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Aneuretus simoni, commonly known as the Sri Lankan Relict Ant, is the only known extant member of the subfamily Aneuretinae. Several other genera are described from Tertiary fossils found in Baltic amber, Russia and the USA, indicating a previous much wider distribution and diversity .
In major and minor workers, body color varies from light yellow to medium yellowish orange. Antennae 12-segmented. Clypeus broad and flat. Three segmented maxillary palp and four segmented labial palp present. Mandibles triangular, with three prominent teeth and several denticles; their size gradually decreases from apex to the base. A pair of spike-like, posterior, propodeal spines taper abruptly towards the tips. Anterior peduncle of the petiole is long and slender, somewhat narrowed towards its anterior attachment. The petiolar node is well differentiated from the anterior peduncle by dorsal and lateral swellings. Sting at the tip of the gaster is well developed and sclerotized. The major worker differs from the minor worker primarily in its proportionately larger and broader head and relatively shorter and stouter propodeal spines. Total length and head length of a major worker range from 2.2 to 2.3 mm and 0.54 to 0.58 mm, respectively, while those of a minor worker range from 1.7 to 1.9 mm and 0.44 to 0.55 mm, respectively .
The several studied colonies were found to have 18–106 minor workers and just 1–3 major workers. Major workers undertake a more limited set of colony-maintaining tasks, which appear not to include brood care or any defense against intruders. Minor workers care for the brood (including assisting in their pupation and eclosion) and the queen, maintain and defend the nest, and forage outside the nest. Where a colony has two queens, they are both observed to lay eggs without any evident aggression [6, 11].
As eggs are laid, they are placed in a pile by workers . In laboratory colonies, workers were also observed to lay infertile trophic eggs . Upon hatching, larvae are cleaned up by the workers and then placed directly on food consisting of fresh insect fragments. Prior to pupation, larvae are licked clean by workers and then covered with soil particles. Cocooning and pupation take about 4 h, after which the workers remove the debris and carry the pupa to a different area of the nest where it will remain until adult emergence. Shortly before emergence, workers gather around a pupa, make small incisions in the cocoon, and extract the callow adult, which remains inactive for a day or more . In the laboratory, workers complete development from egg to adult in 4 weeks .
Distribution and Habitats
Favorable environmental conditions include high rainfall (2000 mm or more per years), mean daily air temperature of 26–29 °C, mean soil temperature of 24–29 °C and 13–40% soil moisture, and around 8% soil organic matter [2, 4, 5, 7, 10].
Few studies have quantified the nest densities of A. simoni. Three study plots in Gilimale Forest Reserve showed 0.017, 0.023, and 0.033 colonies per m2 , while some other study areas had higher nest density of the species [4, 10].
Foragers have generalized habits, best characterized as omnivorous scavengers with occasionally feeding on rotten fruit and nectar, as very small insects encountered in the leaf litter. Prey are paralyzed by stinging .
Exocrine System, Chemical Communication, and Social Behavior
Recruitment communication among workers is mediated by the secretions of the sternal gland, while alarm substances are produced in the pygidial gland . The sternal gland, which produces a long-lasting mass recruitment pheromone, comprises a glandular epithelium and an associated reservoir located in the seventh sternum. The pygidial gland opens between the sixth and seventh terga. Although A. simoni has many primitive features, in its extensive use of chemical signals, it shows a level of sophistication comparable to that of “advanced” ant groups [1, 8].
The morphology of the 11 exocrine glands of the workers was described recently . A profile drawing of a minor worker shows a well-developed intramandibular gland, epithelial gland, mandibular gland, propharyngeal gland, postpharyngeal gland, labial gland (salivary gland), a paired metapleural gland with the lowest number of secretory cells known in ants , a well-developed venom gland with long and slender secretory filaments, a bilobed Pavan’s (sternal) gland , Dufour’s gland, and the pygidial gland. It is suggested that yet other glands may be discovered in the legs, which have not yet been studied .
The size of the minor workers’ behavioral repertory resembles that of some dolichoderine ants. There is also much overlap with behavior patterns recorded from various formicine and myrmicine genera. Trophallaxis, trail communication, movement of workers between nests, chemically organized nest emigration, and group retrieval of prey are prominent features of A. simoni’s foraging . Transportation of adults begins with a brief interchange of invitation signals that induce tonic immobility in the individual to be carried, which is not recorded from dolichoderines, but is present in many other ants.
Most known A. simoni localities are in forest reserves, so that the species is protected by law. Surveys from 2001 to 2018 showed that it has a wide distribution in disturbed forests (e.g. Pompekelle and Kirikanda forests), and at least one forest reserve in each district of Sri Lanka’s wet zone. It is also recorded in two intermediate zone forests, although nowhere in the dry zone. Contrary to earlier assessments, thus, it does not appear to merit Critically Endangered status.
DNA Barcode of the Species
Global Barcode of Life Data Mirror () provides the amino acid sequence of A. simoni.
- 1.Billen, J. (2017). The exocrine system of Aneuretus simoni (Formicidae, Aneuretinae). Asian Myrmecology, 9, 1–16.
- 2.Dias, R. K. S. (2014a). Aneuretus simoni Emery occurrence and the ant community observed by multiple methods and repeated sampling in “Pompekelle”, Sri Lanka. International Journal of Entomological Research, 2, 181–186.
- 3.Dias, R. K. S. (2014b). Ants of Sri Lanka. Colombo: Biodiversity Secretariat of Ministry of Environment and Renewable Resources. 273.
- 4.Dias, R. K. S., & Udayakantha, W. S. (2016a). Discovery of the Sri Lankan Relict Ant, Aneuretus simoni Emery (Formicidae, Aneuretinae) and the nest density of the species in a selected region of Meethirigala Forest Reserve, Sri Lanka. Asian Myrmecology, 8, 1–8.
- 5.Dias, R. K. S., & Udayakantha, W. S. (2016b). Nest density and other observations on a population of Aneuretus simoni Emery, 1893 (Formicidae, Aneuretinae) and other ants in Indikada Mukalana Forest Reserve in Sri Lanka. Journal of Insect Biodiversity, 4(12), 1–9.
- 6.Jayasuriya, A. K., & Traniello, J. F. A. (1985). The biology of primitive ant Aneuretus simoni Emery (Formicidae: Aneuretinae) I, distribution, abundance, colony structure and foraging ecology. Insectes Sociaux, Paris, 32, 363–374.
- 7.Perera, K. A. M., Dias, R. K. S., & Yamane, S. (2006). The first record of Aneuretus simoni Emery (Sri Lankan Relict ant) from Sinharaja Forest and its relative abundance estimated by several sampling methods. Proceedings of the Annual Sessions of Sri Lanka Association for the Advancement of Science, 62, 74.
- 8.Traniello, J. F. A., & Jayasuriya, A. K. (1981). Chemical communication in the primitive ant Aneuretus simoni: The role of the sternal and pygidial glands. Journal of Chemical Ecology, 7, 1023.
- 9.Udayakantha, W. S., & Dias, R. K. S. (2017). Life history of Sri Lankan relict ant, Aneuretus simoni Emery, 1893 (Formicidae, Aneuretinae) under laboratory conditions. In Proceedings of the international conference in zoological sciences. Patiala: University of Punjabi, 53.
- 10.Udayakantha, W. S., & Dias, R. K. S. (2019). Nest density dynamics and worker occurrence of Aneuretus simoni Emery, 1893 (Formicidae: Aneuretinae) and associated ant taxa in a Forest Reserve in Kegalle District, Sri Lanka. Caucasian Entomological Bulletin, 15 (1), 177–185.
- 11.Wilson, E. O., Eisner, T., Wheeler, G. C., & Wheeler, J. (1956). Aneuretus simoni Emery, a major link in ant evolution. Bulletin of the Museum of Comparative Zoology, 115, 81–105.