Lasius bicornis

Identification
A rare Eurasian species somewhat similar in habitus to North American species Lasius minutus but showing profound differences in the petiolar outline and pilosity. (Wilson 1955)

Worker clear citron yellow. Funiculus segments not longer than broad; scape distinctly flattened. Outline of petiole characteristic: high, tapering dorsally with a deep emargination. Body hairs long, longest hairs nearly as long as maximum hind tibial width, sparse on dorsum of gaster where restricted to posterior borders of tergites; genal hairs sparse, scapes and tibiae bare. Length: 4.0-4.5 mm (Collingwood 1979).

Distribution
Central and South Europe from Pyrenees and Caucasus but also recorded from Himalayas (Kashmir), South Italy to Netherlands; uncommon (Collingwood 1979).

Distribution based on Regional Taxon Lists
Oriental Region: India. Palaearctic Region: Armenia, Austria, Belgium, Bulgaria, Croatia, Czech Republic, France, Georgia, Germany, Greece, Hungary, Iberian Peninsula, Italy, Poland, Slovenia, Spain.

Biology
This species nests in rotten logs. Alatae have been taken in September (Poldi, 1962).

Nomenclature

 *  bicornis. Formica bicornis Foerster, 1850a: 41 (q.) GERMANY. Forel, 1874: 47 (w.); Forel, 1915d: 56 (m.). Combination in Lasius: Mayr, 1861: 51; in Formicina: Emery, 1916b: 242; Menozzi, 1918: 87; in Acanthomyops: Ruzsky, 1925b: 45; in Lasius (Chthonolasius): Ruzsky, 1914a: 61; Emery, 1925b: 232; Wilson, 1955a: 183. Subspecies of umbratus: Forel, 1874: 47; Emery & Forel, 1879: 453; Mayr, 1886d: 430; Forel, 1886f: 208; Forel, 1904b: 387; Bondroit, 1910: 485. Status as species: André, 1882b: 196; Ruzsky, 1902d: 15; Bondroit, 1912: 352; Emery, 1916b: 242; Bondroit, 1918: 34; Emery, 1922b: 13; Karavaiev, 1927c: 279; Stärcke, 1937: 55; Stitz, 1939: 302; Wilson, 1955a: 183; Bernard, 1967: 365; Kutter, 1977c: 231; Collingwood, 1982: 293; Seifert, 1988: 161; Atanassov & Dlussky, 1992: 251. Senior synonym of incisa: Smith, F. 1858b: 8; Emery, 1922b: 13; Seifert, 1988: 161; of microgyna: Vandel, 1926: 197; Wilson, 1955a: 183; of kashmirensis, neapolitana, oertzeni: Wilson, 1955a: 183.
 * incisa. Formica incisa Schenck, 1852: 63 (w.) GERMANY. Junior synonym of bicornis: Smith, F. 1858b: 8; Emery, 1922b: 13; Seifert, 1988: 161.
 * oertzeni. Lasius bicornis subsp. oertzeni Forel, 1910a: 26 (w.q.m.) GREECE. Combination in L. (Chthonolasius): Emery, 1925b: 233. Raised to species: Stärcke, 1937: 56. Junior synonym of bicornis: Wilson, 1955a: 183.
 * microgyna. Formicina microgyna Bondroit, 1918: 33, figs. 16, 17 (q.m.) FRANCE. Combination in Lasius (Chthonolasius): Emery, 1925b: 233. Subspecies of bicornis: Emery, 1925b: 233; Stärcke, 1937: 56. Junior synonym of bicornis: Vandel, 1926: 197; Wilson, 1955a: 183.
 * neapolitana. Lasius bicornis var. neapolitana Emery, 1922b: 13 (q.) ITALY. Junior synonym of bicornis: Wilson, 1955a: 183.
 * kashmirensis. Acanthomyops (Chthonolasius) bicornis subsp. kashmirensis Donisthorpe, 1930a: 225 (q.m.) INDIA. Junior synonym of bicornis: Wilson, 1955a: 183.

Worker
Wilson (1955) – Based on a single oertzeni syntype and an unlabeled worker in the Mayr Collection.

(1) PW of oertzeni syntype 0.68 mm., Mayr specimen 0.79 mm., well within range of Lasius umbratus size variation.

(2) Body hair longer than in umbratus-rabaudi but shorter and finer than in minutus. In both available specimens the dorsal gastric hairs average about 0.09 mm, and do not exceed 0.14 mm,; the maximum width of the hind tibia at its midlength commonly used in the present study as a reference measurement, is 0.16 mm, The cephalic and gastric hairs of these specimens are sparser than in minutus. The number of hairs extending beyond the profile of the first gastric segment anterior to the extreme posterior strip and seen in perfect side view is 17 in the oertzeni syntype and only 6 in the Mayr specimen; 30 or more is usual for minutus, umbratus-rabaudi, and subumbratus.

(3) Petiolar outline in the oertzeni syntype similar to that described for the queen (Pl. 2, Fig. 3); emargination somewhat more shallow in the Mayr specimen.

(4) Scape flattened to the extent seen in extreme rabaudi workers. oertzeni syntype: maximum width at scape midlength 0.11 mm., minimum width 0.06 mm. Mayr specimen; maximum width 0.12 mm., minimum width 0.07 mm.

Queen
Wilson (1955) - (1) Smaller than umbratus but considerably larger than minutus. HW of oertzeni lectotype 1.34 mm.; microgyna lectotype 1.25 mm., syntopotypes 1.24 and 1.26 mm., Saint Sever "syntypes" 1.22 and 1.29 mm. ; a queen from the Taurus Mountains, Turkey (Berlin Museum), 1.34 mm. (measured by H. Bischoff).

(2) Long standing hairs abundant over the alitrunk, approaching the minutus condition, but sparser on the head and gastric tergites. In full face, the number of hairs projecting beyond the occipital contour is 4 in the oertzeni lectotype, 6 in the microgyna lectotype, 5 and 7 in the microgyna syntopotypes, and 6 and 7 in the Saint Sever specimens; the number in minutus is commonly 30 or more. In perfect side view, the first gastric tergite of the oertzeni lectotype shows only 15 standing hairs projecting beyond its profile, the microgyna lectotype 12, and microgyna syntopotypes 10 and 14, the St. Sever specimens 13 and 15, and a specimen from Hanau (Berlin Museum) 7; the typical number for minutus is 25 or more. In bicornis the pilosity of the first gastric tergite is limited mostly to the anterior slope and extreme posterior strip; in minutus it is evenly distributed over all of the tergital surface except for the anteriormost part of the anterior slope. The body hairs are proportionately shorter than in minutus. The longest hairs of the first and second gastric segments shorter than the maximum width of the hind tibia at its midlength (in the oertzeni lectotype, for instance, maximum hair length is 0.17 mm., tibia width is 0.21 mm.). At the same time, bicornis resembles minutus in having the scapes and legs completely bare of hairs except for a few scattered along the flexor margins of the femora.

(3) The petiole in frontal view slender, tapering dorsally; deeply emarginate, so that the depth of the emargination measured from the level of the bicornuate dorsal crest to the bottom of the emargination is distinctly greater than the width of the emargination taken across the midpoint of the depth measurement (Pl. 2, Fig. 2).

(4) Scapes flattened as in rabaudi; in the oertzeni lectotype, the maximum width at the midpoint is 0.14 mm., the minimum width only 0.07 mm. .At the same time, the funicular segments are not elongated as in rabaudi; third funicular segment length in oertzeni lectotype 0.11 mm., width 0.10 mm.

(5) As in minutus, the mandibles more massive relative to the remainder of the head and set farther apart from the midline when compared with umbratus.

Type Material
Wilson (1955) - HOLOTYPE. Dr. Bischoff has informed me that the unique type of bicornis is not with the Foerster Collection in the Berlin Museum, and it has not been found among the Foerster material in the Mayr Collection. Fortunately, the original description adequately covers the essential diagnostic features in petiole shape and pilosity of this distinctive species, and there can be little doubt that the name has been correctly applied in the present study.