Lasius humilis

This ant is typically found by locating nesting chambers under objects on the ground (e.g., rocks or logs). It occurs in a variety of habitats, at high elevations (~2,000 m +).

Identification
This small, pale yellow Lasius has very small eyes. The promesonotal suture is absent and the dorsal crest of the petiole when viewed from the front is wedge-shaped, tapering to form an angular, non-emarginate median prominence.

Key to Lasius workers, queens

Distribution
Western United States.

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



Biology
Beyond collection record details reported in a number of publications not much is known about the biology of this species.

Wilson (1955): "Dr. Cole has kindly supplied me with the following notes on his Colorado and New Mexico collections. The Trinidad, Colo., colony was found under a stone in the moist soil of a mountain meadow. The Tesuque Canyon, N. Mex., colony was found under a stone in moist, open pine-aspen woods."

Allred (1982): "Forty five ants in two collections were found under logs, one in grass, herbs, aspen, and pine, and one in pine" (Utah records).

Gregg (1963): "This ant is extremely rare, and though the majority of the records to date are from Colorado, they by no means indicate that the center of its geographic range lies within this state. We now know that the ant is distributed over a wide area in the Rocky Mountains and Great Basin Region, but from the little that has been learned of its ecology, it seems likely the range is a discontinuous one in widely isolated localities which happen to provide the required environmental conditions.

In addition to the record we possess from canyon meadow in Castle Park, Dr. Cole's specimens from south of Trinidad were living under a stone in moist mountain-meadow soil. Cole's New Mexico record came from Tesuque Canyon, Hyde State Park, near Santa Fe, at an elevation of 8700 ft., and was again under a stone but in moist pine-aspen woods. The conditions under which Wheeler's Salida specimens were obtained seems not to be known.

The Colorado stations all are in the Upper Sonoran Zone, as far as I can tell, although Cole's Trinidad record would appear to be just on the border of the Transition, but until an unequivocal site for this ant in the submontane of Colorado is established I prefer to leave its zonal distribution as stated above. Although our actual altitudinal records for humilis in Colorado do not state elevations as high as 7000 feet, Wheeler's specimens from Salida must of necessity be from this altitude at the minimum."

Mackay and Mackay (2002) - Occurs in sagebrush, pinyon-juniper, mountain meadows, pine aspen woods, ponderosa pine forests. This species nests under stones. Reproductives were found in nests in early July, flights occur at night in mid July (blacklight traps), and a loose gynes were collected in pitfall traps from early July to mid August.

Nomenclature

 *  humilis. Lasius (Formicina) humilis Wheeler, W.M. 1917a: 528 (w.q.) U.S.A. Combination in L. (Chthonolasius): Emery, 1925b: 233. See also: Wilson, 1955a: 185.

Worker
Wilson (1955) - This caste by itself may at first be confused with nanitic workers of Lasius umbratus, but differs in the obliteration of the promesonotal impression and in the unusual petiole shape.

(1) Very small; extreme PW range of all series examined 0.53-0.63 mm.

(2) Promesonotal impression seen in side view very feeble or lacking.

(3) Eyes small relative to head; EL range 0.12-0.15 mm.

(4) Dorsal crest of the petiole in frontal view wedge-shaped, tapering upward to form an angular, non-emarginate median prominence.

(5) Body color uniformly light yellow.

Queen
Wilson (1955) - (1) The smallest North American Chthonolasius known; HW of the three syntype queens measured 1.04, 1.06, and 1.06 mm, respectively.

(2) Scapes longer relative to head width than in any other small Chthonolasius; SI of syntypes 85, 88 and 90 respectively, whereas in Lasius umbratus, Lasius rabaudi, Lasius minutus, and Lasius bicornis SI probably never exceeds 82 or 83 and is usually less than 80.

(3) Standing hairs absent from the appendages and sparse on the body. Seen in full face, no more than one or two standing hairs project beyond the entire cephalic contour posterior to the mandibular insertions. Gastric pilosity short and fine; gastric pubescence abundant and completely appressed.

(4) Body and appendages medium yellow, the occiput and thoracic dorsum lightly infuscate.

Type Material
Wilson (1955) - LECTOTYPE. By present selection, a queen in the Museum of Comparative Zoology labelled "Pyramid Lake, Nev. W. M. Mann." HW 1.04 mm, Additional syntype queens and workers are in the Museum of Comparative Zoology. A queen and two workers in the T. W. Cook Collection are probably also part of the original type series, despite their differing label "Pyramid Lake, Nev. 4-6-45."