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Iridomyrmex anceps is a dull, light to dark brown polymorphic species with large inset eyes high on the head, dense pubescence, relatively long limbs, and distinctive anterior clypeal margin with three convexities. While most Iridomyrmex species are restricted to Australia and New Guinea, I. anceps occurs more broadly. The species is found in the Old World from India, China and Malaysia through the Philippines and Indonesia, across northern Australia and throughout Melanesia, Micronesia and into Polynesia. It is not known whether I. anceps has increased its range with the assistance of human-mediated dispersal, or if its current range was already established prior to contact with humans. The species is present on Tokelau, which is the easternmost Pacific Island with a native ant fauna, but has not been reported from Hawaii. The species is not considered a significant pest across any of its range.
Malaysia, India, China, Philippines, Indonesia, Australia, Micronesia, Papua New Guinea, Fiji, Tokelau. United Arab Emirates population may be introduced.
The confusion surrounding what part, if any, of the range is introduced is driven by the taxonomic uncertainty of the I. anceps group. Heterick & Shattuck (2011)recently synonymized six names with I. anceps, lumping the group across its entire range into a single species. Arguments for treating the taxa involved instead as a group or complex of species were made by Hoffman et al. (2011). It is the opinion of the authors that a more comprehensive study of the entire group across its entire range, possibly with the aid of molecular tools, is required to answer the question.
Iridomyrmex anceps had long been considered to have established an introduced population in New Zealand (e.g. (Faulds, 1970; Lester, 2005)), but the ants were later confirmed to be a species distantly related to I. anceps (Don, 2007). Iridomyrmex anceps is reported from the United Arab Emirates, but the record is not discussed in either Heterick & Shattuck (2011)or Hoffman et al. (2011). Wilson & Taylor (1967)claimed that the specimen of I. anceps collected at the Nadi airport in Fiji was evidence of the species’ eastward expansion into the Pacific. That claim is obviated, or at least pushed back a half century, by the recent synonymy of I. anceps ignobilis (Mann) which Mann described from Fiji in 1921. The distribution of I. anceps in Fiji is limited to the mostly disturbed habitat on the western (leeward) side of Fiji’s largest island, Viti Levu, suggesting perhaps that it is a relatively recent arrival that has not dispersed to the full extent of its capacity (Sarnat & Economo, In Press). The species was found by Ward (2007)to be aggressive at baits, but such behavior was not observed by the less rigorous observations reported in Sarnat & Economo (In Press). Given the success of I. anceps on Pacific islands, it is somewhat surprising that it has not yet been found in Hawaii.
Diagnosis among workers of introduced and commonly intercepted ants in the United States. Worker caste weakly polymorphic, but lack distinct major caste. Antenna 12-segmented. Antennal scape length less than 1.5x head length. Eyes medium to large (greater than 5 facets); placed at or above midline of face. Eyes do not break outline of head. Antennal sockets and posterior clypeal margin separated by a distance less than the minimum width of antennal scape. Anterior clypeal margin with one median and two lateral rounded projections. Mandible with distinct basal angle. Dorsum of mesosoma lacking a deep and broad concavity, with erect hairs that are thin and flexuous. Promesonotum separated from propodeum by metanotal groove. Propodeum and petiolar node both lacking a pair of short teeth. Propodeum lacking posteriorly projecting protrusion; dorsal surface not distinctly shorter than posterior face. Waist 1-segmented. Petiole upright and not appearing flattened. Gaster armed with ventral slit. Distinct constriction not visible between abdominal segments 3+4. Color uniformly light to dark brown.
Among introduced and commonly intercepted ants in the United States, I. anceps is most likely confused with dolichoderines with upright petiolar nodes and inset eyes that do not break the outline of the head, namely Dolichoderus, Linepithema and Ochetellus species. The low propodeal profile and convex propodeal declivity of I. anceps separates it from Dolichoderus and Ochetellus species. Iridomyrmex anceps is separated from Linepithema species by (1) eyes that are situated at or above the midline of the head; (2) mandibles with distinct basal angles; and (3) anterior clypeal border with one median and two lateral convexities.
Collingwood, C.A., Tigar, B.J. & Agosti, D. (1997) Introduced ants in the United Arab Emirates. J. Arid Environ., 37, 505-512.
Don, W. (2007) Ants of New Zealand. Otago University Press, Dunedin,pp.
Faulds, W. (1970) A second species of Iridomyrmex Mayr established in New Zealand. N. Z. Entomol., 4(4), 18-19.
Heterick, B.E. & Shattuck, S. (2011) Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae). Zootaxa, 2845, 1-174.
Hoffmann, B.D., Andersen, A.N. & Zhang, X. (2011) Taxonomic confusion of two tramp ant species: Iridomyrmex anceps and Ochetellus glaber are really species complexes. Curr. Zool., 57, 662-667.
Lester, P.J. (2005) Determinants for the successful establishment of exotic ants in New Zealand. Diversity Distrib., 11, 279-288.
McGlynn, T.P. (1999) The worldwide transfer of ants: geographical distribution and ecological invasions. J. Biogeogr., 26, 535-548.
Sarnat, E.M. & Economo, E.P. (In Press) Ants of Fiji. Univ. Calif. Publ. Entomol.,
Ward, D.F. (2007) The distribution and ecology of invasive ant species in the Pacific Region. PhD thesis, in Biological Sciences, The University of Auckland, xiii + 173 p.
Wilson, E.O. & Taylor, R.W. (1967) The ants of Polynesia (Hymenoptera: Formicidae). Pac. Insects Monogr., 14, 1-109.
Found most commonly in these habitats: 2 times found in port of entry/city, 12 times found in Rainforest, 10 times found in Savanna, 4 times found in Pandanus & Casaurina forest, 30am on a sunny, sunny day (already!) times found in Didn't see Anoplolepis; PB baiting along trail; Iridomyrmex collected in Savannah area ~8, 1 times found in Botanical garden, 1 times found in peak of limestone pinnacle, scrubby veg., 4 times found in primary forest, 4 times found in Dry sclerophyll, 1 times found in veg seems especially short, savannah, no pandanus immediately nearby; monomorium? nest in dead branch of living tree. Camponotus nest in dead stick on ground at base of same tree; 1 or 2 Tapinoma ne, ...
Found most commonly in these microhabitats: 2 times recruiting to bait, 5 times under rock, 1 times nesting in sand, 1 times along trail; Iridomyrmex collected in Savannah area, 4 times Malaise trap, 1 times veg seems especially short, savannah, no pandanus immediately nearby; monomorium? nest in dead branch of living tree. Camponotus nest in dead stick on ground at base of same tree; 1 or 2 Tapinoma ne, 1 times nest in rocky soil, 3 times sieved litter, 1 times from nest under cement in road, 3 times under stone, 1 times strays ex clay bank Garden, ...
Collected most commonly using these methods: 5 times hand collected|aspirator, 4 times H, 3 times water traps, 9 times flight intercept trap, 7 times traps, 7 times Pitfall trap, 2 times hand collected|aspirator>bait trap|peanut butter, 2 times Hand collection, 6 times Pitfall, 3 times light trap, 5 times M, ...
Elevations: collected from 5 - 1900 meters, 459 meters average
Type specimens: syntype of Iridomyrmex excisus: casent0915581; syntype of Iridomyrmex anceps papuana neocaledonica: casent0905047; syntype of Iridomyrmex anceps watsonii: casent0909501; syntype of Iridomyrmex bicknelli formosae: casent0909507; syntype of Iridomyrmex gracilis papuana: casent0905045; syntype of Iridomyrmex rufoniger metallescens: casent0905055; syntype of ridomyrmex anceps sikkimensis: casent0909500; type of Formica anceps: focol2796, focol2797; type of Iridomyrmex bicknelli r. formosae: focol0171, focol0172, focol0176