Lasius umbratus

Identification
Clear yellow to reddish yellow; funiculus segments 2 to 4 slightly longer than wide. Scape elliptical in cross section. Petiole tapering to dorsal crest which is usually emarginate. Body surface and appendages covered in adpressed silvery pubescence. Longest hairs on gaster 0.06 mm to 0.11 mm, about half maximum hind tibial width. Erect hairs on genae, scapes and tibiae numerous. Length: 3.8-5.5 mm (Collingwood 1979).

Distribution
Widespread over both Eurasia and North America. In eastern North America Lasius umbratus occurs from Nova Scotia south to the Gulf States. Westward, umbratus is abundant through North Dakota, as evidenced by the large numbers of collections made in many localities in that state by G. C. Wheeler and his students. It appears to be relatively common in the southern Rockies, but sparse to absent over most of the rest of western North America.

This taxon was described from Finland.

Biology
Wilson (1955) - In the face of the revelation that umbratus has a common and hitherto poorly known Palaearctic sibling, Lasius rabaudi (=meridionalis Bondroit), the great mass of European literature pertaining to this species and its many synonyms cannot be accepted without major qualifications. It is in fact very probable that much of the literature deals with rabaudi instead of umbratus. Among the European authors, only Starcke (1937) seems to have fully realized the status and common occurrence of rabaudi and taken this taxonomic information into account in his ecological work. We are still very much in the dark as to whether the two species differ ecologically to any appreciable extent. In the following brief resume, reference to European literature on umbratus is made with the understanding that both species may be included.

In Europe, according to Gosswald (1932), Zimmermann (1934), Donisthorpe (1927), and others, umbratus is less common than the prominent members of Lasius s. s. It prefers dry areas and rarely nests in moist soil; Skwarra (1929) found it very rare on the wet Zehlau moors of East Prussia. It usually nests under rocks, but also occurs in rotting wood (including the timbers of houses), at the foot of trees, or in open ground. On occasion it builds mounds. Its preferred habitat is woodland, but it has also been taken along forest borders and in cultivated fields. In North America, where no sibling comparable to rabaudi is yet known, umbratus differs from the European population in that it prefers moist soil, but it still shows the same latitude in specific nesting sites. The majority of colonies have been taken under stones, while the rest have been taken in or about rotting logs and stumps. I do not know of any case of this ant building mounds or even nesting in the open soil in North America, as it (or rabaudi) has been known to do in Europe. In the northern U. S. east of the Mississippi River, umbratus is limited mostly to moist woodland, where it occurs under a wide variety of conditions of soil texture and insolation. In Alabama and Florida, at the southern extremity of the range, all of the several colonies recorded were found in rotting logs and stumps in swampland. In the western U.S., all of the collections with ecological data that I have examined were made under rocks in open forest and along or near forest borders. In New Mexico, A. C. Cole took this species between 7100 and 8000 feet, always under rocks but under variable conditions of soil moisture and vegetation, e.g. dry soil with scattered juniper and pine or oak and pine, moist soil in a clearing near a hardwood forest, and moist soil in an open grassy area.

As is the case in other species of Lasius, observations on the food habits of umbratus are entirely fragmentary and anecdotal. umbratus is generally thought to be subterranean and to subsist primarily on the excreta of aphids and coccids, since these insects are often found in great numbers in the galleries with the ants (cf. Donisthorpe, 1927, and Gregg, 1944). However, in Holland, Starcke (1937) has observed workers foraging aboveground at night and carrying insects to the nests presumably for use as food. Brown (pers. commun.) has also observed workers aboveground on cloudy days in Pennsylvania.

A number of nuptial flights recorded by Donisthorpe (1927), Crawley (1915), and Eidmann (1926) suggest a long flight season in Europe, extending from as early as August 8 (Crawley) to as late as October 7 (Eidmann). However, there is again no way of knowing whether these records might not represent the overlapping periods of the two species umbratus and rabaudi. Winged queens, determined by me as authentic umbratus, have been taken in Europe on the following dates: IV-4, V-11, VI-9, VI-12, VII-24, VII-31, VIII, VIII, VIII- (15-20), VIII-22, VIII-28, IX3, IX-10, IX-13, IX-16, IX-17, IX-29; these do not involve any apparent geographic trend and by themselves may indicate an unusually long flight period.

The situation in North America is somewhat similar. I have observed queens in flight in the environs of Boston, Mass., in September during two recent seasons. Lone dealate queens were found wandering above ground at Cambridge, Mass., on September 5, 1952, and October 2, 1953, and at Plantagenet, Ontario, on June 30, 1952. Dates on which winged forms have been taken alone or in nido cover the same period, as shown by the following randqm sample: VI-28, VII-8, VII-27, VIII-I, VIII-8, VIII-13, VIII-13, VIII-18, VIII-20, VIII-31, IX-I, IX-5, IX-9, IX-27, X-14, X-28, X-29. Since there are no known sibling species to complicate the picture in North America, the data here suggest that on this continent at least umbratus has an unusually long nuptial season.

There is no evidence to indicate that the reproductives of umbratus build aerial swarms during their nuptial flights, as do those of Lasius niger and Lasius flavus, although this does not preclude the possibility. Eidmann (1926) observed queens of umbratus (or rabaudi?) flying singly in Germany, and I have observed definitely determined umbratus queens flying singly on two occasions in the Boston area.

Donisthorpe (1927), Crawley (in Donisthorpe, ibid.), Gosswald (1938), and Holldobler (1953) have reported in detail on the colony founding behavior of "umbratus" and "Lasius mixtus". The normal hosts are niger and Lasius alienus. Under both field and laboratory conditions dealate umbratus queens attack host workers as they encounter them away from the nests, seizing them up the mandibles and carrying them about as they resume foraging. Their victims are usually killed by this treatment and may eventually be eaten. With the fulfillment of this Mordinstinkt, as Holldobler calls it, and the presumed acquisition of the host odor, the queens are ready and able to enter host colonies, although they may be subjected to further attack before acquiring final acceptance. Unfortunately, the authors who have witnessed this phenomenon failed to make a convincing distinction between umbratus and rabaudi, and specimens were not saved to allow corroborative determinations during the present revision.

During the falls of 1952 and 1953 I collected numerous dealate umbratus queens at Cambridge, Mass., and tried introducing them into colonies and colony fragments of Lasius pallitarsis, alienus, and neoniger, but never obtained a complete adoption and saw no evidence of the Mordinstinkt behavior. I have also worked on the theory that the umbratus may join recently fecundated host queens, since both host and parasite queens are often found in species-pure groups under rocks following nuptial flights. Various attempts to bring umbratus and neoniqer queens together, including placing them in the same chamber while chilled, have so far failed; the reason may be, however, that neoniger is not a natural host. I would like to suggest, on what admittedly constitutes negative evidence, that behavior in the population I studied may differ from that in the European populations. If true, this could be due either to geographic variation or to the fact that the European authors were using rabaudi instead of umbratus. Only additional research accompanied by careful determinations will settle the matter.

niger and alienus probably serve as hosts of umbratus in North America as they do in Europe. I have seen two mixed niger-umbratus nest series from Ute Park, New Mexico (A. C. Cole leg. and Coll., MCZ) and one alienus-umbratus series from Beatty, Pennsylvania (Schmitt leg.; MCZ). The Beatty umbratus are minimas. Buren (1944) found a single dealate “aphidicola" queen with a depauperate colony of "flavus nearcticus”, but to my knowledge there has been no additional evidence forthcoming that this or any other Chthonolasius uses species of Cautolasius as hosts.

Collingwood (1979) reporting on umbratus in Europe - This species nests under boulders, in tree stumps and at the base of old trees. Workers are subterranean and seldom or never seen above ground. Flight period from mid August to late September. Single queens found colonies by invasion of and adoption in Lasius niger, Lasius alienus or occasionally Lasius brunneus nests. In late summer dealate queens often wander over the surface of L. niger nests, sometimes carrying a dead L. niger worker as a prelude to securing adoption.

Nomenclature

 *  umbratus. Formica umbrata Nylander, 1846b: 1048 (q.m.) FINLAND. Schenck, 1852: 59 (w.); Hauschteck, 1962: 219 (k.); Hung, 1969: 456 (k.). Combination in Lasius: Mayr, 1861: 50; in Donisthorpea: Donisthorpe, 1915d: 223; in Formicina: Emery, 1916b: 241; in Acanthomyops: Ruzsky, 1925b: 44; in Chthonolasius: Ruzsky, 1936: 91; in Lasius (Chthonolasius): Ruzsky, 1914a: 59; Müller, 1923: 129; Emery, 1925b: 233; Wilson, 1955a: 150. Senior synonym of belgarum: Wilson, 1955a: 150; Seifert, 1988a: 150; of hirtiscapus: Wilson, 1955a: 150; Seifert, 1990: 11; of affinoumbratus, aphidicola, epinotalis, exacutus, nyaradi, osakana, silvestrii and material of the unavailable names mixtoaffinis, mixtobicornis referred here: Wilson, 1955a: 150; of mixtoumbratus: Wilson, 1955a: 150; Kutter, 1977c: 14. See also: Stitz, 1939: 291; Bernard, 1967: 363; Kutter, 1977c: 232; Yamauchi, 1979: 168; Seifert, 1988a: 150; Atanassov & Dlussky, 1992: 245; Radchenko, 2007: 34.
 * aphidicola. Formica aphidicola Walsh, 1863: 310 (w.q.m.) U.S.A. Wheeler, G.C. & Wheeler, J. 1953c: 150 (l.). Combination in Lasius: Mayr, 1886d: 429; in L. (Chthonolasius): Ruzsky, 1914a: 61. Junior synonym of flavus: Mayr, 1886d: 429. Revived from synonymy: Dalla Torre, 1893: 182. Subspecies of umbratus: Wheeler, W.M. 1908g: 406; Buren, 1944a: 297. Junior synonym of umbratus: Wilson, 1955a: 150.
 * exacutus. Lasius umbratus var. exacutus Ruzsky, 1902d: 15 (w.) RUSSIA. Combination in Acanthomyops: Ruzsky, 1925b: 44; in Lasius (Chthonolasius): Ruzsky, 1914a: 61; Emery, 1925b: 234. Subspecies of umbratus: Ruzsky, 1905b: 287. Raised to species: Ruzsky, 1925b: 44. Subspecies of bicornis: Menozzi, 1939a: 314 (in key). Junior synonym of umbratus: Wilson, 1955a: 150.
 * affinoumbratus. Lasius umbratus var. affinoumbratus Donisthorpe, 1914: 40 (w.) GREAT BRITAIN. Junior synonym of umbratus: Wilson, 1955a: 151.
 * belgarum. Formicina belgarum Bondroit, 1918: 31, fig. 17 (w.q.) BELGIUM. Combination in Lasius (Chthonolasius): Emery, 1925b: 234. Subspecies of umbratus: Stärcke, 1937: 57; of mixtus: Stitz, 1939: 299. Junior synonym of umbratus: Wilson, 1955a: 151; Seifert, 1988: 150.
 * silvestrii. Lasius (Chthonolasius) silvestrii Wheeler, W.M. 1928d: 120 (q.) JAPAN. Junior synonym of umbratus: Wilson, 1955a: 152.
 * hirtiscapus. Lasius umbratus var. hirtiscapus Stärcke, 1937: 43 (q.) CZECHOSLOVAKIA. Subspecies of mixtus: Stitz, 1939: 299. Junior synonym of umbratus: Wilson, 1955a: 152.
 * osakana. Lasius (Chthonolasius) silvestrii var. osakana Santschi, 1941: 278 (q.) JAPAN. Junior synonym of umbratus: Wilson, 1955a: 152.
 * nyaradi. Chthonolasius affinis var. nyaradi Röszler, 1943: 47 (w.q.) ROMANIA. Junior synonym of umbratus: Wilson, 1955a: 152.
 * epinotalis. Lasius (Chthonolasius) umbratus subsp. epinotalis Buren, 1944a: 297 (w.) U.S.A. Junior synonym of umbratus: Wilson, 1955a: 152.

Worker
Wilson (1955) - (1) Pilosity and pubescence as in queen. Maximum length of hairs of first gastric tergite anterior to the extreme posterior strip 0.06-0.08 mm., not exceeding one-half the maximum width of the hind tibia at midlength. Alitruncal and cephalic hairs with maximum length of about 0.11 mm.

(2) Petiole in frontal view tapering slightly from the widest point, just above the foramina, to the dorsal crest. The dorsal crest broad and very variable in outline, from flat or even feebly convex to deeply concave; the emargination rounded or angular, never as deep as in Lasius bicornis, i.e. the width (taken at the midpoint of the depth measurement) always exceeds the depth. Intranidal variation considerable; the petiole in a single series may range from flat to distinctly emarginate. In side view the scale is relatively narrow, its dorsal crest acute.

Queen
Wilson (1955) - (1) Most of the body surface covered with abundant, relatively short, silvery yellow, predominantly erect hairs. The hairs on the first three gastric tergites with maximum length variable internidally, 0.05-0.11 mm., never more than one-half the maximum width of the hind tibiae at midlength, and often less than one-third; very variable in density, never less than 20 hairs visible above the dorsal profile of the first gastric segment seen in perfect side view and usually more than 30, but never dense enough to overlap one another extensively, Erect hairs forming a fringe on the dorsal crest of the petiole, their maximum length close to that of the gastric hairs. The longest hairs of the alitrunk are on the scutellum, maximum length 0.12-0.21 mm. Maximum length of scutal hairs 0.05-0.15 mm. (see also under geographic variation). Maximum length of cephalic hairs exclusive of those on the clypeus 0.09.-0.11 mm. Body hairs mostly straight or feebly curved, rarely strongly curved (on propodeum) and never sinuate. Standing hairs mayor may not be present on the appendages (see also under geographic variation). All of body and appendages densely covered with short, whitish pubescence which is completely appressed on the body and appressed to decumbent on the appendages; on the gaster it is often abundant enough to obscure partly the shining cuticular surface and to present a whitish overcast to the naked eye.

(2) HW ranging 1.40-1.82 mm. in 45 nest series measured (see also under geographic variation). SI of size extremes 75 and 81.

(3) Petiole in frontal view tapering gradually but distinctly from the level of maximum width (just above the foramina) to the dorsal crest, the width just ventral to the dorsolateral angles 0.9 X the maximum width or less but the frontal outline rarely subquadrate as in rabaudi. Dorsal crest extremely variable in shape, from very feebly concave or even straight to deeply concave with the emargination almost right-angular. The dorsolateral angles always broadly rounded. In side view the scale is narrow and with an acute dorsal crest.

(4) The scape short-elliptical to circular in cross-section, never conspicuously flattened, the minimum width at the midpoint 0.11 mm. or greater. The third funicular segment 1.0-1.5 X longer than broad.

(5) Body medium to dark brown, the appendages lighter, light to medium brown.

Male
Wilson (1955) - (1) Pilosity and pubescence essentially the same as in the queen and worker, except that hairs of the first three gastric tergites are more frequently subdecumbent-suberect. Despite this greater tendency toward obliqueness, the hairs of the first gastric tergite are still too sparse to show much overlap, and their maximum length (excluding those on the extreme posterior strips) ranges internidally 0.07-0.08 mm., or always less than 0.7 X the maximum width of the hind tibia at its midlength. Maximum length of scutellar and cephalic hairs (excluding those on the clypeus) 0.09 mm.

(2) HW 0.85-1.23 mm. in 15 nest series measured; SI of the extremes 62 and 66.

(3) Petiole in frontal view tapering dorsally as in queen and worker. Dorsal margin flat to deeply emarginate, the emargination rounded or angular, never greater than semicircular or rightangular. The scale in side view relatively thin, with an acute dorsal crest.

Type Material
Wilson (1955) - LECTOTYPE. A dealate queen in the Helsinki Museum, selection by Starcke (1937).

Additional References

 * Collingwood, C. A. 1979. The Formicidae (Hymenoptera) of Fennoscandia and Denmark. Fauna Entomol. Scand. 8:1-174.