Lasius balearicus

Lasius balearicus displays a peculiar geographical distribution, as it has been solely reported from the top summits of the island of Mallorca. All localities where the species has been collected lay between 800 and 1400 metres above sea level. A typical habitat composition included rocky calcareous surfaces, with sparse and shrubby vegetation, and frequently composed of the endemic plants Hypericum balearicum and Genista valdes-bermejoi. Specimens were collected from nests under stones and on nearby vegetation, frequently tending aphids.

Identification
Seifert (2020) - A species related to Lasius cinereus and Lasius grandis. Absolute size small (CS 850 µm; according to Talavera et al. (2014) ranging from 0.69–0.93 mm). Head and scape length indices large (CL/CW900 1.094, SL/CS900 1.011); postocular distance and torulo-clypeal distance higher than in Iberian sister species (PoOc/CL900 0.234, dClAn900 5.43); eye size rather small (EYE/CS900 0.236); terminal segment of maxillary palp rather short (MP6/CS900 0.186). Number of mandibular dents large (MaDe900 8.60). Pubescence on clypeus more dilute than in sister species (sqPDCL900 5.00); frontal pubescence very short (PLF900 23.0). All body parts with very numerous standing setae of medium length, number of genal setae in particular much larger than in Iberian sister species (PnHL/CS900 0.135, GuHL/CS900 0.133, nGen900 14.5, nGu900 17.8, nSc900 22.6, nHT900 20.1). As difference to L. cinereus, the surface within the meshes of the microreticulum on lateral pronotum is perfectly smooth and shining. In contrast, and resembling the situation in L. cinereus, fine punctures (ultrastructures) within these meshes are present on dorsum of pronotum – as result the surface appears completely matt. Meshes of microreticulum on dorsum of head without or with only occasionally these ultrastructures. Coloration: the entire body is yellowish brown, with head and gaster slightly darker and antennae and tarsae slightly paler.

The identification of Lasius balearicus should be clear by a combination of small size, very high setae numbers on basically all body parts, the shape characters reported above and the peculiar distribution.

Talavera, Espadaler & Vila (2014) - The species belongs in the subgenus Lasius s. str. as conceived by Wilson (1955). The maxillary palp segments V and VI are subequal in length to segment IV and eye length is at least 0.20 9 the head width. Those two characters in combination define Lasius s. str. The small size, high pilosity, and a distinct coloration are the three main diagnostic characteristics typifying Lasius balearicus.

Using the dichotomous key in Seifert (1992) this species would key to couplet 28 although its morphology does not fit either of the two species under the dichotomy Lasius platythorax and Lasius grandis. Specifically, by the character HL/HW (900) it would correspond to L. grandis and by the character SL/HL (900) it would be L. platythorax. Coloration of L. balearicus is also clearly distinct from that of those two species. Seifert’s (1992) key could be amended as follows in order to include L. balearicus:

28

 * HL/HW (900) < 1.070 . . . . Lasius platythorax''


 * HL/HW (900) > 1.070 . . . . . 28a

28a

 * SL/HL (900) > 0.982. Size much bigger (HL 1037 ± 0.06) and less hairy (nHS 22.8 ± 7.3) . . . . . Lasius grandis


 * SL/HL (900) < 0.982. Size smaller (HL 0.88 ± 0.05) and hairier (nHS 35.8 ± 5.3) . . . . . Lasius balearicus

The combination of morphology and colour of L. balearicus is unique. Small body size, AND coloration AND marked hairiness characterize L. balearicus. Specifically, the number of standing hairs on dorsal profile of the scape is the highest among known species of Palaearctic Lasius. The number of tibial hairs is also very high, only surpassed by the Asiatic Lasius hirsutus, from which it differs by the much denser gaster tergite pubescence in L. balearicus. Colour is also diagnostic. Taken in isolation, workers of L. balearicus are reminiscent of recently eclosed Lasius grandis or Lasius cinereus, which are the morphologically and phylogenetically closest species. All examined workers have the same, consistent, coloration. When dry, the gaster is somewhat darker that the head and alitrunk.

Within the Palaearctic Lasius s. str. species, the closest species are L. grandis Forel and L. cinereus Seifert, both species having a Western Mediterranean distribution (Seifert, 1992; Espadaler et al., 2011). Lasius grandis, as its name indicates, has a bigger size, with HL (standard deviation) 1.03 (0.06), a less hairy scape and legs, with nHS 22.8 (7.3) and nHHT 25.6 (6.7), and denser clypeal pubescence (PDCL 19.3 (4.9). Lasius cinereus, with its entirely dull mesosoma, is clearly separable from L. balearicus, whose pronotum sides are shining. Hairiness is less developed in L. cinereus, especially in the scape, with nHS 22.2 (3.5), and nHHT 21.7 (2.4). Clypeal pubescence is denser (20.5 (5.1)) in L. cinereus. The molecular phylogeny shows that L. balearicus is sister to both L. grandis and L. cinereus, from which it apparently diverged approximately 1.5 Ma.

Distribution
Seifert (2020) - Island endemic. Only known from the top summits of the island of Mallorca at elevations between 800 and 1400 m.

Distribution based on Regional Taxon Lists
Palaearctic Region: Spain.

Nomenclature

 *  balearicus. Lasius balearicus Talavera, Espadaler & Vila, 2014: 9, figs. 1, 4 (w.) SPAIN.

Worker
[n = 51 for all variables but PDCL (n = 20) and mandibular dents (n = 48)]. Mean; SD (range). Head longer than wide; HL 0.88; 0.05 (0.73–0.97), HW 0.80; 0.05 (0.65–0.89), HL/ HW 1.09; 0.02 (1.04–1.12). HL/HW (900) 1.101. In frontal view the head profile is entirely hairy, up to the mandible base ; nBH 22.92; 3.28 (13–30). Clypeal pubescence rather diluted, similar in density to L. platythorax; PDCL 26.43; 4.87 (19–42). Clypeal carina variable, even in individuals of the same nest: from being clearly expressed in the anterior two-thirds to totally absent. Scape usually shorter than head length; SL 0.85; 0.05 (0.67–0.93), SL/HL 0.96; 0.02 (0.91–1.03). SL/HL (900) 0.966. Very hairy scape; nHS 35.82; 5.38 (26–52). Very hairy tibiae; nHHT 29.78; 4.61 (17–40). Mandibular dents 8.55; 0.57 (8–10). Surface characters: frontal head with very visible punctures. Microreticulum is more developed at the posterior third of the head surface, and most developed in the disk of pronotum. Space between punctures and microreticulum is shining. Colour: the entire body is yellowish brown, with antennae and tarsi clearer.

Type Material
Holotype: worker collected in Coll des Prat, Escorca, Mallorca, Spain, 39°48’29.86″ N 2°51’4.52″ E, 1194 m, 13.x.2008, code 08R384, R. Vila & G. Talavera leg. Deposited at the Natural History Museum (London, UK).

Paratypes. 14 workers from the same nest as the holotype. Coll des Prat, Escorca, Mallorca, Spain, 39°48’29.86″ N 2°51;4.52″ E, 1194 m, 13.x.2008, code 08R384, R. Vila & G. Talavera leg. 15 workers, Puig des Teix, Mallorca, Spain, 39°43’56.74″ N, 2°38’53.03″ E, 919 m, 12.x.2008, code 08I725, R. Vila & G. Talavera leg. 15 workers, pic Tomir, Mallorca, Spain, 39°50’13.88″ N, 2°55’19.46″ E, 1048 m, 14.x.2008, code 08R372, R. Vila & G. Talavera leg. Two workers, Coma de n’Arbona, Mallorca, Spain, 39°48’5″N, 2°47’8.99″E, 1200 m, 2009, code PM053, A. Traveset leg. One worker, Puig des Teix, Mallorca, Spain, x.1982, C.A. Collingwood leg. One worker, ses Clotades, Mallorca, Spain, 39°48’33.99″N, 2°47’49.99″ E, 1330 m, 15.vi.2011, code PM1006, C. Tur leg.

Three paratype workers from the same nest as the holotype deposited at each of the following institutions: Museum of Comparative Zoology (Cambridge, MA, USA), Natural History Museum (London, UK) and Senckenberg Museum (G€orlitz, Germany). Three paratype workers from Puig des Teix deposited at the Museu Balear de Ciencies Naturals (S_oller, Mallorca). Other paratype material in the authors’ collections [Institut de Biologia Evolutiva (CSIC-UPF) and Universitat Aut_onoma de Barcelona, both in Barcelona, Spain].

Etymology
The specific name is derived from the Balearic Islands.

References based on Global Ant Biodiversity Informatics

 * Talavera G., X. Espadaler, and R. Vila. Discovered just before extinction? The first endemic ant from the Balearic Islands (Lasius balearicus sp. nov.) is endangered by climate change. Journal of Biogeography doi:10.1111/jbi.12438