Lasius fallax

Identification
A population inhabiting the Rocky Mountains and Great Basin from Idaho and Montana south to southern Arizona, almost exactly intermediate in each of the critical diagnostic characters separating Lasius flavus, Lasius nearcticus and Lasius talpa. (Wilson 1955)

Distribution
Washington, Idaho, Montana, Wyoming, Colorado, Utah, Arizona.

This taxon was described from U.S.A.

Nomenclature

 *  fallax. Lasius (Cautolasius) fallax Wilson, 1955a: 130 (w.q.m.) U.S.A.

Worker
1) Outer surfaces of the tibiae with numerous standing hairs prominent above a dense ground pubescence. Scapes with dense standing pubescence grading into hairs of intermediate length ( ¼ - ½ X as long as the maximum scape width) but with few or no outstanding hairs along the plane of count.

(2) Relative lengths of the two terminal segments of the maxillary palp very variable within individual nest series, grading from the flavus condition (segment V equal to or longer than segment VI) to the nearcticus condition (segment V shorter than segment VI). The flavus condition usually preponderates, and the nearcticus condition may be altogether absent in any single nest series.

(3) The allometric regression zones for both ommatidium number and scape length relative to head width appear to be exactly consistent with those for the western North American population of Lasius flavus, which is intermediate between Lasius nearcticus and the sympatric eastern population of flavus. The minimum recorded ommatidium number is 12, higher than in the majority of Lasius talpa series.

PW range 0.44-0.70 mm., maximum intranidal range 0.44-0.56 mm. (Hartzel, Colo.) and 0.49-0.67 mm. (Kaibab Nat. For., Ariz.). Head shape usually more like that of nearcticus than flavus, i.e. sub quadrate with widely spaced mandibles; intermediate in the Monticello, Utah series. Cephalic pubescence as in nearcticus. Mandibular dentition similar to nearcticus, showing part of the flavus variation; two basal teeth always present, occasionally with a third, intercalary tooth, and a second intercalary tooth present in all specimens examined. Color of body and appendages medium yellow to very light yellowish brown, head often a shade darker than the rest of the body.

Queen
Appendage pilosity as in worker. Terminal maxillary palp segments as in flavus, varying within single nest series from segments V and VI equal in length, to V longer than VI. Size variation similar to that of nearcticus and western North American- Eurasian flavus; HW 1.38-1.55 mm. Color similar to flavus, darker than talpa.

Male
At least 2 or 3 and usually more than 6 standing hairs along the outer lateral femoral surfaces; in nearcticus rarely more than 1 or 2 and usually none. Mandible form varying as in other Cautolasius.

Subgenital plate of male from Lost River Range, Idaho, subquadrate, with a single prominent median setiferous lobe. Lacking the extended posterolateral flanges of talpa.