Lasius casevitzi

This species is endemic to Corsica where it is a common species. It does not occur in xerothermous grassland unlike other members of the L. paralienus complex and prefers semi-arboreal habitats and dry open forest. Nests are in soil, under trees or under stones. It is absent from the coastal environment and from elevations above 1100 m. The altitudinal extremes within 50 records were 23 m and 1100 m, with the majority of nests found between 300 m and 800 m. Alates were not observed in the nests during collecting in July and August. The ants behave aggressively during disturbance of the nest by the collector.

Identification
Seifert and Galkowski (2016) - The species of the Lasius paralienus complex are separable from related species by the combination of low clypeal pubescence distance, low setae numbers on scape and differences in length of maxillary palp segments. Lasius alienus, Lasius psammophilus and Lasius piliferus are the most similar species occurring within the geographic range of the three L. paralienus complex species. L. alienus differs from the other five species by having strongly reduced setae numbers on the metapleuron below the level of the propodeal spiracle. A safe separation of individual workers is possible by a discriminant function considering head width, the length of the terminal maxillary palp segment and clypeal pubescence distance.

Distribution
L. casevitzi is clearly a Corsican endemic. Due to its comparably strong isolation, this Mediterranean island has many endemic insect species with rather strongly deviating characters. Among ants these are Temnothorax melas, Temnothorax corsicus, Formica corsica and Plagiolepis delaugerrei.

Distribution based on Regional Taxon Lists
Palaearctic Region: France.

Nomenclature

 *  casevitzi. Lasius casevitzi Seifert & Galkowski, 2016: 54, figs. 6-9 (w.) FRANCE (CORSICA).

Worker
Numeric data given in the following description are primary data (without removal of allometric variance) of 18 measured individuals.

Rather small-sized, CS 849 ± 41 [779,912] μm. Basic morphology not different from other members of the Lasius alienus group. Head moderately elongated, with convex sides and straight posterior margin of vertex, CL/ CW 1.078 ± 0.019 [1.039,1.123]. Scape rather long, SL/CS 1.006 ± 0.016 [0.981,1.036]. Eye medium-sized and moderately distant from posterior margin of head, EYE/CS 0.242 ± 0.004 [0.236,0.248], PoOc/CL 0.247 ± 0.005 [0.239,0.254]. Antennal socket situated rather close to posterior clypeal margin, dCLAn/CS 4.43 ± 0.26 [4.06,4.97]%. Masticatory border of mandibles with 8-9 teeth. Maxillary palps with six segments and much longer than in related species, MP6/CS 0.214 ± 0.009 [0.201,0.235]. Pubescence on whole body surfaces dense and whitish, sqPDCL 3.35 ±0.20 [3.00,3.72]. Mean length of pubescence hairs between frontal carinae 36.9 ± 2.23 [32.9,40.5] μm. Pilosity compared to next related species rather rich and long—in particular on genae and tibiae. Eyes with several microsetae of 11-16 μm length. Scape with no or very few standing setae: nSc 1.20 ± 0.89 [0.0,3.0]. Genae and extensor profile of hind tibia with more erect setae than in the next related species: nGen 3.86 ± 0.71 [2.5,5.0], nHT 7.85 ± 1.73 [5.5,12.5]. Underside of head and hind margin of vertex with rather numerous standing setae: nGu 3.69 ± 0.94 [2.0,6.0], nOcc 11.90 ± 1.83 [9.5,15.5]. Metapleuron below level of propodeal stigma with rather many erect to suberect setae: nSt 4.72 ± 0.87 [3.0,6.0]. Length of setae on pronotum rather large: PnHL/CS 0.157 ± 0.018 [0.107,0.175]. Whole body concolorous medium to dark brown; mandibles, scape and sometimes tibia lighter reddish or yellowish brown. Mesosoma in lateral view with an angulate-convex propodeal dome. Petiole scale low, in frontal view with slightly convex sides converging towards the dorsal crest which is straight or slightly convex.

Type Material

 * Three paratype workers with same site labeling as the holotype, stored in Muséum National d’Histoire Naturelle Paris.
 * Three paratype workers from the holotype nest and four paratype workers from another nest at the holotype locality labeled "FRA: 42.440°N, 8.868°E, 687 m Corse: Bonifatu, leg. Galkowski 2015.07.12 -2" in Senckenberg Museum für Naturkunde Görlitz.
 * Three paratype workers from the holotype nest and four paratype workers from another nest at the holotype locality labeled "FRA: 42.440°N, 8.868°E, 687 m Corse: Bonifatu, leg. Galkowski 2015.07.12 -2" in Senckenberg Museum für Naturkunde Görlitz.

Etymology
The species is dedicated to Janine Casevitz-Weulersse who investigated the Corsican ant fauna over many years.