Lasius subumbratus

Identification
A close relative of Lasius umbratus sympatric with that species over most of its range and best distinguished from it by differences in body pilosity.

Distribution
This taxon was described from U.S.A.

Nomenclature

 *  subumbratus. Lasius umbratus subsp. subumbratus Viereck, 1903: 73 (q.) U.S.A. Wheeler, W.M. 1910e: 238 (w.m.). Combination in L. (Chthonolasius): Emery, 1925b: 235. Raised to species: Creighton, 1950a: 424. See also: Wheeler, W.M. 1917h: 167; Wilson, 1955a: 175.

Worker
Wilson (1955) - (1) Gastric pilosity longer and denser than in Lasius umbratus. The hairs-on the first tergite with a maximum length of about 0.10 mm., or about 0.6 X the maximum width of the hind tibia at its midlength, mostly decumbent-subdecumbent (occasionally tending to suberect), and dense enough for the individual hairs to overlap one another widely. Scapes, femora, and tibiae with dense, predominantly decumbent pubescence and occasional standing hairs (umbratus in all populations with sparser pubescence, often appressed, and the North American population always lacking standing hairs). Gaster with very sparse pubescence, not obscuring in any way the shining cuticular surface.

(2) Eyes smaller than in North American umbratus, the HW-EW regression zones of the two species well separated, although no single absolute measurement will suffice to separate all the series. The Eurasian population of umbratus connects and overlaps the two. (3) Size averaging larger than in umbratus, PW range 0.55-0.85 mm.

(4) Body and appendages uniformly medium yellow, lighter than most North American umbratus and Lasius minutus.

Queen
Wilson (1955) - (1) Pilosity on anterior three gastric tergites very long (maximum length 0.24-0.27 mm., or approximately the maximum width of the hind tibia at midlength), silvery yellow, and predominantly decumbent-subdecumbent. Similar erect hairs form a fringe around the entire dorsal and lateral margins of the petiole; these are often curved toward their tips. Pilosity of alitrunk mostly limited to the dorsal surface, from the posterior margin of the pronotum to the dorsal face of the propodeum, averaging shorter than on the gaster and petiole, maximum length about 0.24 mm., subdecumbent to erect, often curved or sinuate. Pilosity of head mostly limited to the occipital zone, averaging shorter than on the alitrunk, maximum length about 0.18 mm., predominantly subdecumbent-suberect and often curved.

(2) Averaging larger and with proportionately longer appendages than the sympatric North American population of umbratus. Extreme range of HW with attendant SI of series examined 1.56 mm., 85; 1.74 mm., 83.

(3) Color averaging lighter than in umbratus. Body typically medium yellowish brown, head somewhat lighter; appendages light yellowish brown.

Male
(1) Gastric pilosity similar to that of worker in form and inclination, but sparser, more often subdecumbent, and showing only limited overlap between individual hairs; maximum length of hairs about 0.13 mm., or 0.9-1.1 X the maximum width of the hind tibia at midlength. Maximum length of the hairs of the posterior two-thirds of the clypeus 0.12 mm., or slightly less than 0.10 X the HW.

(2) Averaging larger than in umbratus; maximum range in all series studied 1.05-1.17 mm.

(3) Genitalia similar in all respects to those of umbratus.