Lasius vestitus

Limited to the Pacific Northwest and northern California, this species is apparently exceptionally cold-tolerant as workers have been collected foraging on snow in Oregon's Cascade Mountains.

Identification
Closely related to Lasius umbratus but easily distinguished in both the queen and worker castes by its unusual body pilosity.

Distribution
Appears to be concentrated along the Pacific Coast, but extends eastward at least as far as western Idaho.

Distribution based on Regional Taxon Lists
Nearctic Region: Canada, United States.



Nomenclature

 *  vestitus. Lasius umbratus subsp. vestitus Wheeler, W.M. 1910e: 242 (q.) U.S.A. Wilson, 1955a: 174 (w.). Combination in L. (Chthonolasius): Emery, 1925b: 235. Raised to species: Creighton, 1950a: 425. Senior synonym of pilosus: Wilson, 1955a: 173.
 * pilosus. Lasius (Chthonolasius) pilosus Smith, M.R. 1934a: 384 (w.) U.S.A. Junior synonym of vestitus: Wilson, 1955a: 173.

Worker
(1) Exposed gastric tergites evenly covered with abundant, long, suberect-erect hairs; the longest over 0.12 mm., or exceeding four-fifths the maximum width of the hind tibia at its midlength. At least a few scattered standing hairs present on the scapes, femora, and tibiae.

(2) Size apparently about the same as in Lasius umbratus; PW range 0.66-0.73 mm. The worker is generally very similar to the large, hairy Eurasian form of umbratus, differing slightly in the length of the body pilosity as exemplified in the above description of the gastric pilosity. At the same time it is strikingly different from the sympatric North American form of umbratus and can be separated at once by its possession of standing hairs on the scapes and tibiae.

Queen
(1) Entire body, including the gula, genae, and outer lateral margins of the mandibles, densely covered with long, predominantly erect, silky-yellow hairs. Those on the gaster exceptionally uniform in length and inclination, lending the gaster a brush-like appearance in side view; the longest hairs on the tergites are 0.25 mm., approximately the maximum width of the hind tibia midpoint. These tend to be sparser and shorter on the sides of the alitrunk than on the dorsum, not exceeding 0.14 mm. The numerous hairs set along the dorsal petiolar crest and tibiae with abundant shorter, predominantly subdecumbent-erect hairs on all surfaces. Entire body covered with dense, appressed pubescence.

(2) Total size averaging smaller than other umbratus-complex members, and appendages averaging proportionately longer. HW and SI of all available specimens are as follows: 1.37 mm., 89; 1.42 mm., 90; 1.42 mm., 86; 1.42 mm., 87; 1.43 mm., 89; 1.43 mm., 90; 1.44 mm., 88; 1.46 mm., 85; 1.46 mm., 89; 1.52 mm., SI not measurable.

(3) Body color uniformly medium brown, the appendages light brown.

Type Material
HOLOTYPE. A queen in the, now in poor condition, with the head missing and much of the body pilosity broken down or worn off. Other queens in the same collection, however, show a detailed correspondence in all features that could be studied.