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Key to Lasius species in or possible in MS and AL (from Creighton 1950)
1 Maxillary palps with only 3 segments and very short
...2 (subgenus Acanthomyops)
  Maxillary palps with 6 segments and long
...6
2 Scapes surpassing occipital margin by an amount at least as great as the thickness of the tip of the scape
...3
  Scapes not surpassing occipital margin or if they do then by less than the thickness of the tip
...4
3(2)  The crest of the scale of the petiole covered with very numerous, close-set, short hairs with some of these hairs arising from the front of the scale giving the scale a brush-like appearance (possible)
 

Petiolar scale crest with only a few erect hairs arranged in a single row along the crest

4(2)     The fore femora usually without erect hairs, but if present then mainly confined to the flexor surface with only a few inconspicuous hairs  at the base of the lateral face (possible)
  Fore femora with erect hairs over much of the lateral face and on the flexor surface
...5
5(4)  In profile the petiolar scale with a blunt crest, from behind the crest is convex or flattened in the middle but not notched
  In profile the scale with a thin, sharp crest and seen from behind the crest is either deeply notched or at least with a median impression
6  The maxillary palps long with the last three segments subequal in length; the eyes large with about 200 facets present
...7 (subgenus Lasius)
  Maxillary palps short with the last three segments successively decreasing in length; eyes small with about 100 facets present at most, usually many less than that
...8
7(6)  The scapes with numerous erect or suberect hairs, these hairs obviously differentiated from the appressed hairs present; the promesonotal suture slightly but distinctly impressed; the promesonotal dorsum does not form a single even convexity
 

The scapes without erect or suberect hairs; the promesonotal suture not impressed or barely impressed; the promesonotal dorsum forms a single even convexity

8(6)     Eyes with only six or less facets in greatest diameter; queens are more than twice as long as workers
...9 (subgenus Cautolasius)
  Eyes with 10-12 facets in greatest diameter; queens less than twice as long as workers
..10 (subgenus Chthonolasius)
9(8)  Maxillary palp segment V as long as segment VI or longer; scapes reaching occipital margin but not surpassing it
  Segment VI of the maxillary palp distinctly longer than segment V; scapes surpassing occipital margin
10(8)  Scapes and tibiae with numerous erect hairs (possible)
  Scapes and tibiae with few or no erect hairs