Monomorium wilsoni, Espadaler, X., 2007

Espadaler, X., 2007, The ants of El Hierro (Canary Islands)., Advances in ant systematics (Hymenoptera: Formicidae): Homage to E. O. Wilson - 50 years of contributions., Memoirs of the American Entomological Institute, 80, pp. 113-127 : 118-119

8. Monomorium wilsoni , new species Figures. 4, 5, 6

Holotype queen: TL 4.7, HL 0.98, HW 1.05, CI 106, SL 0.82, SI 78, PW 0.66, ML 1.49.

Queen description (Figures 5, 6). Clypeus with the anterior margin feebly concave, without differentiated teeth. Clypeal carinae very weak. Frontal lobes with longitudinal superficial striae, present also between the base of mandibles and the eyes. Mandibles with four teeth. Head broader than long. Sides of head rounded. Antennae with 12 segments and the scape reaching the occiput. The posterior margin is concave, depressed in dorsal view. Eye maximum diameter 0.21 - 0.25, about 0.20 - 0.23 x HW, with 15 - 18 ommatidia in the longest row. Eyes with curved anteriorly pilosity of 0.04 - 0.05 mm. Mesosoma apterous. Sides of pronotum visible in dorsal view. Promesonotal dorsum in profile see fig. Scutellum saddle-shaped, rounded in profile. No traces of tegulae in the> 25 queens from 10 nests examined. Seen from above, petiole width 0.40 - 0.46, in profile with a posterior dorsal node two-faced. Postpetiole width 0.44 - 0.52, in profile with a vaulted node and a short ventral point. Whole body with a long pilosity. Whole body shining, with alutaceous microsculpture. Sides of propodeum and katepisternum with a fine reticulum. Declivitous face of propodeum transversely striate. General color brown. Mandibles, pronotum, anepisternum and metanotum reddish, contrasting with the brownish propodeum. Gaster blackish brown.

Worker description (Fig. 4). Clypeus as in the queen. Mandibles with 2 - 4 poorly developed longitudinal striae and four teeth, decreasing in size from apex to base. Palp formula 2, 2. Head longer than wide. Sides of head very slightly curved; vertex margin straight or very feebly concave. Scape surpassing the posterior border. Eye maximum diameter 0.12 - 0.14, about 0.23 - 0.27 x HW, with 9 - 11 ommatidia in the longest row. Promesonotal dorsum in profile with a well marked metanotal groove. Declivitous face of propodeum shallowly concave. Petiole higher than postpetiole. Anterior border of clypeus with a middle seta and 3 - 4 pairs of diminishing size towards the lateral margins. Median portion of clypeus with one pair directed anteriad and two pairs directed upwards. Dorsum of head with two pairs of standing hairs: one pair situated at the distal end of frontal lobes and one pair in midline of the head. Sometimes, a pair of shorter hairs is present between this last pair and the posterior margin. Posterior margin and dorsal mesosoma without standing hairs. Underside of head with 6 - 10 hairs of variable length. Petiole without hairs; postpetiole with 2 - 4 hairs directed posteriad. First gastral tergite with 0 - 2 hairs in front of the apical row. Dorsum of head shining, with piligerous pits and a very superficial alutaceous sculpture. Mesosoma shining. Sides and dorsum of propodeum, entire mesopleura and posterior half of propleura with visible reticulation that becomes increasingly superficial towards the anterior part of mesosoma. Body color brown with mandibles, antennomeres 3 - 12, lower half of petiole and postpetiole distinctly brownish red.

Additional paratype measurements, Workers: TL 2.4 - 2.7, HL 0.63 - 0.70, HW 0.50 - 0.57, CI 79 - 82, SL 0.57 - 0 - 62, SI 107 - 113, PW 0.32 - 0.36, ML 0.74 - 0.82. Queens: TL 4.7 - 5.1, HL 0.97 - 1.01, HW 1.01 - 1.06, CI 104 - 108, SL 0.82 - 0.84, SI 77 - 81, PW 0.64 - 0.68, ML 1.43 - 1.51.

Holotype queen: Spain, Canary Islands, El Hierro , Ermita de la Pena (N 27 º 48.091 ' W 17 º 58.779 '). 760 m. Rural, mountain pasture. 16.12.2003. (X. Espadaler), presently deposited in my personal collection ( XEPC). Paratypes. 16 workers, 8 queens, all same data as holotype. In eight pins, each pin with 2 workers, one female (queens), deposited in LACM, MCNC, MCZC and XEPC .

Additional specimens examined: 1, w; 3, w, q; 4, w, q; 8, w, q; 9, w; 10, w; 11, w, q; 12, w, q; 17, w; 18, w; 19, w, q; 21, w; 22, w; 28, w, q; 29, w, q; 32, w; 39, w, q; 41, w, q

Etymology. This species is named in honor of, and gratefulness to, Prof. Edward Osborne Wilson.

Remarks. The species is a member of the salomonis-group as defined by Bolton (1987). The closest relatives of this species belong to the whole group of endemic Monomorium from the Canary Islands, which have differentiated into a minimum of five species (unpublished observations). Specific differences are best appreciated in the apterous queen caste, in the density and length of pilosity, shape of mesosoma, petiole and postpetiole, and biometry. In the apterous queens of the species from the Canary Islands a cline can be established in which the more dense the pilosity, the shorter is, and the more advanced are queens in the stage towards an ergatoid condition. Variation in pilosity is best appreciated in head profile, petiole and postpetiole in dorsal view. The most modified species is M. hesperium Emery , in which queens are the smallest among the group in the Canary Islands and are next to completely smooth and shining and hairs are very long and comparatively sparse. M. medinae Forel , instead, is the most densely pilose but hairs are very short and head sculpture is more developed, as is also in the mesopleurae. M. wilsoni is intermediate in pilosity density and length. The head is wider than in M. medinae or M. hesperium . The mesosomal profile, especially the propodeum, the development of scutum and scutellum (side view) and the form of the strange petiole and postpetiole are also characteristic for each species. This peculiar modified thoracic structure is known in other Monomorium species and has been related to nest founding by budding (Bolton, 1986). Material is being collected for a revision of the entire group of endemic Macaronesian Monomorium .

Natural history. This is one of the most abundant ants at El Hierro. I collected it from sea level and up to 1300 m, under stones in open, dry, coastal habitats and up to the humid pine and laurel forests. This wide ecological plasticity is found also in its congener M. carbonarium in Madeira (unpub. observ.) and the Azores (Wetterer et al., 2004). Highly distinctive, the huge numbers of dark and shining workers attack and sting fiercely. No special skin reaction follows. The species is polygynous.