Lasius sitiens

Identification
A small, light-colored species with small eyes. Color typically medium yellowish brown, rarely dark yellowish brown. The scapes of the workers have hairs that are entirely decumbent, which separates this species from the somewhat similar co-occuring Lasius fallax. The latter has dense standing pubescence on its scapes. (Navajo Nature)

Distribution
Southwestern United States and northern Mexico.

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

Biology
Wilson (1955) - This species is limited to the lower altitudinal forest belts in the mountains of the Southwest, from juniper scrub at 7000 feet or less to mixed pine-spruce at 8000 feet. Judging from ecological notes accumulated by W. M. Wheeler, Cole, and myself, it nests almost exclusively under stones in dry, open situations. The type locality is situated in an area of open juniper scrub and scattered bunch-grass. Lasisus sitiens is co-dominant at this spot with several species of Myrmecocystus, Pogonomyrmex and Conomyrma. At the base of the San Francisco Peaks, near Flagstaff, I found sitiens again abundant, nesting under rocks in open pine forest. In New Mexico Cole has taken sitiens primarily in pine forest and clearings bounded by pine forest. The ecological extremes in which he collected this species are as follows: near Los Alamos, a nest in an open, grassy area with scattered pine and juniper at 6400 feet; near Taos, a nest in moist pine-spruce woods at 8000 feet.

The light coloration, small eyes, and shortened appendages of sitiens constitute a remarkable morphological convergence to the species of the subgenus Cautolasius, and specifically to the primitive species Lasius alienoflavus. There can be little question that the characters shared by these two species are the mark of a subterranean mode of life. At the type locality I was unable to find any workers foraging above ground either during the day or in the early night; in contrast, wherever the related species neoniger occurs its workers can nearly always be found above ground at any time of the day or night.

No nuptial flights of sitiens have been recorded. Reproductives have been taken in nido on six occasions, from July 2 (Campbell Blue Creek, Apache Nat. For., Ariz.) to July 30 (Bandelier Nat. Mon., N. Mex.). This would seem to indicate an early reproductive period similar to that of Lasius crypticus.

Nomenclature

 *  sitiens. Lasius (Lasius) sitiens Wilson, 1955a: 108 (w.q.m.) U.S.A.

Worker
(1) The outstanding diagnostic character is the small eye size: maximum eye length (EL) only 0.21-0.25 X the HW, whereas it always exceeds 0.25 X the HW in Lasius neoniger and Lasius crypticus and members of the niger complex. The maximum ommatidium number in a line along the long axis of the eye is typically 11 in sitiens, and occasionally 10 or 12; in related species it is typically 14 or 15 and occasionally 13 or 16.

(2) Averaging smaller than other members of the subgenus; PW rarely exceeding 0.56 mm. and usually less than 0.54 mm.

(3) Scapes and tibiae lacking standing hairs.

(4) Color typically medium yellowish brown, rarely dark yellowish brown.

PW maximum range 0.40-0.56 mm. In a sample of 53 from as many nest series, mean with standard error 0.472 ± 0.006 mm., standard deviation 0.042 mm. Appendages noticeably shorter than in related species. Scape index low, falling along the extrapolated Lasius brunneus SI-HW regression zone, but overlapping the lower extremity of the Lasius crypticus zone. The funiculus is also shortened, to the extent that flagellar segments I and II are as broad as long or slightly (never more than 1.3 X) broader than long, and segment III is as broad as long to slightly longer than broad; most of the range of this variation may be seen in single nest series. Maxillary palp segments V and VI subequal, quite short with respect to total body size, so that their length varies between 0.5 X and 0.8 X the maximum fore-tibia width. The head shape is slightly divergent from that of other species in that the largest workers show a ,'mature" allometric broadening of the head just behind the eyes; i.e. the allometric variation in head shape seen in larger species is expressed on a more diminutive scale in this species. Scapes and fore tibiae ordinarily devoid of hairs of any sort, although several decumbent to sub decumbent hairs were observed on the scapes in a single series from Sapello Canyon, New Mexico.

Queen
Very similar to the queen of crypticus, differing only in the following two characters.

(1) Averaging and ranging smaller; HW range in all available series 0.63-0.78 mm.

(2) Body medium to dark brown, with pale yellowish brown legs.

Male
In this caste the anterior border of the median lobe of the clypeus is broadly rounded, in contradistinction to the angular condition of the worker and queen of the same species, and males of neoniger and crypticus. Individuals are therefore not surely separable from small, faded alienus males. The following two characters represent distinctive trends but are not absolutely diagnostic.

(1) Averaging and ranging smaller than other members of the subgenus; HW range in all available series 0.63-0.78 mm.

(2) Body medium to dark brown, with pale yellowish brown legs.

Type Material
HOLOTYPE. A worker in the, selected from a nest series collected 20 miles north of Flagstaff, Arizona, on U. S. Route 89, July 25,1952, with associated winged queens and males (E. O. Wilson leg.). Paranidotypes in MCZ,, and Creighton Coll.