Leptothorax

Genus Leptothorax Mayr, 1855

Leptothorax Mayr, 1855:431.

Type-species: Formica acervorum Fabricius, 1793.

North European species small, worker length 2.3-4 mm. Body hairs clavate, not pointed; pronotum rounded anterolaterally; propodeal spines distinct; antennae 11 or 12 segmented in female castes, with 3 segmented club as long as rest of funiculus. Male has 12 or 13 antennal segments. Mandibles distinctly 5-toothed. Notauli very distinct.

In Europe, there are at least 40 species distinguishable on rather slight characters and their taxonomy is in need of revision. Seven species occur in Scandinavia. The North European species live in small communities of 30 up to 300 individuals under stones, in rock crevices, under bark, in twigs or in peat.

Keys to species of Leptothorax

Workers

1 Robust species with It segmented antennae and very distinct mesopropodeal furrow.......................................................................................................... 2

More slender species with 12 segmented antennae.......................................... 3

2(1) Tibiae and scapes with numerous suberect hairs, antennal club dark brown to nearly black, size larger, 3.2-4 mm (Fig. 92)................ 17. acervorum (Fabricius)

Tibiae and scapes with occasional adherent hairs only, antennal club yellow brown to brown, size smaller, 2.5-3.5 mm (Fig. 93)...... 18. muscorum (Nylander)

3(1) Antennal clubs pale, concolorous with rest of antenna, distinct mesopropodeal furrow, propodeal spines long and stout (Fig. 96)............. 19. nylanderi (Forster)

Antennal clubs brown to black, no mesopropodeal furrow............................... 4

4 (3) Propodeal spines reduced to very short broad denticles, petiole outline a blunt triangle in profile, antennal clubs pale brown...................20. corticalis (Schenck)

Propodeal spines distinct, antennal clubs brown to black, distinctly darker than rest of funiculus............................................................................................ 5

5 (4) Propodeal spines long and curved, petiole in profile sharply angled with anterior face rising steeply to anterodorsal ridge; gaster usually with dark band more or less interrupted in middle and front corners of head blackish (Fig.98) 21. interruptus (Schenck)

Propodeal spines short; petiole with a short truncate dorsal area; dark patches on head and gaster not interrupted medially.................................................... 6

6 (5) Dorsal outline of alitrunk somewhat flattened, often with a slight depression between pronotum and mesonotum; gaster usually with clearly defined dark band across base of first segment. Antennal clubs pale brown to dark brown; anterior and dorsal faces of petiole meet at a distinct angle (Fig. 100) 23. unifasciatus (Latreille)

Dorsal outline of alitrunk convex without a break; gaster pale or dark but not banded; antennal clubs dark brown to black; dorsum of petiole rounded into anterior face without distinct angle (Fig. 99)................... 22. tuberum (Fabricius)

Queens

1 Antennae 11 segmented................................................................................ 2

Antennae 12 segmented............................................................................... 3

2(1) Scapes and tibiae with numerous suberect hairs.......... 17. acervorum (Fabricius)

Scapes and tibiae with sparse short adherent hairs....... 18. muscorum (Nylander)

3(1) Antennal clubs pale brown, concolorous with rest of funiculus......................... 4

Antennal clubs distinctly darker than rest of funiculus..................................... 5

4 (3) Propodeal spines robust; petiole high with distinct dorsal area; gaster usually banded; alitrunk yellowish............................................. 19. nylanderi (Forster)

Spines reduced to very short denticles; petiole low rising to an oblique angled peak without dorsal area; body colour including gaster evenly reddish brown 20. corticalis (Schenck)

5 (3) Mesoscutellum striate throughout; petiole with short truncate dorsal area; gaster not banded......................................................... 22. tuberum (Fabricius)

Mesoscutellum diffusely sculptured and shining; petiole angled or peaked in profile; gaster often distinctly banded............................................................. 6

6 (5) Propodeal spines reduced to short denticles, shorter than half the space between; alitrunk yellowish brown............................ 23. unifasciatus (Latreille)

Propodeal spines well developed, as long as space between; alitrunk brown to dark brown............................................................... 21. interruptus (Schenck)

Males

1 Antennae 12 segmented; scapes shorter than second funiculus segment............ 2

Antennae 13 segmented; scapes longer than second funiculus segment............. 3

2(1) Tibiae with numerous long suberect hairs; large robust species. Length 4-4.5 mm.......................................................................... 17. acervorum (Fabricius)

Tibiae bare or with very short hairs only; slender species. Length 3-3.5 mm (Fig. 95).................................................................... 18. muscorum (Nylander)

3(1) Space between notauli smooth; funiculus segments 2 to 5 twice as long as broad 4 Space between notauli sculptured; funiculus segments 2 to 5 less than twice as long as broad................................................................................................ 5

4 (3) Whole alitrunk smooth and shining............................... 20. corticalis (Schenck)

Sides of promesonotum finely striated............................ 19. nylanderi (Forster)

5 (3) Antennal segments 2 to 5 not longer than broad; propodeal spines very distinct; body uniformly dark and closely sculptured................ 21. interruptus (Schenck)

Antennal segments 2 to 5 slightly longer than broad; propodeal spines absent or reduced to faint tubercules; body colour pale to dark brown, general appearance more shining............................................................................... 6

6 (5) Area between notauli with rugulose sculpture throughout; petiole scarcely longer than high, ratio 10:8.2; scape as long as 4 following funiculus segments; appendages very pale brown (Fig. 101).......................... 22. tuberum (Fabricius)

Area between notauli with dilute sculpture, the striae almost obsolete in centre; petiole longer than high, ratio 10:7.2; scape as long as 3 following segments; appendages almost colourless................................... 23. unifasciatus (Latreille)