Lasius neoniger

Lasius neoniger's abundance coupled with its nesting in open habitats means it is one of the most commonly encountered ant species in the northeastern United States.

Identification
See the description section below.

Distribution
Lasius neoniger is abundant in eastern North America and as far west as North Dakota and Iowa. West of the Great Plains it apparently diminishes rapidly; it is rather uncommon in the southern Rockies and is thus far completely unknown from the Pacific Northwest.

This taxon was described from U.S.A.

Habitat
Open habitats.

Abundance
Common.

Biology
Wilson (1955) - This species nests almost exclusively in open areas, either under stones or in open soil in craters. In the eastern United States it is frequently the dominant ant in grassy road strips, lawns, cultivated fields, and other disturbed situations. By virtue of this ruderal adaptation it has become one of the most abundant and conspicuous insects within its range. The only natural habitats in which I have found it dominant are prairie (North Dakota, Montana) and old beach dunes (New England coast, Great Lakes). It never penetrates deep forests and is scarce in open woods and well shaded forest borders.

One of the most interesting features of its ecological distribution is its clearcut microgeographie replacement by the woodland species Lasius alienus. The two species overlap to a limited extent in open, sunny woodland, where both may be found nesting under stones. But the bulk of the neoniger population occurs in completely exposed situations, in craters and under stones, while most of the alienus are in rotting stumps and logs in well shaded woodland. This replacement pattern can be developed into an intricate mosaic where the habitats are suitable. Such a situation is found at Ipswich Beach, Massachusetts, for example, where the two species occur together in a small stretch of littoral woodland covering about fifty acres. The woods at this locality consist principally of small trees of Betula populifolia (grey birch), Prunus maritima (beach plum), Acer rubrum (red maple), Pinus rigida (pitch pine), and several species of oak. They are dense in low swampy areas where they provide leaf litter and humus of varying thickness to the loose, sandy soil. They are broken at intervals however, by foot paths, animal trails, and sand' 'blowouts". The latter are shallow, barren depressions in the sand in which only scattered grass and Hudsonia shrubs grow. neoniger is limited to these open areas, its craters often occurring in dense concentrations where the sand is firmly packed and moist several inches below the surface. L. alienus, on the other hand, is entirely limited to rotting stumps, logs, and branches on the shaded forest floor. Under natural conditions there is probably always an ample supply of such nesting sites, since Betula populifolia, the dominant tree, is very short-lived, and dead trees must always be in abundance. The two species are thus sharply segregated ecologically, with the neoniger population consisting of a series of enclaves within a more or less continuous woodland alienus population. No instances of overlap were found; the closest approach was a colony of alienus in a rotting log near the margin of a blowout and about seven feet from a cluster of neoniger craters.

Like other species of Lasius, neoniger is polyphagous, accepting both insect food and nectar. At Schroon Lake, N. Y. and Lake Constance, Ontario, I watched workers of this species foraging above ground in the early part of the night. The "trophophoric field" of the many nests observed did not seem to exceed two or three yards in radius, and the workers appeared to be engaged solely in gathering dead and crippled insects. A great variety of insects were accepted, including flies, leafhoppers, beetles, and spiders of various sizes. Using captive colonies maintained during a period of over a year, I have since learned that insects are readily accepted as food and are evidently necessary for successful colony growth.

The pastoral habits of this species have been dealt with in detail by S. A. Forbes' classic account (1894). He and later authors, including "W. M. Wheeler, have referred to the species studied as americanus (treated herein as a synonym of alienus), but there can be little doubt, judging from the descriptions of the ecology, nesting habits, etc., as well as from a drawing later published by Forbes, that it was really neoniger. The mutualistic relationship between the Lasius and the cornroot aphid (Aphis maidiradicus) as explored by Forbes is very similar to that later demonstrated by Eidmann (1926) between the European Lasius niger and an epigaeic species of aphid. The ants gather the eggs of the fall sexual brood of the aphid, store them in the nests over the winter, and in the spring excavate special galleries by means of which they are able to place the newly hatched nymphs directly on the corn roots. When strange aphids are freshly presented to the ants above ground they are promptly carried into the nest and placed on the roots also.

Talbot (1946) has studied diurnation in this species. In ordinary summer weather the workers are mainly nocturnal. Activity begins to rise in late afternoon, continues through the night, and declines through the following morning. The species prefers cool temperatures (50°-60° F.) and high humidity.

Forbes (1908) and Tanquary (1913) have studied the life history of this species in some detail. Nuptial flights are recorded by them for the period September 5-0ctober 18. Mr. B. D. Valentine (pers. commun.) has observed nuptial flights of this species on Long Island, New York, during the first week of September over a period of several years. It has been my observation that flights occur mainly in September in the Boston area also. The earliest record for a flight is one which I observed at Bishop, California, on July 30, 1952. In so far as I know the flights always take place during the second half of the afternoon; the one at Bishop continued to dusk. In the collections available to me, I have found winged forms associated in the nest with workers from July 25 (Salida, Colo.) to October 13 (Denver, Colo.). Forbes and Tanquary both showed that colony founding in this species resembles that later described for niger and Lasius flavus by Eidmann (1931). The fecundated queens overwinter without brood and start laying eggs in the following spring.

Nomenclature

 *  neoniger. Lasius niger var. neoniger Emery, 1893i: 639 (w.q.m.) U.S.A. (in text). Subspecies of niger: Wheeler, W.M. 1917a: 463; Buren, 1944a: 296; Creighton, 1950a: 420. Status as species: Gregg, E.V. 1945: 530; Wilson, 1955a: 97; Smith, D.R. 1979: 1436.

Description
Wilson (1955) - Worker and queen. Possessing the first two of the following characters in common with the other two members of the "neoniger complex" (Lasius crypticus and Lasius sitiens) and differing from these two species by the possession of the third.

(1) At least 20 per cent and often more than 90 per cent, of the nest series with the median of three basal teeth reduced in size relative to the two flanking teeth; in individuals where this tooth is absent, the space between the two remaining teeth is typically irregular in size and shape and usually larger in area than the basal-most tooth.

(2) The anterior border of the median clypeal lobe, when viewed in perfect full face (attaining maximum head length) and with the mandibles open, is obtusely angulate, the lateral faces straight and often meeting centrally to form a distinct angle; opposed to the broadly convex or parabolic condition of the "niger complex."

(3) Scapes and fore tibiae with abundant hairs, many of which are standing. The density declines allometrically, and nanitic workers (with PW about 0.40 mm.) may have seta counts of 0.

Worker
Wilson (1955) - PW 0.39 mm. (incipient colony) to 0.64 mm.; the range and dispersion are apparently about the same as for Lasius alienus (q. v.). SI of series of average-sized to large workers falling in the niger-alienu' regression zone, although two nanitics measured (Sudbury, Mass. incipient colony; Wilson leg.; MCZ) fell lower, just above the extrapolated brunneus zone — SL/HW ratios were 0.59/0.57 mm. and 0.59/0.58 mm. respectively. A similar dip in the regression zone has been observed in the sibling species Lasius crypticus, while the third member of the neoniger complex, Lasius sitiens, falls along the extrapolated Lasius brunneus zone. This indicates that the neoniger complex differs generally from the niger complex by having steeper regression zones. In body form, head shape, petiolar variation, etc., neoniger closely resembles niger and alienus. Appendage pilosity sparser and averaging shorter than in niger, with more hairs inclining to decumbent-subdecumbent, which condition occurs in niger in the Asiatic population only. Maximum color variation has been encountered within collections from the western U. S.: series from the White Sands National Monument, New Mexico, range to pale yellowish brown, with the head slightly darker than the remainder of the body; a series from Bishop, California, is a shade of dark brown about average for niger and alienus. The usual neoniger coloration is a light brown with feebly contrasting darker head.

Queen
Wilson (1955) - Size range and dispersion apparently about the same as for alienus. The dentition and clypeal characters of the worker are repeated in this caste with exaggerated effect. The clypeus is typically very angular, contrasting with the evenly convex condition of the niger complex and the flat-to-emarginate condition of Lasius pallitarsis. A peculiarity of the dentition in this caste is the frequent occurrence of an offset basal tooth similar to that characterizing pallitarsis; but when this occurs, it is often present on one mandible only, it is usually larger and more acute than in pallitarsis, and it is rarely if ever accompanied by secondary teeth on the basal border. The wings are more opaque than in the niger complex but lack the pattern of basal infuscation characterizing pallitarsis and brunneus.

Male
Wilson (1955) - Very similar to small individuals of niger except that the anterior border of the median clypeal lobe tends to be angulate as in the worker and queen. In the male this character is highly variable, however, and not all isolated individuals can be determined to species with certainty.

HW 0.74-0.86 mm., dispersion apparently about the same as for the North American populations of niger and alienus. Genitalia size and configuration, including the posterior lobing of the subgenital plate, apparently the same as for these two species.

Type Material
Wilson (1955) - LECTOTYPE. By present selection, a worker in the Emery Collection labelled "Va.".