Lasius nearcticus

A predominately subterranean woodland species found in moist forests, it is most often seen when nest chambers are located under ground covering objects such as stones or logs. It is thought to feed on honeydew secreted by root-feeding aphids, however very little research has been done on this species, which lives and forages almost exclusively underground (Ellison et al., 2012).

Identification
This species is yellow or pale brown, and has small eyes (fewer than 35 ommatidia, usually about 20, diameter about 0.09 mm). The apex of the petiole is concave, the terminal segment of the maxillary palp is usually longer than the penultimate segment. (Mackay and Mackay 2002)

Ellison et al. (2012) - This is one of two New England species of Lasius with very tiny eyes; the other is Lasius flavus. These two species nest in distinct habitats – L. nearcticus in moist forests and L. flavus in open, dry habitats – but they can be distinguished reliably only by examining their maxillary palps at 25 – 50× magnification under a dissecting microscope. In L. nearcticus, the terminal segment of the palp is longer than the penultimate segment, whereas in L. flavus, the terminal segment of the palp is shorter than the penultimate segment.

Distribution
Common throughout most of the forested area from southeastern Canada to the southern Appalachian mountains. It is occasional as far west as South Dakota and Wyoming. (Wilson 1955). It is widespread in New England (Ellison et al., 2012).

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



Biology
Wilson (1955) - This species is most commonly encountered in dense, moist woodland. Workers and brood are usually found assembled in galleries under rocks and fallen logs, but by digging to the side away from these shelters, one can easily disclose lateral galleries leading off into the open soil, and workers are often turned up by random trenching through the soil.

A nuptial flight involving both sexes was observed by Dr. Mary Talbot (in litt.) at Gibraltar Island, Put-in Bay, Ohio, around 5 p.m. on August 26, 1930. I have verified the following in nido records of reproductives: Hull, Que., VIII-13-1913 (MCZ); Kingsmere, Que., IX-1-1913 (MCZ); Woods Hole, Mass., IX-23-1901 (MCZ); Arlington, Mass., VIII-30-1952 (E. O. Wilson leg.; MCZ), VII-17-1953 (W. L. Brown leg.; MCZ); E. S. George Reserve, Mich., VIII-23-1953 (M. Talbot leg. and Coll.) : Catawba, Ohio, VIII-18-1938 (M. Amstutz leg.; Talbot Coll.) ; South Bass Island, Ohio, VIII-15-1931 (Talbot leg. and Coll.); Green Island, Ohio, VIII-25-1932 (Talbot leg. and Coll); Louisville, Ky., IX-3-1950 (Wilson leg.; MCZ); Palo Alto Co., Iowa, VII-30-1946 (R. L. King leg. and Coll.); Dickinson Co., Iowa, VIII-17-1947 and VIII-17-1952 (King leg. and Coll.).

Nomenclature

 * mellea. Formica mellea Provancher, 1881b: 356 (w.) CANADA. [Unresolved junior primary homonym of Formica mellea Say, 1836: 286 (now in Camponotus).] [Also described as new by Provancher, 1883: 599.] Junior synonym of flavus: Dalla Torre, 1893: 185; Provancher, 1887: 236; of nearcticus: Francoeur & Béique, 1966: 144.
 *  nearcticus. Lasius flavus subsp. nearcticus Wheeler, W.M. 1906a: 38 (w.q.m.) U.S.A. Wheeler, G.C. & Wheeler, J. 1953c: 151 (l.); Crozier, 1970: 114 (k.). Combination in L. (Chthonolasius): Creighton, 1950a: 422; in L. (Cautolasius): Wilson, 1955a: 133. Raised to species: Wilson, 1955a: 133. Senior synonym of mellea: Francoeur & Béique, 1966: 144.

Worker
Wilson (1955) - (1) Segment VI of the maxillary palp distinctly longer than segment V.

(2) Scape long, always surpassing the occipital border by a considerable margin, the SI-HW regression zone well above those of the majority of series of other Cautolasius with the exception of the northern Eurasian population of Lasius flavus.

(3) Eyes small relative to head size, ommatidium number usually 9 to 17, but still averaging larger than in Lasius talpa.

(4) Differing from the sympatric eastern North American population of flavus by a number of other distinctive characters which break down in the allopatric western North American and Eurasian populations of flavus.

PW range 0.45-0.64 mm., maximum intranidal size variation 0.45-0.58 mm. (Gibraltar Island, Ohio; M. Amstutz leg.; Talbot Coll.). Apparently the least size-variable and most monomorphic of the four better known Cautolasius species. Mandibular dentition showing part of the variation seen in flavus: two well-developed teeth present and often a third, intercalary tooth in addition; the regular second intercalary tooth present in all specimens examined. Head covered with a dense ground pubescence, which obscures the margins of the head viewed in full face; this character also occurs in talpa and Lasius fallax but is only occasional in flavus. Color pale to medium yellow, the gaster often lighter than the alitrunk and the alitrunk lighter than the head; averaging and ranging overall lighter than other members of the subgenus.

Queen
Wilson (1955) - (1) Usually sharing the maxillary palp character of the worker. Single, exceptional, individuals from nest series from Catawba, Ohio (M. Amstutz leg., Talbot Coll. and MCZ) and McGregor Lake, Quebec (F. J. 0 'Rourke leg.; MCZ) have segment V equalling segment VI in length on one side only.

(2) Differing in size from the sympatric eastern North American population of flavus.

Male
Wilson (1955) - The diagnostic palpal character of the worker and queen is not shared by this caste; segment V is usually as long as VI and occasionally longer, the relative lengths showing considerable intranidal variability. The only possible distinctive character I have encountered is in the subgenital plate. In several Lasius neorcticus series examined it is shaped like a rectangle bent posteriorly, so that the anterior border is evenly convex and the posterior border evenly and deeply concave. The posteromedian setiferous area tends to be less prominent than in other Cautolasius and is one- or two-lobed. The subgenital plate of flavus is typically subquadrate in shape, although series from the Chilhowee Mountains of Tennessee are indistinguishable from nearcticus, while the plate figured by Clausen (1938) from Zurich is intermediate.

Mandible form showing the same extreme range of variation as in flavus, from the "palllitarsis type" to the "niger type."

Type Material
Wilson (1955) - The location of Wheeler's syntypes is unknown. The original description mentions workers from Illinois, Massachusetts, Connecticut, New York, and New Jersey, and it is possible that determined series in the from Colebrook, Conn. (Wheeler) and Woods Hole, Mass. (A. M. Field) were among the ones originally studied. For no stated reason Creighton (1950) selected Illinois as the type locality, even though no Illinois material is in the determined Wheeler collection. Since definitely authentic material may yet be discovered, it would be very unwise at this point to recognize any specimens as syntypes and to select a lectotype. Fortunately, Wheeler's description of the worker, his later determination of material in the MCZ, and his comments on the ecology ("only in damp soil in shady woods") leave little doubt that the present assignment of the name is correct.