Lasius pallitarsis

In North America, this ant abounds in boreal and cold-temperate habitats where it nests in rotten logs and stumps and under stones in forests. In northern Maine and eastern Canada, it is collected commonly in agricultural fields. Like Lasius americanus, L. pallitarsis is a generalist omnivore: it eats plant debris and other small insects, and tends aphids and other scale insects for their honeydew. It is the host of the temporary social parasites, and  (Ellison et al., 2012).

Identification
Ellison et al. (2012) - The large-eyed Lasius pallitarsis can be confused with any of the other three species in the niger group: Lasius neoniger, Lasius americanus or Lasius niger. The key distinguishing feature is that L. pallitarsis has a clearly defined offset, short, and upturned basal tooth on its mandible. This offset tooth is best seen in full-face view with the mandibles open, but if you can’t open the mandibles, count the teeth you can see. If you only see six (and the offset, seventh one is hidden under the clypeus), it is likely you have L. pallitarsis. (Ellison et al., 2012)

Distribution
This species ranges from eastern Québec across Canada to southeastern Alaska, south to Massachusetts in the east, and south through the mountains of California and the west. A single record exists from the southern Appalachian Mountains of North Carolina. (Ellison et al., 2012)

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

Biology
On Sable Island in Nova Scotia I have found Lasius pallitarsis associated with (Eriosomatini) Forda formicaria von Heyden, 1837. This introduced Palearctic aphid is an obligate myrmecophile which is found on the roots of grasses, and in this case was found on marram grass (Ammophila breviligulata). F. formicaria in Europe is most commonly associated with Lasius flavus but will also be found associated with Lasius niger if L. flavus is not present. (reported by Christopher Majka, 2020)

Wilson (1955) reported the following biological information under the synonymized name Lasius sitkaensis:

My own studies of sitkaensis in the field, combined with abundant field notes supplied me by A. C. Cole, Kenneth Kraft, G. C. Wheeler, and others, show that this species is primarily a forest dweller, nesting in rotting logs and stumps and under stones. It penetrates forest clearings secondarily and is abundant, at least locally, in the almost treeless plains of central and western North Dakota (P. B. Kannowski, Joe Davis, R. P. Uhlmann; material in G. C. Wheeler ColI. and UMMZ) and southern Idaho (A. C. Cole). In the latter situation it usually nests under stones but occasionally constructs irregular soil craters removed from any ground cover. At Moscow Mountain, Idaho, I found hundreds of nests in rotting wood and under stones within the forest margin, but only one associated with a crater in open soil. In Itasca State Park, Minn., Kraft found six colonies associated with craters, out of sixteen collected. Cole, in collecting Lasius from a wide diversity of habitats in New Mexico, took sitkaensis most consistently under stones in moist, shaded soil. At Cloudcroft, New Mexico, and the San Francisco Peaks, Arizona, I found the species most abundant well back in the shaded portions of the forest, nesting almost exclusively under stones. In the White Mountains of New Hampshire, however, sitkaensis populations are densest nesting under stones in overgrown meadows on the lower slopes, and are less abundant under stones in the adjacent spruce-fir-larch forest.

Local populations of sitkaensis and its relatives Lasius neoniger, Lasius americanus, and Lasius crypticus are often spectacularly dense. It seems inevitable that some amount of interspecific competition must result, and it is therefore not surprising to find a tendency for these species to replace one another ecologically where they occur together. Near Bemidji, in central Minnesota, I found sitkaensis in a deciduous woodlot nesting in rotting logs and stumps, a niche usually occupied by americanus in localities farther east where sitkaensis is rare or absent. neoniqer prevailed in adjacent open areas. At Kiowa, Montana, sitkaensis again seemed to replace americanus in deciduous woods; crypticus was abundant in an adjacent subalpine meadow, while neoniger, its nearest ecological equivalent, was absent. At Moscow Mountain and Cloudcroft, sitkaensis occurred in exceedingly large numbers, apparently to the exclusion of other members of the subgenus.

The food habits of sitkaensis are evidently generalized. Kannowski (in litt.) has found workers on several occasions associated with aphids in galleries under rocks, while at Moscow Mountain I observed workers carrying dead and crippled insects back to their nests during the early part of the night. A colony maintained under observation at the Harvard Biological Laboratories for nearly two years has readily accepted both honey and dead and crippled insects.

Winged forms have been taken in the nests from July 4 (Neche, Pembina Co., N. Dak.; E. L. Krause leg.; G. C. Wheeler Coll.) and July 7 (Cloudcroft, N. Mex., W. M. Wheeler leg.; MCZ) to September 24 (Lodema, Pembina Co., N. Dak.; Krause leg.; G. C. Wheeler Coll.). The great majority of in nido records are from August. G. C. 'Wheeler took pairs flying in copula at Marblehead, Mass., on September 3, 1927, and N. A. Weber took a pair in copula at Towner, McHenry Co., N. Dak., on August 18, 1927 (both G. C. Wheeler Coll.). Eidmann (1933) observed nuptial flights of "americanus" (probably the sitkaensis already referred to) in the Matamek region of Quebec on September 4. Borys Malkin found stray dealate queens at Wrangell, Alaska, in the first week of August.

In New Mexico (Mackay and Mackay 2002) - The most common species in the state. Occurs in grasslands to tundra, pinyon-juniper, especially common in ponderosa pine, ponderosa pine-riparian, pine aspen, fir forests, and Douglas fir, up to 2700 meters elevation. Nests are located under stones or under logs, under cow manure, in sandy or rocky loam soils. One colony was inside and under the bark of a rotten log, another in a stump and under the bark. Brood was present in nests from May to September, reproductives were found in nests from late July to late August. Flights occurred at night on 12-vii-1986 (black light trap) and between 8:00 and 9:00 and again between 18:00 and 19:00 on 6-viii-1982 at a single site (12 mi. NE Jémez Springs). This species is the host of Lasius subumbratus, of Solenopsis validiuscula and of the syrphid fly genus Microdon. One colony was nesting together with Crematogaster punctulata, one each with Formica lasioides, and ''[[Formica  argentea, another with Tapinoma sessile, two with Myrmica hamulata, and  three colonies were with Myrmica fracticornis. It is a host of the cricket, Myrmecophila sp. This is also a house infesting species. It is a very common ant in New Mexico, especially abundant near Bonito Lake in southern New Mexico.

Fungi
This taxon is a host for the fungi and (Espadaler & Santamaria, 2012).

Castes

 * Worker

Nomenclature

 *  pallitarsis. Formica pallitarsis Provancher, 1881b: 355 (w.m.) CANADA. [Also described as new by Provancher, 1883: 598.] Hung, 1969: 456 (k.). Combination in Lasius: André, 1887: 288. Junior synonym of alienus: André, 1887: 288; Wilson, 1955a: 77. Revived from synonymy and senior synonym of sitkaensis: Francoeur & Béique, 1966: 144. See also: Smith, D.R. 1979: 1437.
 * sitkaensis. Lasius niger subsp. sitkaensis Pergande, 1900: 519 (w.) U.S.A. Wheeler, W.M. 1917a: 525 (q.m.). Junior synonym of neoniger: Creighton, 1950a: 420. Revived from synonymy and raised to species: Wilson, 1955a: 36. Junior synonym of pallitarsis: Francoeur & Béique, 1966: 144.