Myrmecocystus flaviceps

A nocturnal foraging species that is known to gather nectar from plants and solicit aphids. Workers also gather remnants of dead arthropods. Nests have larger diameter craters (> 6 inches) and large entrance holes (> 1/2 inch).

Identification
The only member of the flaviceps group of the Myrmecoystus subgenus Endiodioctes.

Key to Myrmecocystus subgenus Endiodioctes species.

Worker - Malar area with twelve or fewer erect hairs; pronotal hairs short, stiff; third tergum with abundant appressed pubescence; gaster uniformly brown, without mediobasal yellowish blotches on first and second terga; CI usually (over 80%) in excess of 90; mandible septemdentate. Female; penultimate segment of maxillary palp slender, approximately parallel sided; punctures of parapsis variably spaced, of two sizes; discs of second and third terga very sparsely punctate and sparsely pubescent; fore femur with few or no erect hairs on inner and dorsal faces, the outer and ventral faces with abundant long hairs; malar area with numerous erect hairs. Male: ventral lobe of aedeagus convex in profile; posterior half of mesoscutum wholly or partly polished; first two terga with abundant appressed pubescence; occipital hairs always less than 0.75 X MOD; HW less than 0.8 mm. (Snelling 1976)

Distribution
United States, Mexico. Southwestern Utah and southern Nevada to northern Sonora and central Lower California.

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Mexico.

Habitat
Juniper Steppe Woodland, Great Basin Sagebrush, Saltbush-Greasewood, Creosote bush, Creosote bush-Bur sage, and Palo Verde-Cactus shrub communities.

Biology
Snelling (1976) - Wheeler (1912) noted that craters of this ant were about 6-8 in. in diameter with entrances nearly 0.5 in. across. The nest crater figured by Wheeler (1908:367, Fig. 14) as that of mimicus from Needles, California, probably belongs to this species. Wheeler and Wheeler (1974), studying this ant at Deep Canyon, California, figured two nest craters. They reported 38 samples from the Desert Biome: Larrea-Palo Verde, 12; Cholla-Palo Verde, 25; Agave-Ocotillo, I. The nests which they observed were larger than those noted by Wheeler, the craters 10-16 in. in diameter (but the one in figure 44 does not seem nearly so large) with entrances 1.5-3.0 in. across. Alate females were found in the nests on 1 December.

Participation in a biocenose on Opuntia echinocarpa was observed by Wheeler and Wheeler. Other insects noted to be present were: "... mealybugs, aphids, other ants (Solenopsis xyloni), and braconids [Lysiphlebus testaceus (Cresson)] ..." They further noted workers of this ant at extrafloral nectaries of Euphorbia micromera.

The ant is a diurnal forager, primarily as a scavenger-predator. Considerable quantities of nectar are taken from floral and extrafloral nectaries as well as indirectly through solicitation of mealybugs and aphids. Repletes were found in colonies near Shorty's Well, Death Valley.

Creighton found the species flying after a light rain on 16 Feb. 1963 near Thousand Palms, California.

Nomenclature

 *  flaviceps. Myrmecocystus yuma var. flaviceps Wheeler, W.M. 1912d: 177 (w.) U.S.A. Snelling, R.R. 1976: 84 (q.m.). Raised to species: Creighton, 1950a: 443.

Snelling (1976) - Wheeler originally described this as a variety of Myrmecocystus yuma, but noted that it would perhaps ultimately rank as an independent species. The abundance of differences, which here place the two in different subgenera, more than justifies that assumption.

When Creighton (1950) elevated Myrmecocystus flaviceps to full species he apparently did so because it and yuma were known to be sympatric. There is no evidence that he knew either from other than their type series and in the case of flaviceps the types are in very poor condition. Creighton separated the two on the basis of head shape and color.

The type series consists wholly of minor and media workers, some of them callow, and is exceptionally poorly mounted. I have been able to examine about two dozen of these specimens and between them have accumulated the characters permitting the present interpretation. As now understood, this is a western form allied to Myrmecocystus romainei which replaces that species in low desert areas. It is a variable species, and possibly the present interpretation is too conservative.

There is some variation in the size of this species, other than the normal polymorphic variation. Workers from Calmalli and 26.9 mi S of El Arco, in Lower California, are the largest examples seen. The head length of the larger workers from these series is in excess of 1.4 mm. In these large individuals, the sides of the head are strongly convex, the head approaching the orbiculate condition of Myrmecocystus placodops and Myrmecocystus intonsus. Large workers from a sample collected 35 mi S of El Marmolito, Baja California, have the head length somewhat less (about 1.3 mm), but still retain the semiorbiculate shape.

By contrast, specimens from more northern stations tend to be distinctly smaller. Samples from California yield the following maximum head length: 1.25 mm (Midway Well, Death Valley; Shaver's Well, Riverside Co.), 1. 18 mm (Granite Mts., San Bernardino Co.), 1.15 mm (Coon Hollow, Riverside Co.) and 1.05 mm (Marble Mts., San Bernardino Co.). In these more northern samples the sides of the head, even in the largest workers, are straight or but slightly convex. Rarely are individuals with suborbiculate heads encountered.

The pattern of erect hairs is subject to great variation. The samples from central Lower California generally have six, or fewer, hairs on the malar area in frontal view. The scape hairs are numerous and at right angles to the long axis of that segment. The fore femur has numerous short erect hairs on the anterior face. The seta count for the hind tibia is in excess of 30. The cotypes from Yuma, Arizona, are similar but the hairs of the scape are finer, and are mostly reclinate; the fore femur is without erect hairs on the anterior face. The hind tibia have far fewer erect hairs, the seta count ranging from 15-20. Specimens from the Granite Mts. have 10 or more erect hairs on the malar area, the fore femur with numerous hairs on the anterior face and a seta count of 30 or more for the hind tibia. The few specimens from Sonoyta, Sonora, have the scape setae exceptionally fine; many of these are subappressed and it is difficult to achieve a meaningful seta count. In this sample the fore femur lacks erect hairs on the anterior face and the setae of the hind tibia are from 12-18.

Although the third tergum typically is uniformly covered with fine appressed pubescence, producing the characteristic gastric sheen, this is by no means con-stant. A few of the smallest workers from El Arco and Calmalli have the pubescence greatly reduced and it is absent (save a few widely scattered hairs) in the majority of the sample from El Marmolito.

The color of this species is quite variable. Southernmost samples from Lower California have the head and thorax brownish-red, the propodeum, legs and petiole darker; the infuscation sometimes extends over the entire thoracic dorsum and the top of the head. Specimens from Bahia San Luis Gonzaga, Baja California, are very extensively infuscated. The head, thorax and legs are light reddish in specimens from Shaver's Well, with the propodeum and petiole slightly darker. Samples from Death Valley have the head, thorax and legs light reddish, brighter than those from Shaver's Well, with only the petiole a little darker.

Workers of Myrmecocystus flaviceps from the Mojave Desert are very similar to those of romainei from Utah and central Arizona. The characteristic punctation of the vertex of Myrmecocystus romainei become weaker and sparser than in the more eastern populations of that species. They may be confused with flaviceps. In general, flaviceps workers from the Mojave Desert have twelve or fewer erect hairs on the malar area. There is, however, sufficient variation to make this character uncertain.

The erect pronotal hairs of flaviceps seem consistently less than 0.5 x MOD. In romainei there is less constancy, but those populations in which the hairs are 0.5, or less x MOD are eastern. The specimens from Utah and central Arizona have longer hairs, 0.57-0.62 x MOD.

Worker
Snelling (1976) - Measurements. HL 0.83-1.23 (0.95); HW 0.73-1.23 (0.87); SL 0.97-1.43 (1.07); WL 1.23-1.80 (1.27); PW 0.53-0.87 (0.57).

Head: Longer than broad in small workers to slightly broader than long in largest, CI 87-103 (91), over 90 in more than 80% of samples; HL less than SL, SI 108-129 (123); in frontal view broadest at or below lower eye margin, sides straight or barely convex, little or not at all convergent toward mandibular insertion. Occiput, in frontal view, evenly rounded from side to side, without lateral corners. Eye small, 0.75-0.83 (0.75) x first flagellomere; OMD 1.38-1.88 (1.63) x EL. Mandible usually with seven teeth, range: 6-8.

Thorax: Slender to moderately stout, PW 0.41-0.49 (0.45) x WL; mesonotum evenly sloping to metanotum. Propodeum higher than long; in profile, juncture of basal and posterior faces broadly rounded.

Petiole: In profile, bluntly cuneate, summit broadly rounded; crest, from behind, fiat or slightly convex, without median notch.

Vestiture: Cephalic pubescence dilute, producing weak sheen on malar area and frons, more pronounced on occiput; pubescence moderately dense on thorax; denser on first three terga.

Malar area, in frontal view, with twelve or fewer fine, erect hairs; longest occipital hairs about 0.5 x MOD; pronotal disc with 10-14 short, erect hairs, longest 0.5, or less, x MOD; mesonotum with about 12 short, erect hairs dorsally, longest less than 0.5 x MOD; propodeum with about an equal number on basal face; crest and sides of petiole with a few very short, erect hairs. First three terga with sparse discal hairs which are shorter than apical width of hind tibia, hairs longer on apical margins, succeeding segments and on sterna. Short, erect to subdecumbent hairs numerous on anterior and lateral surfaces of scape, all femora (except inner face of fore femur) and extensor surface of tibiae.

Integument: Head lightly shagreened and shiny, with close micropunctures on frons and frontal lobe; coarser and sparser on occiput. Thoracic dorsum moderately shiny, slightly and closely shagreened, sides and propodeum duller. First three terga slightly shiny, closely shagreened and micropunctate.

Color: Normal: Head, thorax and appendages yellowish-ferruginous, head a little darker on frons and occiput; gaster light to medium brownish. Baja California: Frons, occiput, thorax and gaster dark brownish; clypeus, mandible and malar area yellowish; legs medium brownish.

Queen
Snelling (1976) - Measurements. HL 1.47-1.63; HW 1.57-1.73; SL 1.37-1.53; WL 3.4-3.8; PW 1.9-2.5.

Head: Slightly to distinctly broader than long, CI 102-111, longer than to as long as scape, SI 90-100; malar area, in frontal view, barely convex, not notably convergent toward mandibular insertion. Occiput, in frontal view, gently convex, lateral corners broadly rounded. Eye small, 1.00-1.45 x first flagellomere; OMD 1.46-1.73 x EL. OOD 4.00-4.34 x OD; IOD 2.66-3.33 x OD. Mandible with seven to nine, usually eight, teeth. Penultimate segment of maxillary palp approximately parallel-sided, not notably narrowed at base or apex.

Thorax: Robust, PW 0.53-0.69 x WL. Posterior half of mesoscutum, scutellum and metanotum flattened, in profile, forming a continuous slope to base of propodeum. Propodeum, in profile, usually evenly, gently convex, without defined basal and posterior faces; rarely with basal and posterior faces distinct.

Petiole: Sharply cuneate in profile, summit narrow; in frontal view, crest weakly to strongly angularly incised.

Vestiture: Cephalic pubescence moderately dense on occiput, lighter on frontal lobes and malar area, sparse elsewhere. Thoracic pubescence sparse on mesoscutum and scutellum, dense elsewhere. Gastric pubescence moderately dense basally and on sides of terga, but with broad median areas of first four segments very sparsely pubescent.

Side of head, in frontal view, with six or more long, slender flexuous hairs; occipital hairs erect, slender, longest less than MOD. Mesoscutum with sparse erect hairs, longest less than MOD; scutellum with sparse erect hairs, some of which are about equal to EL; pleura with scattered erect hairs similar to those of scutum. Propodeum with scattered erect hairs on all surfaces, longest less than MOD. Petiole with short erect hairs on sides and crest. Terga with sparse, short erect hairs, those of margins not conspicuously longer than those of discs; hairs of fifth tergum longer than those of first four segments. Scape with scattered short, suberect hairs on all except inner face and abundant shorter subdecumbent hairs. Fore femur with abundant long, erect hairs on ventral and outer faces, none on inner and dorsal faces; mid and hind femora and all tibiae with abundant short subdecumbent to erect hairs. Hind wing with fringe hairs along posterior margin.

Integument: Cephalic surfaces shiny; sides of clypeus irregularly, lightly shagreened and with scattered coarse punctures; malar area with abundant, fine, often elongate, punctures of variable size; frontal lobes with punctures irregularly spaced, often with impunctate areas, punctures of two sizes; frons with extensive impunctate areas on either side of midline, otherwise with sparse, fine punctures; occiput closely, finely micropunctate and with scattered coarser punctures. Scutum shiny, with scattered coarse punctures, sparser in middle; parapsis with punctures irregularly spaced and of two sizes. Median area of scutellum sparsely punctate, marginal areas more finely and closely punctate. Pleura slightly shiny, anepisternum a little more coarsely and less closely punctate than katepisternum. Propodeum dull, closely shagreened. Four basal terga moderately shiny on discs, lightly shagreened and with only sparse setigerous punctures.

Color: Head dark ferruginous with infuscated occipital and frontal areas; thorax dark brownish; gaster dark brown to blackish, with margins of segments yellowish; appendages medium brownish. Wings whitish, veins and stigma yellowish to brownish yellow.

Male
Snelling (1976) - Measurements. HL 0.68-0.80; HW 0.70-0.80; SL 0.77-0.93; PW 0.77-1.10; WL 1.50-1.90.

Head: Longer than broad to slightly broader than long, CI 96-102; distinctly shorter than scape, SI 108-123; in frontal view, malar margins straight, distinctly convergent toward mandibular insertions; occipital margin evenly convex, without defined lateral angles. OMD 0.67-1.00 x EL; 000 2.50-3.50 x OD; IOD 3.00-3.50 x OD. Mandible without preapical notch, cutting margin edentate.

Thorax: Moderately robust to robust, PW 0.51-0.64 x WL. Propodeum without clearly defined basal face.

Petiole: Thick in profile, bluntly cuneate; crest, in frontal view, narrowly, shallowly, angularly incised.

Vestiture: Pubescence sparse on head and thorax, denser on propodeum; very scattered on first tergum, more conspicuous, but still sparse, on next three segments.

Cephalic pilosity fairly abundant, usually with about six hairs in malar area in frontal view; occipital hairs fine, longest less than half MOD. Mesoscutal hairs sparse, longest less than 0.5 x MOD; scutellar hairs sparse, longest a little less than MOD; pleural hairs sparse, none longer than 0.5 x MOD; propodeum with scattered hairs on side and across base, longest about 0.5 x MOD. Petiole with sparse short hairs on side and crest. Gaster with sparse, long, slender hairs, longest not exceeding MOD. Scape with abundant suberect to erect hairs, much sparser, or absent, from posterior face. Femora with suberect to erect hairs on all surfaces; tibiae with short, sparse, suberect hairs on extensor surface, finer, shorter, subdecumbent hairs elsewhere. Posterior margin of hind wing with fringe hairs.

Integument: Head moderately shiny, lightly shagreened, nearly smooth on vertex; with scattered fine setigerous punctures. Discs of scutum and scutellum shiny, lightly shagreened, usually with polished median areas of irregular extent, and with scattered setigerous punctures; pleura slightly shiny, closely shagreened and with sparse setigerous punctures. Middle of propodeum smooth and shiny, segment otherwise closely shagreened and slightly shiny. Gastric segments moderately shiny, lightly shagreened, median areas of terga one to three often subpolished.

Color: Medium to dark brownish, gaster sometimes more yellowish (callows?); flagellum, mandibles and legs lighter. Wings whitish, veins and stigma yellowish to brownish yellow.

Type Material
Snelling (1976) - Wheeler 1913: "Described from numerous workers taken from several colonies at Yuma, Arizona ..." Lectotype, by present designation, agreeing with the above worker description and parenthetical figures: Yuma, Ariz., 26 Nov. 1910, W. M. Wheeler, in. Lectoparatype workers with same data in AMNH,,.