Veromessor julianus (Pergande, 1894)

Johnson, Robert A., Borowiec, Marek L., Snelling, Roy R. & Cole, Arthur C., 2022, A taxonomic revision and a review of the biology of the North American seed-harvester ant genus Veromessor (Hymenoptera: Formicidae: Myrmicinae), Zootaxa 5206 (1), pp. 1-115 : 40-52

Veromessor julianus

( Figures 1D , 20–25 )

Distribution— Figure 27A

Aphaenogaster juliana Pergande, 1894: 164 (worker). Syntypes examined: 1 worker [ CASC], 5 workers [ USNM], #4479 , MEXICO, Lower California (= Baja California Sur): San Julio, no date (Dr. Gustav Eisen). See also Creighton and Wheeler, 1934: 368, plate II, fig. 7. CASC worker here designated LECTOTYPE [CASTYPE00619].

Stenamma (Messor) julianum (Pergande) ; Emery, 1895: 308 (first combination in Stenamma [ Messor ]).

Aphaenogaster (Messor) juliana Pergande ; Forel, 1899: 59 (first combination in Aphaenogaster [ Messor ]).

Novomessor (Veromessor) julianus (Pergande) ; Forel, 1917: 235 (first combination in Novomessor [ Veromessor ]).

Veromessor julianus (Pergande) ; Wheeler and Creighton, 1934: 368 (first combination in Veromessor ).

Messor julianus (Pergande) ; Bolton, 1982: 341 (first combination in Messor ).

Veromessor julianus (Pergande) ; Ward, Brady, Fisher, and Schultz, 2015: 13 (revived combination in Veromessor ).

Veromessor julianus subsp. clarior Wheeler and Creighton, 1934: 370 (worker). Syntypes examined: 3 workers [LACM], 6 workers [ USNM], MEXICO, Baja California Sur: San José de Comondú , February 1923 (H.C. Millender). NEW SYNONOMY. USNM worker here designated LECTOTYPE [USNMENT00529096].

Veromessor julianus subsp. manni Wheeler and Creighton, 1934: 371 . Syntypes examined: 2 workers [USNM], MEXICO, Baja California Sur: Las Parras (see below), no date (Dr. W.M. Mann). NEW SYNONOMY. USNM worker here designated LECTOTYPE [CASENT0922841].

Worker diagnosis. This species is uniquely characterized by the following combination of features: (1) head and gaster light to dark brownish-orange to dark brown; mesosoma lighter orangish-brown or head, mesosoma, petiole, postpetiole dark ferruginous orange; gaster dark brown to blackish, (2) medial lobe of clypeus with 2–3 moderately coarse longitudinal rugae on either side of medial groove, medial lobe not thick and protuberant in profile, not elevated above lateral lobes in frontal view, (3) mandibles with 8 teeth, (4) dorsal base of scape weakly flattened, weakly widened; maximum basal width of scape distinctly less than maximum preapical width, (5) MOD usually much less than OMD, OI <25.0, (6) cephalic dorsum with fine, closely spaced, wavy, longitudinal rugae; medial rugae diverging toward posterior corners; cephalic interrugae weakly to moderately punctulate, moderately shining, (7) psammophore well developed; ventral surface of head capsule with many long J-shaped hairs arranged in a distinct row around the outer margin of the ventral region of the head capsule, (8) dorsum of pronotum with mostly transverse, weakly to strongly irregular rugae, rugae often with lateral branches and/or becoming rugoreticulate posterad; sides of pronotum variable: with irregular vertical and/or longitudinal rugae or rugae mostly confined to anterior one-half, posterior one-half strongly granulate or strongly granulate over entire surface, interrugae and granulate surfaces dull; mesonotum with irregular longitudinal rugae, rugae sometimes with short lateral branches, interrugae weakly coriarious, moderately shining to strongly granulate, dull or entire surface strongly granulate, dull; mesopleura variable: strongly granulate between irregular, longitudinal and/or oblique rugae, rugae often with short lateral branches on dorsal one-half, irregular longitudinal rugae on ventral one-half or rugae faint to mostly lacking, entire surface strongly granulate, dull, (9) propodeal spines elongate, slender, acuminate; spines straight in profile, weakly curved inward in dorsal view; length> 2.0× the distance between their bases and length> 1.0× MOD; infraspinal facet weakly coriarious to weakly rugose, moderately shining; propodeal declivity smooth and shining, and (10) metasternal process large, about twice as long as high, apex more or less flat, translucent in profile ( Figures 20–22 ).

Measurements. lectotype (n = 125). HL 1.70 (1.15–1.85); HW 1.61 (1.08–1.86); MOD 0.34 (0.26–0.45); OMD 0.37 (0.32–0.53); SL 1.48 (1.02–1.63); PNW 1.06 (0.65–1.21); HFL 1.90 (1.28–2.14); ML 2.25 (1.45–2.48); PW 0.31 (0.22–0.40); PPW 0.51 (0.34–0.61). Indices: SI 91.93 (72.12–100.93); CI 94.71 (88.52–111.97); OI 21.12 (18.39–25.42); HFI 118.01 (90.51–127.34).

Queen diagnosis. This caste is diagnosed by the following combination of features: (1) color variable: mostly concolorous medium to dark brown to brownish-black, legs and gaster usually orangish-brown or mostly concolorous ferrginous orange except for brownish katepisternum and mesoscutum (mesoscutum sometimes partly orangish), gastral terga with transverse blackish band along posterior margins, (2) medial lobe of clypeus with two to three submedial and sublateral, longitudinal rugae, (3) mandibles with 8 teeth, (4) dorsal base of scape weakly flattened; maximum basal width of scape less than maximum preapical width, (5) OMD distinctly less than MOD, (6) cephalic dorsum shining between fine, longitudinal rugae, medial rugae continuing to posterior margin or medial rugae diverging toward posterior margin with fine, transverse to arcuate rugae along posterior margin; longitudinal rugae above and below eyes; (7) psammophore well developed, (8) sides of pronotum weakly to moderately punctulate between mostly longitudinal rugae; mesoscutum and mesoscutellum smooth and shining with scattered piligerous punctures, mesocutum often with faint longitudinal rugae posterad, mesoscutellum with faint rugae along anterior and/or lateral margins; anepisternum weakly to moderately punctulate, weakly shining, between fine, longitudinal rugae; katepisternum shinier, rugae weaker, rugae sometimes absent along anteroventral margin; sides of propodeum moderately punctate, weakly shining between coarser longitudinal and oblique rugae, (9) propodeal spines elongate, acuminate, weakly recurved in profile, length greater than width at base and less than the distance between their bases; infraspinal facet and posterior declivity weakly to moderately coriarious, weakly shining to shining, and (10) metasternal process large, about twice as long as high, apex more or less flat, translucent ( Figures 23–24 ).

Measurements. (n = 13). HL 1.76 – 2.05; HW 1.80 – 2.03; EL 0.46 – 0.54; OMD 0.36 – 0.45; SL 1.45 – 1.66; HFL 1.72 – 2.27; ML 2.97 – 3.51; PW 0.34 – 0.53; PPW 0.67 – 0.79. Indices: SI 74.36 – 87.57; CI 97.89 – 107.73; OI 24.10 – 27.84; HFI 88.21 – 119.25.

Male diagnosis. This caste is diagnosed by the following combination of features: (11) blackish brown, gaster and appendages brown, (12) clypeus weakly convex in profile, anteromedial margin of medial lobe concave with a small, narrow, medial excision, (13) mandibles with 2, rarely 3, small triangular denticles or teeth basad of preapical tooth, (14) anterior ocellus above level of top of eyes, (15) anepisternum with wavy longitudinal rugae or rugae restricted to dorsad portion, interrugae weakly to moderately coriarious, dull to weakly shining, areas lacking rugae usually lineopunctate-granulate; katepisternum shinier, lacking obvious rugae, weakly to moderately coriarious with ventral margin usually less coriarious and shinier than rest of katepisternum, (16) propodeum contiguously punctate, with scattered short, irregular, fine, oblique rugae; teeth or spines absent, (17) metasternal process about twice as long as tall, apex mostly flat with anterior and posterior corners broadly rounded, and (18) subpetiolar process absent to low and obtuse ( Figures 1D , 25 ).

Measurements. (n = 4). HL 0.99–1.08; HW 0.92–0.99; MOD 0.39–0.41; OMD 0.14–0.16; SL 0.35–0.43; HFL 1.79–2.01; ML 2.58–2.78; PW 0.33–0.40; PPW 0.66–0.70; AOD 0.10–0.11; IOD 0.31–0.35; OOD 0.31–0.35. Indices: SI 37.89–38.04; CI 87.04–92.93; OI 41.41–42.55; HFI 194.57–204.26.

Additional material examined. MEXICO: Baja California: Bahía de los Ángeles, 10’, Jan 9, 1991 ( RAJC) ; Hwy 1 at 11.65 mi W Bahía de los Ángeles, Mar 9, 1992 ( RAJC) ; 16 km W Bahía de los Ángeles, 450 m, Mar 29, 2012 ( UCDC) ; Hwy 1 at 2.8 mi N turn to Bahía de los Ángeles, Feb 19, 1994 ( RAJC) ; 14 km ENE Jct Hwy 1 and Road to Bahía de los Ángeles, 480 m, Apr 6, 1998 ( UCDC) ; 11.5 mi S Bahía de los Ángeles, Mar 9, 1992 ( RAJC) ; 16.5 km E Hwy 1 on turnoff road to Bahía de los Ángeles, Feb 1, 1995 ( RAJC) ; 19.85 mi S Bahía de los Ángeles, Mar 9, 1992 ( RAJC) ; 29.7 mi SSE Bahía de los Ángeles, 260’, Feb 4, 1995 ( RAJC) ; 48.5 mi S Bahía de los Ángeles, 250’, Mar 6, 1998 ( RAJC; UCDC) ; 4.3 mi NE Pozo Alemán , 1120’, Feb 2, 1996 ( RAJC) ; 0.5 mi E San Ignacio , 1000’, Feb 2, 1995 ( RAJC) ; 0.6 mi N El Progresso , Mar 9, 1992 ( RAJC) ; 5 mi W El Progreso , Mar 8, 1992 ( RAJC) ; 14.7 mi NW El Progreso , 960’, Mar 9, 1992 ( RAJC) ; 14.9 mi NE El Progreso , 700’, Jan 29, 1995 ( RAJC) ; 1.3 mi SW Campo El Faro site, 300’, Jan 25, 1995 ( RAJC) ; 10.5 mi NE El Arco , Mar 8, 1992 ( RAJC) ; 22.25 mi NE El Arco , Mar 8, 1992 ( RAJC) ; 6.5 mi N Las Arrastras de Arriola , 1000’, Feb 9, 1994 ( RAJC) ; Misión Calamalli (at 6.3 mi N El Arco), Mar 8, 1992 ( RAJC) ; San Luis Wash at 8.5 mi W Misión Calamalli, Mar 8, 1992 ( RAJC) ; Vado las Lamparas, 620’, Feb 15, 1997 ( RAJC) ; 4.2 mi W Hwy 1 on road to Santa Rosalita, Feb 29, 1992 ( RAJC) ; 1 mi N of N end Bahía Falsa , 30’, Mar 22, 2001 ( RAJC; UCDC) ; S end Laguna Chapala, 2050’, Mar 10, 2003 ( RAJC; UCDC) ; 2.0 mi E La Chocera, 40’, Mar 10, 2002 ( RAJC; UCDC) ; Bahía San Quintin , 5’, May 1, 1952 & May 21–22, 1952 ( LACM; USNM) ; Bahía Colonet (as Collnet Bay ), no date ( LACM) ; El Consuelo, no date, 1969 & Aug 23, 1977 ( LACM) ; 6 mi NW Rancho Santa Ynez, 1800 ’, Jan 24, 1976 & Apr 5–12, 1977 ( CIDA) ; S end Isla Smith (= Isla Coronado), 10 m & 30 m, Feb 10–11, 1997 ( UCDC) ; Isla Ventana, Mar 10–May 10, 1999 ( UCDC) ; Puerto don Juan at 11 km E Bahía de los Ángeles, 10 m, Feb 12, 1997 ( UCDC) ; Catavina, 550 m, Feb 14, 1997 ( UCDC) ; 14 km S Rosarito , 40 m, Apr 8–9, 1998 ( UCDC) ; 6.2 mi E Rosarito , Jul 10, 1979 ( UCDC) ; 38 km WNW San Ignacio , 90 m, Apr 13, 1998 ( UCDC) . Baja California Sur: Hwy 18 at 7.9 mi SE El Arco, 440’, Jan 28, 1995 ( RAJC) ; 21.4 mi S San Ignacio , Mar 7, 1992 ( RAJC) ; 15 mi N San Ignacio , May 24, 1938 ( LACM; USNM) ; 50 km SSW San Ignacio , 5 m, Jan 4, 1990 ( UCDC) ; nr Rancho Esperanza, 8.8 mi S San Ignacio, 4.3 km N KP 59.5, Sep 7, 1985 ( LACM) ; 45 mi N San Ignacio , Jul 27, 1938 ( USNM) ; Hwy 1 at 7.8 mi S Santa Rosalía, Feb 29, 1992 ( RAJC) ; 17 mi W Santa Rosalía, Jun 18, 1967 ( LACM) ; 10 km S Santa Rosalía, 1800 ’, Oct 4, 1975 ( LACM; UAIC) ; Boca Magdalena ( Hwy 1 at 21.7 mi S Santa Rosalía ), 200’, Feb 29, 1992 ( RAJC) ; 0.5 mi S San Gregorio , Mar 5, 1992 ( RAJC) ; 1.8 mi E Río San Gregorio , Mar 6, 1992 ( RAJC) ; 3.05 mi E San Gregorio , Mar 4, 1992 ( RAJC) ; 1.2 mi E Hwy 1 on road to Sierra San Francisco, 200’, Jan 27, 1995 ( RAJC) ; Jct Hwy 1 & Rd to Sierra San Francisco, 180’, Mar 13, 2003 ( RAJC) ; 1.8 mi W Hwy 1 on road to San Isidro , Mar 2, 1992 ( RAJC) ; 13.5 mi W Hwy 1 on road to San Isidro , Mar 2, 1992 ( RAJC) ; 5.05 mi NE San Isidro , Mar 2, 1992 ( RAJC) ; 10.9 mi SE Vizcaíno , 120’, Jan 26, 1995 ( RAJC) ; 25 km W Vizcaíno , 200’, Jan 7, 1991 ( LACM; RAJC) ; 6.9 mi W Vizcaíno , 250’, Jan 26, 1995 ( RAJC) ; 12.5 mi E Bahía Tortuga , 220’, Mar 8, 1998 ( RAJC; UCDC) ; 1 mi E Rancho San José Magdalena , Feb 15, 1993 ( RAJC) ; 4.9 mi SE San Juanico , Mar 6, 1992 ( RAJC) ; 7.4 mi N San Juanico , Mar 6, 1992 ( RAJC) ; base of Cerro las Mulas, Feb 17, 1993 ( RAJC) ; Cerro las Mulas, May 10, 1992 ( RAJC) ; Cabo San Lucas, 140’, Feb 2, 1996 ( RAJC) ; Hwy 1 at 15.1 mi E Guamúchil, Feb 29, 1992 ( RAJC) ; Hwy 1 at 20.6 mi E Guamúchil & 4 mi S Volcán Tres Vírgenes, Feb 29, 1992 ( RAJC) ; Hwy 1 at 8.3 mi E Guamúchil (in Santa María Wash ), Mar 2, 1992 ( RAJC) ; Santa María Wash at 0.2 mi S Hwy 1 (6.3 mi E Guamúchil ), Mar 28, 1992 ( RAJC) ; Hwy 1 at 19.5 mi S Ciudad Constitución, 120’, Jan 31, 1998 ( RAJC) ; Hwy 22 at 6 mi W Ciudad Constitución, 50’, Feb 4, 1996 ( RAJC) ; Hwy 1 at 3.5 mi S Mulegé, Feb 29, 1992 ( RAJC) ; Hwy 1 at 20.5 mi S Mulegé, Mar 1, 1992 ( RAJC) ; Hwy 1 at 27.3 mi SE border of Baja California, 100’, Feb 28, 1992 ( RAJC) ; Hwy 1 at 37.3 mi SE border of Baja California ( 10.6 mi NW Gustavo Diaz Ordaz ), Mar 28, 1992 ( RAJC) ; Hwy 1 at 3.3 mi E Ejido Alfredo V. Bonfil, Feb 12, 1993 ( RAJC) ; Hwy 1 at 6.05 mi S Gustavo Diaz Ordaz (53.95 mi S border Baja California), Mar 28, 1992 ( RAJC) ; Hwy 53 at 21.7 mi N Villa Insurgentes, Mar 2, 1992 ( RAJC) ; Hwy 1 at 43.6 mi NW Villa Insurgentes, 1430’, Mar 14, 2002 ( RAJC) ; Hwy 53 at 22.4 mi N Ejido Francisco Villa (at turnoff to Comondú), Mar 2, 1992 ( RAJC) ; Hwy 53 at 3.8 mi N Ejido Villa Francisco (at turnoff to Comondú), Mar 2, 1992 ( RAJC) ; Hwy 53 at 5.5 mi NE Ejido Francisco Villa (at turnoff to Comondú), Mar 3, 1992 ( RAJC) ; La Purísima, Mar 2–3, 1992 ( RAJC) ; Hwy 1 at 4.0 km S Jct to Santiago, 520’, Mar 19, 2014 ( RAJC) ; Hwy 1 at turnoff to Ribera, 240’, Mar 21, 2014 ( NHMW; RAJC) ; E of Punta Chele , May 21, 1992 ( RAJC) ; La Paz, Sept 4, 1959 ( LACM) ; Hwy 1 at 11.0 mi S La Paz, 520’, Mar 16, 2002 ( RAJC) ; Ramal el Chivato, S of El Cien , Sep 17, 1983 ( LACM) ; Loreto , Feb 1923 ( LACM; USNM) ; 2 km N Loreto , 5 m, Dec 20, 2015 ( MMPC) ; 6 mi N El Triunfo , Jul 15, 1938 ( USNM) ; 4 km ESE Guerrero Negro, 10 m, Jan 2, 1990 ( UCDC) ; 2.2 mi N Rancho Caracol , 500 m, Jul 11–12, 1999 ( UCDC) ; Juncalito, 5 m, Jul 13, 1995 ( UCDC) . Locations not found: Baja California Sur: Virgen María, Jan 25, 1967 ( LACM) ( Figure 27A ).

Etymology. Pergande did not indicate the derivation of the specific epithet, julianus , but it seems likely that it referred to the type locality “San Julio”, given that Julian is Julio.

Discussion. Veromessor pergandei and V. stoddardi are the only congeners that might be sympatric with V. julianus . Veromessor julianus cannot be confused with either species, and it is diagnosed by: (1) well developed psammophore, (2) long propodeal spines (> 2× longer than distance between their bases), and (3) metasternal process about twice as long as high, apex more or less flat, translucent in profile. This species is recognized in the field based on their large colonies (> 40,000 workers) that forage in long columns from near dusk and into the night ( Creighton, 1953; Johnson, 2000 a, 2000b). Veromessor julianus may be sympatric with V. andrei near Bahía San Quintin, but the former species is easily distinguished by its well developed psammophore; the psammophore is poorly developed in V. andrei .

Wheeler and Creighton (1934) described V. julianus subsp. clarior because it differed from the typical V. julianus by: (1) having a more quadrate head, (2) shorter antennal scapes that just reach the posterior margin, (3) mesopropodeal suture notably impressed dorsally, (4) propodeal spines longer, thinner, and more elevated meeting the plane of the basal surface of the propodeum at 45 o, (5) cephalic striae finer, and (6) granulation on the mesosoma much less pronounced. They also noted that julianus subsp. clarior was much more hairy than the typical julianus , especially in regard to the gular ammochaetae and abdominal hairs, and with a clear, yellowish-red color, the gaster piceous brown, usually with a yellowish spot at the base of the first segment.

In the same paper, Wheeler and Creighton (1934) described the other subspecies, V. julianus subsp. manni , as having an impressed mesopropodeal suture (as in subsp. clarior ), but differing from subsp. clarior in its smoother cephalic sculpture, with striae scarcely visible in smaller workers, but the propodeal spines were more similar to those in the typical julianus . Color less clear than that of clarior, with the head tending toward a muddy, brownishred, and the yellowish spot at the base of the first gastral tergum reduced or absent. Veromessor julianus subsp. manni was also smaller than the typical julianus and julianus subsp. clarior , but the authors noted that these size differences may not remain after examining additional specimens.

All three subspecies of V. julianus were described from few workers such that the authors examined little variation within each subspecies. Numerous series now are available so that subspecies variation can be examined, and these series demonstrate that all of the above characters described to separate these forms vary within a nest series. For example, Wheeler and Creighton (1934) noted that the mesopropodeal suture was impressed on V. julianus subsp. clarior and V. julianus subsp. manni , but that the suture was not impressed in V. julianus . Examination of long nest series demonstrates that the mesopropodeal suture is impressed below the level of the propodeum in some workers, but not impressed in others, such that there is no consistent variation across subspecies.

As noted in the above discussion regarding the subspecies, workers of V. julianus have two color forms: (1) bicolored, with an orangish head and mesosoma and a darker gaster, and (2) dark brown with the head often slightly darker than the mesosoma. Workers within a colony generally consist of one color form, but workers with the alternate color are present occasionally. In combination with lack of morphological differences between the two subspecies, bivariate plots for several morphological characters display similar allometries for both color forms ( Figure 26 ). Both color forms also occur in proximate locales on the peninsula.

Queen color correlates with worker color in the dark brown form as colonies with dark brown workers contain concolorous dark brownish queens. Alternatively, colonies with bicolored workers (orangish head and mesosoma, brownish gaster) contain orangish queens and sometimes concolorous brownish queens indicating that these two color forms are not consistent for alate queens.

Our molecular phylogeny indicates that the color forms belong to two clades. We then conducted preliminary molecular species delimitation analyses using STACEY ( Jones, 2017) and DELINEATE (Sukumaran, Holder, & Knowles, 2021), which consistently show V. julianus lineages to be a single species (M.L. Borowiec, unpub. data). We leave a more comprehensive exploration of possible divergence among these lineages to our phylogenetic study (M.L. Borowiec, unpub. data) but note here that more definitive conclusions will require additional sampling, including more samples of intermediate phenotypes. Here, we consider V. julianus subsp. clarior and V. julianus subsp. manni to be junior synonyms of V. julianus , and we synonomize both subspecies under V. julianus .

Wheeler and Creighton (1934) misspelled the type locality for V. julianus subsp. clarior as Commondu, Lower California; the correct spelling is Comondú (= San José de Comondú), which is in Baja California Sur, Mexico. For V. julianus subsp. manni, Wheeler and Creighton (1934) gave type locality as “Purissima, Lower California ”, collected by W.M. Mann. However, no type material was located from “Purissima” and we believe their original citation to be spurious. We did locate two workers collected at Las Parras, Baja California, by W.M. Mann [USNM] with the additional label “not a syntype?, M. R. Smith”. We believe that Las Parras is the correct type locality, such that both of these workers are syntypes of V. julianus subsp. manni . We designated the bottom worker as a lectotype and placed such a label on the pin. Las Parras is a few miles west of Loreto.

Biology. Nests of V. julianus occur in open sites. Colonies of V. julianus have not been censused, but observations indicate that they contain tens of thousands of workers. Nests consist of a small tumulus lacking chaff to a large disc surrounded by chaff; nests sometimes have multiple entrances ( Creighton, 1953; R.A. Johnson, pers. obs.). Workers of V. julianus forage in columns with workers fanning out to forage at the distal end of the column; workers clear a narrow trail through vegetation when necessary ( Creighton, 1953; Johnson, 2000b). During winter and spring, foraging columns of V. julianus form prior to dusk, and foraging continues into the night with workers returning early the next morning ( Johnson, 2000a), and it appears to forage during the day in at least some parts of its range ( Creighton, 1953). Workers are weakly polymorphic.

Gland chemistry has not been examined in V. julianus . Like other large-colony congeners, workers of V. julianus have a large pygidial gland reservoir with a textured tergal cuticle ( Hölldobler et al., 2013).

Mating flights of V. julianus occur in February – March with few sexuals being released over 1 – 2 or more weeks. Flights occur during early morning (8:30 – 10:00 MST) at temperatures from 16–23 o C, and occur during mild breezes or overcast skies, but they were precluded by light rain or moderate breezes ( Johnson, 2000a). Mating appears to occur in the air.

Queens are haplometrotic ( Johnson, 2000a). Dry mass of alate queens averages 11.1 + 0.4 mg. Alate queens contain an average of 47.4 + 1.9 (n = 5) ovarioles, and mated queens contain an average of 1.225 + 0.02 (n = 2) million sperm. Dry mass for virgin males averages 1.9 + 0.2 mg, and they contain an average of 4.4 + 0.17 (n = 3) million sperm (R.A. Johnson, unpub. data). Queens have a relatively low heat tolerance compared to other desert ants with most queens dying in hydrated conditions at 42 o C and all at 43 o C over a 2 h period ( Johnson, 2000a). Ventilation patterns and metabolic rate of workers and alate queens are discussed in Lighton and Berrigan (1995).

Veromessor julianus is a hot desert species that is endemic to the Baja California peninsula of Mexico at elevations from 0–625 m (see Johnson, 2000a; Johnson & Ward, 2002). It is most common in sandy soils but it also occurs on rocky hillsides and bajadas. Veromessor julianus has a parapatric distribution with V. pergandei , with the former species occurring in slightly more mesic microhabitats, i.e., in wetter soils and/or at higher elevations ( Johnson, 2000a; R.A. Johnson, pers. obs.). This species occurs in the Baja California desert, Gulf of California xeric scrub, San Lucan xeric scrub, and Sierra de la Laguna dry forests ecoregions, as defined by Olson et al. (2001) ( Figure 27A ).

Figures

FIGURE 1. Photographs of the metasternal process on males of Veromessor: (A) V. andrei (CASENT4010823), (B) V. chamberlini (UCRC_ENT00500152), (C)V.chicoensis (CASENT0869853), (D) V.julianus (LACMENT359792),(E)V.lariversi (CASENT0761204), (F) V. lobognathus (LACMENT363986), (G) V. pergandei (CASENT0869850), (H) V. pseudolariversi (CASENT0869851), (I) V. smithi (LACMENT364071), and (J) V. stoddardi (LACMENT364102). Photographs by Robert Johnson from www.AntWeb.org.

FIGURE 20. Photograph of Veromessor julianus worker (bicolored form): (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922837). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 21. Photograph of Veromessor julianus minor worker (dark form): (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922836). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 22. Photograph of Veromessor julianus major worker (dark form): (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922835). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 23. Photograph of Veromessor julianus alate queen (light form): (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0923146). Photographs by Wade Lee from www.AntWeb.org.

FIGURE 24. Photograph of Veromessor julianus alate queen (dark form): (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922838). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 25. Photograph of Veromessor julianus male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0923344). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 26. Bivariate plots for workers of the two color forms (bicolored and dark) of Veromessor julianus: (A) head width versus head length, (B) mesosoma length versus pronotum width, and (C) mesosoma length versus eye length. Sample size for each color form is in parentheses.

FIGURE 27. Geographic distribution of: (A) Veromessor julianus, (B) V. lariversi, and (C) V. lobognathus. The larger black circle in each panel denotes the type locality.