Lasius occidentalis

This species nests under stones or logs in sandy soil or loam with scattered rocks.

Identification
The apex of the petiole of workers of this species is moderately sharp, and is usually notched. The hairs on the underside of the head are relatively short (less than 0.20 mm) and are present only on the posterior 1/2 to 3/4 of the surface. The erect hairs on the gaster are relatively short (less than 0.23 mm) and are scattered over the entire surface. (Mackay and Mackay 2002)

Distribution
British Columbia and Washington east to Manitoba and Minnesota with a southern extension to New Mexico.

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Mexico.



Biology
Data associated with specimens are scanty, and very little has been published on this species. The types came from several different nests, all under stones, in or near Colorado Springs, Colorado. The 4 collections I made in Anoka Co., Minesota all came from dry sandy soil. The 2 nests with alates taken in July had very low mounds, but it is by no means certain that mounds would be visible at other than flight time; these nests are discussed below. The other 2 nests were collected from under logs in the early spring. A Nebraska collection was made in sandy soil. A nest sample from Washington and one from Montana were both under stones. A nest sample from British Columbia was taken under a stone on a dry hillside. The altitudinal data available for a few of the 34 samples ranged from a little below 1000 to over 8000 ft. (Wing 1968)

Mackay and Mackay (2002), reporting on Lasius occidentalis in New Mexico: Occurs in meadows, pinyon-juniper, ponderosa pine forests, to spruce and aspen forests, including riparian meadows. Nuptial flights occurred at night during July and August (sexuals are attracted to black light traps). A dealate female was found loose in September.

Reproduction
Of 13 dated samples containing one or both sexes, only 1 did not include workers. These 12 samples are assumed to represent nest collections. A single queen was collected at light in Fort Collins, Colorado on July 26, 1935. The extreme dates for these collections are July 14 and August 17. The only available biological data on colonies with alates are from my field books. These notes cover 2 colonies collected in Anoka Co., Minnesota on July 21, 1950. The nests were in the middle of a sandy private road with sparse vegetation growing in its center. The workers had opened up the first nest by excavation; many were walking about on the surface of the ground near the nest openings. The collection was made in the early afternoon of a warm day with an overcast sky. Males and workers were collected by digging into the upper few inches of the nest. The second nest was located several yards down the road. All comments made on the first nest apply to this one, except that queens, males, and workers were taken from this nest. Both nests seemed ready to begin flights, awaiting the right combination of environmental conditions. From the meager data at hand it is not possible to delimit the flight period. However, it probably extends from mid-July to mid-August or later. (Wing 1968)

Nomenclature

 *  occidentalis. Lasius (Acanthomyops) occidentalis Wheeler, W.M. 1909e: 83 (w.q.m.) U.S.A. Combination in Acanthomyops: Creighton, 1950a: 432; in Lasius: Ward, 2005: 13. See also: Wing, 1968: 143.

Worker
Wing (1968) - Body size and eyes small; similar in appearance to some subglaber and most mexicanus specimens. Standing body hairs not delicate; posterior border of head as seen in full-face view feebly emarginate in some specimens. Pubescence moderate to dense and fairly short. Crest of petiolar scale sharp to moderate, usually emarginate. Crest of erect scale at or above level of propodeal spiracles. Sides of scale usually more or less straight and parallel. Propodeum in profile more or less straight, rarely convex. See treatment of subglaber for further diagnosis of these two closely related taxa.

Body and appendages pale yellow to brownish yellow, head often a little darker.

Queen
Wing (1968) - With rare exceptions this is the only taxon that has the posterior border of the head broadly and distinctly emarginated as seen in full-face view. Antennal scapes short, their tips reaching to a little beyond the posterior margins of the eyes. Scapes and funiculi only slightly clavate. Crest of petiolar scale sharp to moderately sharp; usually emarginate, often deeply so. Scale with sides straight, its width about equal to height from spiracle to crest. Body and appendages with pubescence moderately dense to dense. Scutellum with central area free of pubescence. CI 98 or less.

Color yellowish brown.

Male
Wing (1968) - Small, AL 1.05 - 1.30 mm, SL under 0.60 mm. Crest of petiolar scale sharp to moderately sharp, emarginate to straight, and with a row of flexed hairs. Width of scale about equal to its height above petiolar spiracles. Scutellum with pubescence absent centrally. Longer hairs at posterior tip of gaster less than 0.20 mm, often 0.15 mm or less.

Pubescence fairly dilute, body shining. Body and appendages brown, head piceous brown.

Type Material
Wing (1968) - Type locality: Colorado Springs, EI Paso Co., Colorado. Location of types: Syntypes in the.