Lasius rabaudi

This species exhibits temporary social parasitism. Queens found new colonies by infiltrating an established nest of Lasius niger, killing the queen and using host workers to care for her initial brood.

Identification
A common Palaearctic species very close to Lasius umbratus and safely distinguishable only in the queen caste.

Distribution based on Regional Taxon Lists
Palaearctic Region: Afghanistan, Denmark, France, Georgia, Iberian Peninsula, Morocco, Poland, Slovakia, Spain, Turkey.

Biology
Starcke has suggested, based on observational evidence, that rabaudi can serve in turn as the host for Lasius fuliginosus.

Nomenclature

 *  rabaudi. Formicina rabaudi Bondroit, 1917a: 177, fig. 2 (q.) FRANCE.
 * Emery, 1924c: 170 (w.); Wilson, 1955a: 169 (m.).
 * Combination in Lasius (Chthonolasius): Emery, 1925b: 233.
 * Junior synonym of umbratus: Bourne, 1973: 25; van Boven, 1977: 151.
 * Status as species: Bondroit, 1918: 35; Bondroit, 1920a: 144; Wilson, 1955a: 168 (redescription); Bernard, 1967: 364 (redescription); Baroni Urbani, 1971c: 212; Kutter, 1977c: 234; Azuma, 1977: 117; Arnol'di & Dlussky, 1978: 555 (in key); Collingwood, 1978: 89 (in key); Yamauchi, 1979: 169; Agosti & Collingwood, 1987b: 281 (in key); Seifert, 1988a: 159 (redescription); Seifert, 1990: 11; Bolton, 1995b: 225.

Worker
Wilson (1955) - (1) The most reliable queen character, the flattening of the scape, seems to be reflected in the worker, but there is considerable overlap between the two species, and probably a majority of worker series unaccompanied by queens cannot be certainly placed. Series of Lasius umbratus accompanied by queens are characterized as follows: in workers with maximum midpoint scape width of 0.10-0.12 mm., the minimum midpoint width was always 0.08 mm. or more. In the two series of Lasius rabaudi accompanied by queens ("Morogi-Mura" and Roermond) the minimum width was distinctly less than 0.08 mm. However, other series unaccompanied by queens, and therefore not determinable by reference to the rabaudi type, completely overlapped determined umbratus and extended far below the identified rabaudi series, to minimum width 0.06 mm.

(2) The "Morogi-Mura" and Roermond series and others with greatly flattened scapes also had abundant standing hairs on the scapes, which character is frequent in umbratus only in northern Eurasian samples.

Queen
Wilson (1955) - (1) Scapes and tibiae conspicuously flattened, so that the minimum width of the 'scape at the midpoint is 0.10 mm. or less (Fig. 15).

(2) Funicular segments tending to be proportionately longer than in umbratus. In the rabaudi series examined, funicular segment III varied 1.47-1.87 X longer than broad, while an equivalent sample of Eurasian umbratus varied 1.00-1.50 X longer than broad, with only one specimen exceeding the rabaudi minimum of 1.47 X.

(3) The shape of the petiole characteristic, and less variable than in umbratus: in frontal view subquadrate, nearly as broad at the dorsal crest as at the level just above the frontal foramen, and with a rounded to angulate dorsal emargination. European series have concave to straight lateral margins; Japanese series may have convex margins in addition.

Male
Wilson (1955) - Males associated with very flat-scaped workers from Roermond are rather small compared to umbratus (HW about 0.98 mm.) and show certain expected allometric differences in mandibular and petiolar structure, but in this and every other character they are within the extreme range of variation of umbratus. There is no appreciable flattening of the scapes.

Type Material
Wilson (1955) - HOLOTYPE. An alate queen in the Bondroit Collection.