Lasius brunneus

This species is widespread in Europe. It lives only where broad-leaved trees occur (Rigato & Toni, 2011).

Identification
Bicoloured with gaster dark brown contrasting with testaceous or pale reddish brown head and alitrunk. Pubescence and body hairs sparse. Occipital hairs restricted to median area of back of head only. Scapes and tibiae never with erect hairs. Back of head flat or feebly concave. Frontal triangle and frontal furrow distinct, ocelli small but always clearly visible. Length: 3.2-4.5 mm (Collingwood 1979).

A distinct species characterized by large males with intermediate sitkaensis-niger type mandibles and workers with short scapes and sparse pilosity. (Wilson 1955)

Distribution
Spain to Crimea and West Himalayas, Italy to Sweden (Collingwood 1979).

Distribution based on Regional Taxon Lists
Oriental Region: India, Pakistan. Palaearctic Region: Albania, Andorra, Armenia, Austria, Belarus, Belgium, Bulgaria, Croatia, Czech Republic, Denmark, Finland, France, Georgia, Germany, Greece, Hungary, Iberian Peninsula, Iran, Israel, Italy, Latvia, Lithuania, Luxembourg, Netherlands, Norway, Poland, Portugal, Republic of Korea, Republic of Macedonia, Republic of Moldova, Romania, Russian Federation, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey, United Kingdom of Great Britain and Northern Ireland.

Biology
Collingwood (1979) - This species nests in the interior of old trees, chiefly oak, but has also been recorded from hedgerows. It is fugitive and non-aggressive, rapidly dispersing on disturbance and because of its cryptic habits may be somewhat under-recorded. In Norway and Sweden it has frequently occurred nesting in the timbers of old houses and farm buildings, where its populous colonies may be difficult to dislodge. It chiefly tends tree aphids including the large bark feeding Stomaphis. Single queens initiate colonies in the crevices of old trees but may also be accepted back into the mother nest after the mating flight which occurs in June and early July.

Wilson (1955) - Most European authors agree that brunneus is a timid species adapted to living under the bark and in the wood of tree trunks. Donisthorpe (1927) found a large population of this species in the Windsor Forest of England limited to living trees, which the ants penetrated from the trunk up into the main branches and down into the roots. Various trees were inhabited, including oaks, elm, ash, beech, poplar and maple. It is not clear whether the workers carried on much excavation in the living wood, but this seems unlikely due to the rather unspectacular mandibular apparatus of the species. Forsslund (1949) found brunneus in oaks in dense, undisturbed woodland in several localities in the vicinity of Stockholm. The nests were mostly in dead wood, but occasional galleries penetrated living wood. Scherdlin (1909) found the species in Alsace nesting in the trunks of trees and timber of houses. Clausen (1938) observed a swarm of reproductives inside a house in Zurich. Gosswald (1932) states that in Germany brunneus is found as often under stones as in dead wood; since this observation is divergent from those of other authors, the possibility must be considered that he was erroneously including some alienus in his concept of brunneus.

Donisthorpe (ibid.), who has undertaken the most careful study of this species to date, found workers transporting and tending aphids of the genus Stomaphis. He also observed them carrying psoeids and other small insects to the nests, presumable for use as animal food.

brunneus appears to hold its nuptial flights earlier in the day and season than other European members of the subgenus. Donisthorpe (ibid.) encountered winged queens and males swarming over the trunk of an oak at noon on June 25, and Forsslund (ibid.) saw the same thing from noon to 1:30 p.m. during the period June 10-16.

Other Insects
This ant has been associated with the butterfly (Obregon et al. 2015).

Nematodes
This species is a host for the nematodes, , , and  (Kohler, 2012).

Nomenclature

 *  brunneus. Formica brunnea Latreille, 1798: 41 (w.q.) FRANCE. Mayr, 1855: 358 (m.); Lorite, Chica & Palomeque, 1998: 28 (k.). Combination in Lasius: Mayr, 1861: 50; in Donisthorpea: Donisthorpe, 1915d: 347; in Formicina: Emery, 1916b: 241; in Lasius: Müller, 1923: 127; in Acanthomyops: Kuznetsov-Ugamsky, 1927e: 188; in Lasius (Lasius): Wilson, 1955a: 47. Subspecies of niger: Forel, 1874: 47; Forel, 1892i: 307; Bondroit, 1910: 486; Kuznetsov-Ugamsky, 1927e: 188. Status as species: André, 1881b: 60; Dalla Torre, 1893: 182; Bondroit, 1912: 352; Forel, 1915d: 52; Bondroit, 1918: 26; Müller, 1923: 127; Karavaiev, 1927c: 279; Finzi, 1930d: 316; Menozzi, 1939a: 313; Wilson, 1955a: 47; Bernard, 1967: 358; Kutter, 1977c: 228; Collingwood, 1982: 285; Atanassov & Dlussky, 1992: 238; Seifert, 1992b: 6. Senior synonym of pallida: Latreille, 1802c: 169; Wilson, 1955a: 47; of timida: Smith, F. 1858b: 7; Seifert, 1992b: 6; of alienobrunneus: Stärcke, 1944a: 157; Wilson, 1955a: 47; Kutter, 1977c: 14; Seifert, 1992b: 6; of nigrobrunneus: Wilson, 1955a: 47; Seifert, 1992b: 6. Current subspecies: nominal plus emarginatobrunneus.
 * pallida. Formica pallida Latreille, 1798: 41 (w.q.) FRANCE. Junior synonym of brunneus: Latreille, 1802c: 169. Unrecognisable taxon, incertae sedis in Lasius: Seifert, 1992b: 48. [Note. As the taxa brunneus and pallida were both described by Latreille and the synonymy was also established by Latreille, it seems reasonable to let it stand.]
 * timida. Formica timida Foerster, 1850a: 35 (w.) GERMANY. Schenck, 1852: 54 (q.m.). Junior synonym of brunneus: Smith, F. 1858b: 7; Seifert, 1992b: 6.
 * alienobrunneus. Lasius niger var. alienobrunneus Forel, 1874: 47 (w.) SWITZERLAND . Emery, 1916b: 249 (q.). Junior synonym of alienus: Dalla Torre, 1893: 182. Revived from synonymy as subspecies of brunneus: Ruzsky, 1902d: 17. Raised to species: Bingham, 1903: 340. Subspecies of brunneus: Forel, 1915d: 53; Karavaiev, 1927c: 279. Junior synonym of brunneus: Stärcke, 1944a: 157; Wilson, 1955a: 47; Kutter, 1977c: 14; Seifert, 1992b: 6.
 * nigrobrunneus. Acanthomyops (Dendrolasius) brunneus var. nigrobrunneus Donisthorpe, 1926b: 18 (w.) ITALY. Junior synonym of brunneus: Wilson, 1955a: 47.

Worker
Wilson (1955) - (1) Scape shorter relative to head width than in any other member of the subgenus; S1 82-91 in all European series measured; 94 in the himalayanus lectotype and in one specimen from Lahore, Pakistan, both small specimens.

(2) Small individuals (PW 0.50-0.57 mm.), when viewed in perfect full face, with the lateral margins of the eyes not reaching the lateral borders of the head; in Lasius niger and Lasius alienus they reach or exceed it.

(3) Mandibles proportionately shorter, more incurved, and inserted slightly closer to the midline, and head more massive relative to the alitrunk, than other Lasius s. s. (Pl. 1, Fig. 9). Occipital margin viewed in full face flat to feebly convex, as opposed to the typically concave outline of niger and alienus.

(4) Mandible with only two basal teeth in all of seven nest series examined for this character.

(5) Scapes and tibiae completely devoid of standing hairs and nearly devoid of hairs of any inclination. Body pilosity sparse; the curving portion of the occipital angles viewed in full face typically devoid of hairs, rarely with one or two; the latter condition occurs in other members of the subgenus but is highly exceptional.

(6) Alitrunk and petiole homogeneous light reddish brown, rarely medium reddish brown, contrasting against the dark brown gaster. The head usually the same color, occasionally darkening to medium or dark reddish brown to contrast against the alitrunk. (niger and alienus typically concolorous.)

Size range and dispersion probably about the same as in niger. In a sample of 29, with no more than 2 individuals per nest series, PW range 0.50-0.73 mm., mean with standard error 0.630 ± 0.012 mm., standard deviation 0.063 mm. ML less than EW. Anterior margin of median clypeal lobe and structure of the mandibular basal angle essentially as in the niger complex. The greater massiveness of the alitrunk in this species can perhaps best be expressed as a ratio of alitrunk length to the maximum head depth measured perpendicular to the long axis of the head. Several medium-sized brunneus gave such a ratio of 67-69, whereas alienus of comparable size ranged between 70 and 76. Viewed from the side the propodeal angle tends to be more acute and the declivitous face of the propodeum tends to be longer relative to the dorsal face than in other Lasius s. s. The dorsal margin of the petiole was invariably concave in all series examined; occasionally the concavity is so deep as to be nearly semicircular.

Queen
Wilson (1955) - (1) SI low; 68-71 in 9 individuals from 6 localities having HW 1.49-1.64 mm., and 76 in a smaller individual with HW 1.39 mm,

(2) Pilosity and mandibular dentition as in worker.

(3) Frontal suture well marked, set in the middle of a conspicuous broad, shallow trough.

(4) Color distinctive; body uniformly dark reddish brown, appendages a contrasting yellowish brown.

(5) Fore wings infumated in the inner and upper thirds.

Male
Wilson (1955) - (1) Larger than other members of the subgenus, HW 1.04-1.10 mm.

(2) Mandibles of a type intermediate between Lasius pallitarsis and Lasius niger: there is a well marked subapical cleft as in sitkaensis, but it is set more posteriorly than in this primitive species; the basal angle is broadly rounded and the masticatory border lacks denticles, both of which characters are associated with the more advanced niger type.

(3) Frontal suture conspicuous as in queen.

(4) The entire dorsal petiolar margin involved in a deep concavity. In a series from Windsor Forest, Berks, England, secondary lateral convexities are present within this concavity.

(5) Parameres shorter relative to HW than in other members of the subgenus.

SI of several individuals measured 60-64, overlapping part of range of variation of niger (q. v.). ML 0.15-0.17 mm., overlapping part of ranges of niger and emarqinatus.