Tetramorium simillimum

A tramp species that has developed a pantropical distribution and is even found in temperature areas, albeit in protected areas such as heated greenhouses.

Identification
A member of the Tetramorium simillimum species group.

Very similar to Tetramorium caldarium, as detailed in the identification section of this other species.

Weakly sculptured, pale red much smaller than Tetramorium guineense. Length: 1.6-2 mm (Collingwood 1979).

Bolton (1977) - T. simillimum is a small, quite common pantropical tramp species of African origin which is also found as an introduction in hothouses and zoological gardens in the temperate zone. A number of related species are known from the Ethiopian region but none of these occurs outside Africa. The distinctive sculpture and short, stout pilosity will differentiate simillimum from other species in the Oriental and Indo-Australian regions.

Bolton (1980) - Within the group T. simillimum is closest to Tetramorium delagoense, Tetramorium bothae and Tetramorium rhetidum, sharing the characters of strongly developed scrobes and frontal carinae and dense ground-sculpture. Its separation from these species is discussed under their respective descriptions.

Tetramorium simillimum is not a particularly variable species but West African populations tend to have the head at the lower end of the width-range given above, giving them a relatively high CI. There is also a tendency in these forms to develop a gaster which is distinctly darker in colour than the head and alitrunk.

Distribution based on Regional Taxon Lists
Afrotropical Region: Cameroun, Comoros, Eritrea, Ethiopia, Guinea, Ivory Coast, Kenya, Malawi, Mozambique, Socotra Archipelago, Uganda, United Republic of Tanzania, Yemen, Zambia. Australasian Region: Australia, New Caledonia, Norfolk Island. Indo-Australian Region: Borneo, Cook Islands, Fiji, Guam, Hawaii, Indonesia, Kiribati, Krakatau Islands, Malaysia, Marshall Islands, Micronesia (Federated States of), New Guinea, Niue, Northern Mariana Islands, Palau, Philippines, Samoa, Solomon Islands, Tokelau, Tonga, Vanuatu, Wallis and Futuna Islands. Malagasy Region: Madagascar, Mauritius, Mayotte, Réunion, Seychelles. Nearctic Region: Canada, United States. Neotropical Region: Barbados, Bermuda, Brazil, Costa Rica, Cuba, Dominican Republic, Ecuador, Galapagos Islands, Greater Antilles, Grenada, Guadeloupe, Haiti, Mexico, Paraguay, Puerto Rico. Oriental Region: Bangladesh, India, Sri Lanka, Thailand. Palaearctic Region: China, Denmark, Estonia, Israel, Japan, United Kingdom of Great Britain and Northern Ireland.

Australia
The range for Tetramorium simillimum given by Brown and Taylor (1985) is probably understated. Unlike some other exotic myrmicines in Australia, this species does not seem to adversely affect the native ant fauna.

Bahamas
Wheeler (1905) - This tropicopolitan species is common in certain localities near settlements both on Andros and New Providence. At Nicholl's Town, on the eastern coast of the former island, I found it in and under rotting coconut boles that had been prostrated some years ago by a hurricane. These nests contained many males and winged females (May 14). On New Providence the species was common under stones in the Queen's Staircase in Nassau, in the Menendez Sisal Plantation near Stanley, and in the dwindling 'pine yards' near the Blue Hills.

Europe
Collingwood (1979) - This cosmopolitan species occasionally occurs in heated glasshouses in Europe and has been recorded from Denmark and also on several occasions in England.

Puerto Rico
Wheeler (1908) - In Culebra a few colonies were found nesting under stones and logs on the beach, in Coamo Springs several colonies were seen under stones in the creek bottom near the baths.

Florida USA
A common species found as far north as St. Johns County, Florida. Nests are usually in soil in open areas, often around buildings or parking lots. Pest status: none. First published Florida record: Wheeler 1932. (Deyrup, Davis & Cover, 2000.)

Socotra, Yemen
Sharaf et al. (2017) - Workers of this species were found foraging on the soil under thrown, dry, date palm fronds. Several workers were found foraging on the ground under grasses.

Nomenclature

 *  simillimum. Myrmica simillima Smith, F. 1851: 118 (w.) GREAT BRITAIN. Meinert, 1861: 331 (gynandromorph); André, 1883a: 289 (q.m.); Imai, Baroni Urbani, et al. 1984: 8 (k.). Combination in Tetramorium: Mayr, 1861: 61. Senior synonym of pygmaeum: Forel, 1916: 421; of brevispinosa: Borgmeier, 1937b: 241; of insulare: Yarrow, 1967: 28; of denticulatum, opacior, parallela: Bolton, 1977: 131; of bantouana, exoleta and material of the unavailable name breve referred here: Bolton, 1980: 320. See also: Emery, 1909d: 696.
 * parallela. Myrmica parallela Smith, F. 1859a: 147 (w.) INDONESIA (Aru I.). Combination in Tetramorium: Donisthorpe, 1932c: 455. Junior synonym of simillimum: Bolton, 1977: 131.
 * pygmaeum. Tetramorium pygmaeum Emery, 1877b: 371 (q.) ETHIOPIA. Emery, 1901e: 62 (m.); Emery, 1915g: 17 (w.). Junior synonym of simillimum: Forel, 1916: 421.
 * denticulatum. Tetramorium simillimum r. denticulatum Forel, 1902c: 235 (w.) INDIA. Junior synonym of simillimum: Bolton, 1977: 131.
 * bantouana. Tetramorium pusillum var. bantouana Santschi, 1910c: 382, fig. 10 (w.q.m.) CONGO. Junior synonym of simillimum: Bolton, 1980: 320.
 * opacior. Tetramorium simillimum var. opacior Forel, 1913k: 81 (w.) SRI LANKA. Junior synonym of simillimum: Bolton, 1977: 131.
 * exoleta. Tetramorium pusillum var. exoleta Santschi, 1914d: 366 (w.) NIGERIA. Junior synonym of simillimum: Bolton, 1980: 320.
 * brevispinosa. Wasmannia auropunctata subsp. brevispinosa Borgmeier, 1928a: 36, figs. 4, 5 (w.) BRAZIL. [Unresolved junior secondary homonym of brevispinosus Stitz, above.] Junior synonym of simillimum: Borgmeier, 1937b: 241.
 * insulare. Tetramorium simillimum var. insulare Santschi, 1928c: 69 (w.) FIJI IS. [Unresolved junior secondary homonym of insularis Menozzi, above.] Junior synonym of simillimum: Yarrow, 1967: 28; Bolton, 1977: 131.

Type Material
Bolton (1977) - Syntype workers, Great Britain: England, Dorset (types lost, presumed destroyed). although the types of this species have almost certainly been lost or destroyed at some time in the past (they are not in Smith's material at, nor are they at UM, Oxford), the identity of the species does not appear to have ever been in doubt. It is this traditional interpretation which I take as my basis for defining simillimum, and as the species is very widespread and quite well known I can see no obvious reason for designating a neotype.



Myrmica parallela

Holotype worker in. Specimen without locality label, but with a label “simillima” in Smith’s writing. Type-locality “Aru” according to original description.

Wetterer and Hita Garcia (2015) - The species Tetramorium caldarium was described by Roger (1857) from Poland, with the specimens collected from a greenhouse growing pineapples. This species was promptly (Roger 1862) synonymized under T. simillimum, where it remained until 1979 when Bolton revived its status as a valid species. Museum specimens of T. simillimum that do not have contemporary identifications should be examined to be sure they are not T. caldarium (see the identification section of this other species for diagnostic characters).

Worker
(length3/4 - 1 line). Head and thorax pale ferruginous, the legs and antennae more pallid, the coxae a little coloured, the eyes black; the abdomen is rufo-fuscous, pale towards the apex; the head is evenly longitudinally striate; the thorax above is without the usual transverse suture, but is a little compressed at the sides about the middle, and gradually slightly narrowed from the prothorax towards the nodes of the peduncle; the metathorax is truncate at the apex, and the spines are short, broad, and acute; the abdomen is furnished with a few scattered erect hairs.

Bolton (1977) - TL 2.1-2.5, HL 0.54-0.60, HW 0.48-0.54, CI 88-93, SL 0.36-0.42, SI 74-80, PW 0.34-0.40, AL 0.58-0.68 (45 measured).

Mandibles finely and usually weakly sculptured, appearing usually as feeble striation or weak shagreening but sometimes more or less dully shining with only superficial sculpture. Anterior clypeal margin entire. Frontal carinae distinct, extending back almost to the occiput and very shallowly, evenly convex along their length. Antennal scrobes broad and quite shallow, but distinct. Eyes moderate in size, maximum diameter c. 0.11-0.14, about 0.22-0.26 x HW. Occipital margin in full-face view broadly and shallowly concave, the sides of the head behind the eyes sometimes roughly parallel but usually weakly convex; occipital corners evenly rounded. Propodeum armed with a pair of short, triangular acute teeth which are usually shorter than the metapleural lobes, rarely very slightly longer. Metapleural lobes broad, roughly triangular in shape. Petiole in profile with a stout anterior peduncle, the outline shape of the node as shown in figure, but in some populations the node tending to narrow very slightly from base to apex. In dorsal view the node always slightly broader than long, somewhat variable in shape but always broadened posteriorly before narrowing to the postpetiolar junction. Dorsum of head finely and quite densely longitudinally rugulose, the spaces between the rugulae filled with a fine, dense conspicuous reticulate-punctulation or granulation. Area of antennal scrobes densely and finely reticulate-punctulate. Dorsal alitrunk finely, often faintly longitudinally rugulose, with traces of reticulation on pronotum, the spaces between the rugulae densely punctulate. Dorsal petiole and postpetiole similarly but less strongly sculptured, the sculpture sometimes reduced but never completely absent, always with traces of punctulation and nearly always with traces of faint rugulation. Sides of alitrunk densely and conspicuously reticulate-punctate. Gaster unsculptured. All dorsal surfaces of head and body with scattered short hairs, generally longer on the gaster than elsewhere. Hairs on ali trunk conspicuous, short, stout and blunt. Antennal scapes and dorsal (outer) surfaces of hind tibiae only with very short, fine, appressed pubescence. Colour yellow to yellowish brown, usually with the gaster darker brown but some populations uniformly coloured.

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