Lasius xerophilus

Occurs in arid and semi-arid Chihuahuan Desert northwards into Utah. Nests are found in the soil, usually in sandy sites. The nest entrance is small, inconspicuous, and surrounded by a small mound. Foraging activity is nocturnal or crepuscular, except on cloudy, cool days, when it continues throughout the day. Nests contain about 100 workers. Flights occur at night in July. (Mackay and Mackay 2002)

Identification
This species is similar to Lasius neoniger, and would key to this species in Wilson (1955). It differs in that the worker is covered with short, bristly hairs. The extensor surface of the front tibia has at least 6, usually over 10 such hairs (usually 1 or none in L. neoniger), the same surface of the mid tibia has up to 14 such hairs (usually fewer than 10 in L. neoniger) and the same surface of the posterior tibia has more than 15 (fewer than 15 in L. neoniger).

The queens are also much more hairy, with more than 20 hairs on the extensor surface of the mid tibia and hind tibia (fewer than 6 on these surfaces in L. neoniger).

The extensor surface of the mid tibia of the male has more than 5 erect hairs (1 or none in L. neoniger), the hind tibia has more than 10 erect hairs (0 - 2 in L. neoniger). (Mackay and Mackay 2002)

Further Identification Details
Mackay & Mackay (1994) - This new species is a member of the neoniger species complex, which also includes L. neoniger, Lasius crypticus and Lasius sitiens (Wilson 1955). The distributions of several related species (L. niger, L. neoniger, Lasius alienus, L. sitiens, and L. crypticus) are near to or overlap the distribution of this species. Thus a comparison with these species is necessary to reduce the possibility of misidentifications. The workers, females and males can be distinguished by the abundant erect hairs from most others, except Lasius pallitarsis, from which the workers and females differ by not having the offset basal mandibular tooth. The workers of L. niger are also hairy, but can be distinguished as they are darker brown than the light yellowish brown L. xerophilus workers. In addition, the penultimate and terminal basal teeth are subequal in size in L. niger. The new species can be distinguished from L. neoniger by the abundant hair on the tibiae, especially the fore tibia. The workers of L. alienus, L. crypticus and L. sitiens usually lack erect hairs on the scapes and tibiae, which easily separates these species from the new species. Lasius crypticus also inhabits dry, exposed situations and thrives in short-grass prairie semidesert transition (Wilson, 1955).

The males are similar to others in the niger species complex, differing primarily in the abundant erect hairs on the mid and hind tibiae. Males of L. alienus, L. crypticus and L. sitiens have few or no erect hairs on the scapes, which easily separates them from those of L. xerophilus.

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



Biology
Mackay & Mackay (1994) - All specimens of this species from White Sands National Monument were collected in the extensive sand dunes (gypsum). Small inconspicuous nests were found in interdune areas. Foraging was nocturnal and crepuscular, except on cool days, when activity continued throughout the day. Nests apparently contained about 100 workers. They appeared in habitus in the field to be a species of Dorymyrmex, although they are much slower and not very excitable. Workers were timid and attempted to hide when nests were excavated. Sexuals were found in nests in July. Flights occurred at 20:00-23:00 on July 24, 1992 at the Visitor’s Center.

Nomenclature

 *  xerophilus. Lasius xerophilus Mackay, W.P. & Mackay, E.E., 1994: 37, figs. 1-7, 9 (w.q.m.) U.S.A.

Type Material


Paratype material, 54 paratype workers, 4 paratype females and 35 paratype males, have been deposited in the Harvard Museum of Comparative Zoology, Los Angeles County Museum of Natural History, the American Museum of Natural History, the New Mexico Museum of Natural History, the British Museum of Natural History and in the Laboratory for Environmental Biology, University of Texas.

Taxonomic Notes
This species was recorded from White Sands National Monument and was considered by Wilson (1955) to be Lasius neoniger, although it differed in being "exceptionally hairy and lighter in color" than typical L. neoniger workers. Wilson concluded that both of these characters may represent adaptations to the extreme environment at the site. (Mackay & Mackay, 1994)

Description
Worker measurements (mm): HL (head length) 0.84-0.86, HW (maximum head width) 0.80-0.83, SL (scape length) 0.75-0.79, EL (eye length) 0.20-0.21, WL (Weber’s length) 0.93-0.98, CI (cephalic index, HW/HL 100) 95-97, SI (scape index SL/HL 100) 87-94.
 * Worker

Mandibles with 5 large, well defined acute teeth, widely spaced with two denticles (intercalaries) between preapical (second), median (third) and first basal (fourth), apical tooth about twice size of preapical tooth, which is equal in size to remainder; anterior border of clypeus broadly rounded, surface of clypeus convex, bulging; frontal area poorly defined; sides of head broadly convex, eyes reaching lateral margins, located about 1 1/2 diameters from base of mandible; vertex slightly concave; scapes extending past occipital borders by about 2 funicular segments; maxillary palps long, extending nearly to foramen magnum; pronotum broadly rounded; surface joining mesonotum at same level, promesonotal suture well marked (lateral view); propodeum rectangular shaped, somewhat narrowed dorsally, well differentiated from mesonotum, dorsal face short (0.12 mm), posterior face long (0.4 mm); petiolar node concave apically. Erect, coarse, bristly hairs (0.05-0.1 mm long) abundant on all surfaces, golden, decumbent pubescence abundant on head, dorsum of mesosoma and gaster. Light brown, gaster darker brown. Mandibles finely striate, dorsum of head and most of mesosoma and gaster finely punctate. Posterior face of propodeum smooth and shining.

Female measurements: HL 1.46-1.48, HW 1.64-1.65, SL 1.19-1.23, EL 0.38-0.40, WL 3.18-3.26, CI 111-113, SI 81-83.
 * Queen

Mandible similar to that of worker, except teeth between second, third and fourth teeth larger, about half size of others; eyes large, about 1.5 diameters from base of mandibles; 3 well developed ocelli; vertex straight; scape extends past occipital corner by length of first funicular segment; petiolar node strongly bilobed. Sculpture, hair and pubescence as in worker. Head and dorsum of mesosoma dark brown, side of mesosoma and gaster lighter brown.

Male measurements: HL 0.65-0.69, HW (posterior to eye) 0.68-0.74, SL 0.49-0.51, EL 0.29-0.30, WL 1.43-1.51, CI 99-113, SI 71-78.
 * Male

Mandible without teeth except single angle at apex, rarely a second poorly defined tooth may be present (seen in one specimen); masticatory border broadly convex; median anterior border of clypeus broadly convex, surface convex; head wider posteriorly than anteriorly; eyes large, convex, about 1/2 diameter from base of mandible; 3 ocelli well developed; scape about as long as first 5 funicular segments; maxillary palps short, reaching about 1/3 distance to foramen magnum; petiolar node broadly concave; parameres thickened, apex covered with erect hairs; aedeagus with well developed convex blade, without teeth; volsella broad with digitus poorly developed. Erect, bristly hairs on all surfaces, but not as abundant as in worker and female. Punctate throughout, except for smooth surface of posterior face of propodeum. Dark brown, scapes, legs and genitalia lighter brown.