there. Due to this, some "M. inquilina" females are ergatoid ants that lose their wings after eclosing in their cocoons. The parasitic queen(s ) may only coexist indefinitely, but "M. inquilina" queens replace all host brood with their own eggs several months after infiltrating the nest. This only occurs if "M. inquilina" queens eat or destroy the brood laid by their host, and workers will even tend to the brood and protect it from potential invaders. "M. inquilina" queens tend to nest near the host queen and her brood, attended by worker ants without any form of aggression. Observations suggest that parasitic queens feed on trophic eggs laid by workers. Predatory threats only include other "Myrmecia" species; they are rejected by a potential host  colony. For example, "M. regularis" workers immediately seize "M. inquilina" queens and kill it as soon as the two species come into contact. Aerial dispersion is important in this species, despite its restricted distribution. Queens never forage outside or leave the nest, unless under severe deprivation. Before nuptial flight, fully developed females start to occur during summer. Between 9 and 10 pm in January, queens and males start to emerge from their host nest and begin to mate. Observations show that the alates will climb up onto objects such as lighted fluorescent lamps and begin to fly after half an  hour of endless running. When queens are looking for a host nest or wandering openly, "M. vindex" foragers may identify a queen and seize her; such behaviour suggests that workers actively recruit fertilised queens for their nest. Host colonies tend to be smaller and depauperated when compared to other colonies without any inquiline queens, but host colonies can still produce alate offspring. Status. "Myrmecia inquilina" is the only species in its genus to be listed as "vulnerable" by the IUCN Red List. This, however, needs updating. Habitat loss may be responsible for the ant to be potentially endangered; Douglas and  Brown note that a contamination of dieldrin spray to control the argentine ant destroyed many nests housing "M. inquilina", and burn-offs are also a threat to colonies housing "M. inquilina".