Lasius

Collingwood, C. A., 1979, The Formicidae (Hymenoptera) of Fennoscandia and Denmark., Fauna Entomologica Scandinavica 8, pp. 1-174 : 92-96

Genus Lasius Fabricius, 1804

Lasius Fabricius, 1804:415.

Type-species: Formica nigra Linne , 1758.

The antennae are 12 segmented in the worker and female, 13 segmented in the male. The antennal insertions are situated at the posterior margin of the clypeus and segments2 to 5 are not longer than the succeeding segments. Maxillary palps are 6 segmented, labial palps 4 segmented. The head of the worker caste is somewhat cordate with a posterior emargination in some species. The clypeus is broad and rounded anteriorly. The frontal carinae are short and sub-parallel and in most species the frontal triangle is indistinctly defined. The orifice of the propodeal spiracle is circular or broadly oval situated close to the posterior propodeal border. Ocelli are minute or indistinct in the worker but distinct in the female and male. The petiole is vertical and scale-like in most species.

This genus contains about 42 species with a holarctic distribution. It was extensively revised by Wilson (1955). Members of this genus are predominantly aphidicolous but also carnivorous and scavenging. There are 14 species in Europe of which IO are known to occur in Fennoscandia.

Keys to species of Lasius

Workers

1 Colour shining black; head large, broadly cordate with a distinct posterior emargination (Fig. 137)............................................... 37. fuliginosus (Latreille)

Colour greyish or brownish black or yellow..................................................... 2

2(1) Colour yellow to brownish yellow; maximum eye length 1/4, head width or less ... 3

Colour brownish or greyish black or somewhat bicoloured reddish and black; maximum eye length more than head width ................................................ 8

3 (2) Petiole nodal with dorsal crest in front view strongly convex; head emarginatc posteriorly; with genal margins rounding in towards close set mandibular insertions(Figs. 153,155)....................................................... 42. carniolicus (Mayr)

Petiole with thin dorsal crest, straight or emarginate in front view; back of head convex and genal margins not pronouncedly sloping in towards mandibular insertions which are wide set.......................................................................... 4

4 (3) Front tibiae and antennal scapes with sub-erect hairs standing out clearly from general pubescence....................................................................................... 5

Front tibiae and antennal scapes with pubescence only.................................... 6

5 (4) Scapes and tibiae flattened with thin front edge; petiole scale narrowly rec- tangular.................................................................. 39. meridionalis (Bondroit)

Scapes and tibiae rounded elliptical in cross section; petiole scale with curving sides and more or less emarginate dorsal border........... 38. umbratus (Nylander)

6 (4) Body hairs short, erect hairs on first gaster tergite x 0.3 or less hind tibial width (Fig. 149)....................................................................... 41. mixtus (Nylander)

Body hairs long, erect hairs on first gaster tergite x 0.7 or more hind tibial width............................................................................................................ 7

7 (6) Petiole narrow with deep semicircular emargination; erect hairs on gaster restricted to hind borders of tergites (Fig. 147)................... 40. bicornis (Forster)

Petiole broad with dorsal crest widely emarginate or straight; erect hairs arise all over dorsum of gaster (Fig. 124)................................... 33. flavus (Fabricius)

8 (2) Front tibiae and antennal scapes with abundant semi-erect hairs 36. niger (Linne)

Front tibiae and scapes bare (or with occasional oblique hairs standing out from general pubescence)...................................................................................... 9

9 (8) Body bicoloured with head and alitrunk pale brownish red contrasting with darker gaster; occipital corners without projecting hairs; ocelli usually visible and frontal furrow clearly demarcated (Fig. 131)............ 35. brunneus (Latreille)

Body evenly brownish or greyish black; occipital corners with projecting hairs; ocelli not visible and frontal furrow usually indistinct (Fig. 130) 34. alienus (Forster)

Queens

1 Colour shining black; orifice of metapleural gland without guard hairs; head broadly emarginate and wider than alitrunk; scutum overhangs the pronotal convexity (Fig. 136).................................................... 37. fuliginosus (Latreille)

Colour various from yellowish brown to brownish or greyish black; orifice of metapleural gland with guard hairs; pronotal convexity not covered by scutum:

2 (1) Front tibiae and antennal scapes with standing hairs........................................ 3

Front tibiae and scapes with pubescence but no standing hairs......................... 5

3 (2) Head distinctly narrower than alitrunk at its widest point; eyes without short hairs between facets; colour greyish black .............................. 36. niger (Linne)

Head broader than alitrunk; eyes with short hairs; body colour yellowish brown to brownish black ............................................................................... 4

4 (3) Antennal scapes and tibiae flattened with thin front edge: minimum hind tibial width x 0.5-0.6 maximum width. Petiole scale rectangular in front view; funiculus segments distinctly elongate; sculpture fine and pubescence thin so that general appearance, especially frons, shining; colour brownish black (Figs. 144, 145)........................................................ 39. meridionalis (Bondroit)

Antennal scapes and tibiae oval: minimum hind tibial width x 0.75 maximum width. Petiole scale with rounded sides; hexagonal in frontal view, with distinctly emarginate dorsal crest; sculpture and pubescence somewhat coarse so that general appearance somewhat dull; colour yellowish brown to dark mahogany brown (Figs. 140,141)................................................. 38. umbratus (Nylander)

5 (2) Eyes without short hairs between facets, or one or two at most.........................6

Eyes with numerous short hairs...................................................................... 7

6 (5) Body colour greyish black; head distinctly narrower than alitrunk; frontal triangle usually indistinct; wings clear, not infuscated .......... 34. alienus (Forster)

Body colour brownish black: head more massive, nearly as broad as maximum width of alitrunk; median furrow and frontal triangle always clearly demarcated; wings infuscated basally...................................... 35. brunneus (Latreille)

7 (5) Head distinctly narrower than alitrunk ............................. 33. flavus (Fabricius)

Head as broad or broader than alitrunk .......................................................... 8

8 (7) Petiole very convex in front view; head with rounded occipital lobes and convex genal margins................................................................. 42. carniolicus (Mayr)

Petiole with thin scale-like dorsal crest; back of head straight or weakly concave; genal margins straight or very slightly convex.................................................. 9

9 (8) Gaster with short hairs only, x 0.3 maximum tibial width or less; scale weakly emarginate; size larger -length: 6.0-7.5 mm..................... 41. mixtus (Nylander)

Gaster with long hairs, as long as tibial width; scale deeply incised; size smaller - length: 4.5-5.5 mm ......................................................... 40. bicornis (Forster)

Males

1 Suberect hairs present on either extensor tibial surface or antennal scapes or both ......................................................................................................... 2

Tibiae and scapes with pubescence only ......................................................... 4

2 (1) Mandibles with apical tooth only, masticatory border smoothly rounded into pre-apical cleft; head distinctly narrower than alitrunk ............ 36. niger (Linne)

Masticatory border with distinct teeth; head massive relative to alitrunk, as wide or wider................................................................................................ 3

3 (2) Frons shining with fine microsculpture and thin pubescence; frontal groove and frontal triangle well marked; mandibles with very well defined teeth; body colour evenly black; cross vein m-cu frequently absent on fore-wing (Fig. 146) 39. meridionalis (Bondroit)

Frons somewhat dull with coarse microsculpture and thick pubescence; frontal groove and triangle often indistinctly defined or obscured by pubescence; denticles less sharply defined; body colour brown to brownish black; cross vein m-cu usually present (Fig. 142)............................. 38. umbratus (Nylander)

4(1) Mandibles with a single apical tooth............................................................... 5

Mandibles with a distinct pre-apical tooth or denticles as well as an apical tooth 7

5 (4) Shining black; head large; distinctly emarginate posteriorly; metapleural gland lacking guard hairs (Fig. 138) ...................................... 37. fuliginosus (Latreille)

Colour grey to brownish black; head border convex or straight; metapleural gland with guard hairs ................................................................................... 6

6 (5) Projecting hairs absent on occipital corners of head; pre-apical cleft of man- dible clear, wings fuscous on basal half (Fig. 132)............ 35. brunneus (Latreille)

Head above eyes fringed with projecting hairs; pre-apical cleft of mandibles shallow; basal angle of mandible broadly rounding into edentate masticatory border; wings clear............................................................ 34. alienus (Forster)

7 (4) Petiole thickened in side view, with broadly rounded dorsal crest; back of head with numerous projecting hairs (Fig. 154)......................... 42. carniolicus (Mayr)

Petiole thin in side view, with emarginate or flat dorsal crest; back of head with occasional hairs only.............................................................................. 8

8 (7) Head width less than maximum alitrunk width; mandibles with apical and one pre-apical tooth only; cross vein m-cu often absent on one or both fore wings (Fig. 127)........................................................................ 33. flavus (Fabricius)

Head width as wide as alitrunk; mandibles either denticulate evenly or with at least one or more denticles in addition to apical and pre-apical teeth; cross vein m-cu normally present............................................................................ 9

9 (8) Petiole scale high, narrow, and deeply incised; masticatory border with well defined denticles; size small - length: 3.2 mm.................... 40. bicornis (Forster)

Petiole scale broad, with straight or slightly emarginate dorsal crest; masticatory border with one or two denticles only, the rest obscure or absent; larger length: 3.7-4.5 mm (Fig. 152)........................................ 41. mixtus (Nylander)