Lasius

Lasius is one of the most prominent and familiar of the Holarctic ant genera. From the time of Reaumur in the eighteenth century (Wheeler, 1926), European and North American entomologists have focused attention on it in countless general biological and taxonomic investigations which are today part of the classical foundation of myrmecology. It is probably best known for its conspicuous nuptial flights, its habit of tending and transporting homopterous insects, and the temporary parasitic behavior of some of its species. It has also attracted much attention as one of the several ant genera which have persisted in Europe and North America since early Tertiary times with only a small amount of visible evolutionary change. (Wilson 1955)

Identification
The morphological distinctions between Lasuis and Acanthomyops have always been unambiguous but it has taken a recent molecular phylogenetic analysis (Janda et al. 2004) to settle whether or not these two groups represent two distinctive genera. The latter is well accepted today as a synonym of Lasius. It remains convenient for identification purposes to distinguish Acanthomyops as a distinctive species group within Lasius.

Nearctic species of Lasius with long maxillary palpi, those that were once thought to be distinctive from Acanthomyops, can be determined to species using this key by Wilson (1955) :
 * Key to Nearctic Lasius workers with long maxillary palpi

Wing (1968) provides the following in his revision of the Neartic Acanthomyops: Acanthomyops has short, 3-segmented maxillary palpi, while those of Lasius are 6-segmented and long. Another attribute of Acanthomyops that serves as a convenient diagnostic character for field collectors using a mouth-type aspirator is the presence of a characteristic odor produced by the mandibular glands of disturbed workers. This odor, a defense mechanism, is like that of oil of citronella or lemon verbena. As sensed by a collector with normal olfactory powers the odor is pronounced. A few species of Lasius possess a similar odor, but it is sensed, at most, as quite weak. Lasius umbratus probably has the strongest odor of any species of Lasius, yet it is decidedly weaker than that of all species of Acanthomyops I have collected.


 * Key to Nearctic workers of Acanthomyops - the short key
 * Key to Nearctic Acanthomyops workers
 * Key to Nearctic Acanthomyops queens
 * Key to Nearctic Acanthomyops males

There is also a somewhat outdated (1955) and restricted (no Nearctic Acanthomyops queens and males):
 * Key to Lasius queens and males

Distribution
Lasius occupies a purely Holarctic range. Northward it reaches northern Scandinavia, the Baikal region of Siberia, Kamchatka, southeastern Alaska, and southern Labrador. Southward it reaches Madeira, North Africa, northern Iraq, the southern Himalayas, the mountains of Formosa, the mountains of central Mexico, and northern Florida. Where it comes closest geographically to tropical faunas, as in southeastern Asia, it still retains its north-temperate character, i.e., limited to temperate vegetation at higher elevations and there associated chiefly with typically Holarctie ant genera. (Wilson 1955)

Biology
Within this range it is among the most abundant of all insect genera. In Europe the two species Lasius niger and Lasius flavus are often the overriding dominants of the ant fauna in local situations and under a variety of ecological conditions. In the eastern United States neoniger mounts such dense populations in open fields and lawns that W. M. Wheeler was once moved (1905) to suggest that it might be the most abundant insect in North America. Such a contention would probably be an exaggeration with respect to all insects, of course, yet there is no denying neoniger its importance as a major faunal influent within its range and favored habitat.

Lasius is also remarkable - perhaps unique - among animal groups thus far monographed, in its great abundance, ubiquity, and conspicuousness, and the consequent ease with which it can be found in the field. Anywhere in the northern United States, in practically all but desert and semidesert conditions, it is possible for an investigator to walk onto nearly any plot of ground and within a matter of minutes find nests of one or more species. (Wilson 1955)

Species Uncertain
Unknown species of Lasius are hosts for the nematodes (Wahab, 1962),  (Wahab, 1962),  (Crawley & Baylis, 1921),  (Wahab, 1962), and the eucharitid wasp  (Universal Chalcidoidea Database) (primary host).

Nomenclature

 *  LASIUS [Formicinae: Lasiini]
 * Lasius Fabricius, 1804: 415. Type-species: Formica nigra, by subsequent designation of Bingham, 1903: 338.
 * [Lasius Jurine, 1801: 164 (Apidae), resurrected by Morice & Durrant, 1915: 421, suppressed by Act of Commission.]
 * Lasius junior synonym of Acanthomyops: Forel, 1916: 460; Donisthorpe, 1916c: 276; Morice & Durrant, 1917: 442. Donisthorpe, 1927b: 206; Donisthorpe, 1937b: 132; Donisthorpe, 1943f: 655; Donisthorpe, 1946g: 91.
 * Lasius junior synonym of Formicina: Emery, 1916a: 61; Bondroit, 1918: 19.
 * Lasius as genus: Wheeler, W.M. 1916k: 172; Emery, 1925b: 226; Wilson, 1955a: 11.
 * Lasius senior synonym of Donisthorpea: Wheeler, W.M. 1916k: 172; Emery, 1925b: 226; Wilson, 1955a: 11.
 * Lasius senior synonym of †Tylolasius: Hong, Wu & Ren, 2001: 348.
 * Subgenera of Lasius: nominal plus  Acanthomyops, Austrolasius, Cautolasius, Chthonolasius, Dendrolasius. 
 * DONISTHORPEA [junior synonym of Lasius]
 * Donisthorpea Morice & Durrant, 1915: 423. Type-species: Formica nigra, by original designation. [Unnecessary replacement name for Lasius Fabricius.]
 * Donisthorpea as genus: Donisthorpe, 1915d: 184.
 * Donisthorpea subgenus of Formicina: Emery, 1916a: 11; Emery, 1916b: 239.
 * Donisthorpea subgenus of Acanthomyops: Donisthorpe, 1927b: 229; Donisthorpe, 1946g: 91.
 * Donisthorpea junior synonym of Acanthomyops: Forel, 1916: 460; Morice & Durrant, 1917: 442; Donisthorpe, 1927b: 209.
 * Donisthorpea junior synonym of Lasius: Wheeler, W.M. 1916k: 172; Wilson, 1955a: 11.
 * [Lasius and Donisthorpea share the same type-species, synonymy is therefore absolute.]
 * †TYLOLASIUS [junior synonym of Lasius]
 * †Tylolasius Zhang, J. 1989: 295. Type-species: †Tylolasius inflatus, by original designation.
 * †Tylolasius junior synonym of Lasius: Hong, Wu & Ren, 2001: 348.