Lasius occidentalis

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Lasius occidentalis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Formicinae
Tribe: Lasiini
Genus: Lasius
Species: L. occidentalis
Binomial name
Lasius occidentalis
Wheeler, W.M., 1909

Lasius occidentalis casent0172699 profile 1.jpg

Lasius occidentalis casent0172699 dorsal 1.jpg

Specimen labels

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

At a Glance • Temporary parasite  



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)

Keys including this Species


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 (type locality).
Neotropical Region: Mexico.

A dated view of Lasius occidentalis occurrence records (open circles) Wing 1968

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb


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.

This species belonged to what was long considered a separate genus (Acanthomyops). Wing (1968) published a revision of that taxon, summarizing some of their biology: These ants are exclusively subterranean in their habits, except for short periods of time just before and during nuptials. Nests are built in the soil, usually under the cover of objects such as stones or logs, but sometimes, especially in the Plains States, loosely compacted earthen mounds of varying size are made. Some taxa nest partially in rotted wood; these colonies are typically found in association with stumps and logs. Most taxa in the eastern states show a preference for fairly moist conditions, selecting fields, pastures, and woodlands as nesting sites. In the western states many taxa exhibit a greater tolerance for drier conditions in the selection of their nesting sites. Most myrmecologists believe that all species of Acanthomyops are temporary social parasites of Lasius. We have, however, very little evidence on the mode or modes of colony foundation in the genus - most of it being largely circumstantial. Work done by Tanquary (1911) represents the most determined effort to date to elucidate the nature of colony foundation in the genus. Methods of colony foundation in Acanthomyops are in critical need of solid evidence from field and laboratory studies. Many species of Acanthomyops are known to regularly attend subterranean aphids and coccids, which represent a wide variety of taxa. Probably the species whose biologies are unknown likewise subsist principally on the honeydew of these homopterous insects. At the time of the nuptial flights, which are more or less characteristic as to season for a given species, the workers in mature colonies of Acanthomyops open up the nest entrance widely by excavation. Nests in this condition are found readily even before the actual flights begin to occur. Flights occurring in natural surroundings often involve the participation of an extremely large number of alate individuals. The queens and males congregate on the ground, and, when the conditions are right, fly up into the air in large numbers. Later, many descend from their flight, often giving rise to large aggregations of ants in restricted local areas; this frequently leads to concern on the part of persons residing in the area. Nuptial flights sometimes originate from the basements of homes and stores. Confronted with the evidence of flights of the latter type, which usually take place during the winter months, occupants often fear that their buildings are infested with termites.


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)



The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • 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.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.



Wing 1968 Acanthomyops figs. 186-194

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.


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.


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 Museum of Comparative Zoology.


  • Bolton, B. 1995b. A new general catalogue of the ants of the world. Cambridge, Mass.: Harvard University Press, 504 pp. (page 53, catalogue)
  • Creighton, W. S. 1950a. The ants of North America. Bull. Mus. Comp. Zool. 104: 1-585 (page 432, Combination in Acanthomyops)
  • Mackay, W. P. and E. Mackay. 2002. The ants of New Mexico (Hymenoptera: Formicidae). Edwin Mellen Press, Lewiston, NY.
  • Ward, P.S. 2005. A synoptic review of the ants of California (Hymenoptera: Formicidae). Zootaxa 936: 1-68 (page 13, revived combination in Lasius (Acanthomyops))
  • Wheeler, W. M. 1909e. A decade of North American Formicidae. J. N. Y. Entomol. Soc. 17: 77-90 (page 83, worker, queen, male described)
  • Wing, M. W. 1968a. Taxonomic revision of the Nearctic genus Acanthomyops (Hymenoptera: Formicidae). Mem. Cornell Univ. Agric. Exp. Stn. 405: 1-173 (page 143, see also)