Veromessor pergandei

Messor pergandei is one of the commonest ants in the Mojave and Sonoran deserts. It is especially noteworthy because of (1) its glistening black color (which is unexpected in a hot dry climate); (2) its strong polymorphism, which is not shared by any of its Nevada congeners; (3) its large craters with their huge chaff piles, which are such conspicuous features of the desert landscape; and (4) its foraging column. (Wheeler and Wheeler 1986)

Distribution
Deserts of southwestern Arizona, southern Nevada, southeastern California, western Sonora, and northern Lower California.

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

Biology
Wheeler and Wheeler (1986) :

A typical nest is in an exposed area and is surmounted by a low circular or semicircular crater of excavated soil, which is 30 cm in diameter. There is a single large (16 mm) entrance in the throat of the crater. The chaffpile - a mass of discarded husks from the harvested seeds, other rubbish and a goodly number of viable seeds-forms a crescentic or circular zone at the periphery of the crater. Well-established colonies usually have several craters, often in a cluster but sometimes scattered over an area 3-4 m in diameter. Two or more craters may be active. New craters are opened from below and lack a chaff pile. Extinct craters have the entrance closed and the chaff pile is matted down by the weather.

The following account of foraging is adapted from Creighton's admirable 1953 account. In late spring and early summer pergandei starts its daily routine before sunrise. The workers emerge from the entrance and move very slowly (because of the low temperature) over the crater. After sunrise these movements are accelerated. Thirty to 45 minutes after sunlight first strikes the nest a foraging column pushes out from the crater and moves decisively toward the seed supply, which may be 70 or more meters from the nest. Naturally at first all workers are outward bound. Soon, however, homeward bound seed-carriers appear in the column. After 2 or 3 hours (i.e., about midmorning) workers suddenly cease to leave the nest. The column disappears as soon as all the homeward bound workers have reached the nest.

Nest work follows. Workers emerge from the entrance each bearing a piece of gravel, which is dropped on the crater, or a seed husk, which is deposited on the chaff pile. Nest work usually continues until the second foraging period in the late afternoon. But on very hot days all ants disappear into the nest in the early afternoon. In the late afternoon nest work increases suddenly and nest workers soon cover the crater. Then out of the entrance there is a rush of workers carrying nothing, who leave the crater and start a foraging column. Foraging continues until early dusk (i.e., for about 3 hours). Nocturnal nest work may continue until early morning.

Nevada, Wheeler and Wheeler (1986) - In winter foraging may be limited to the middle of the day. The following notes result from the month we spent studying this species at Boulder City: (1) In hot weather some foraging may be done at night, either by moonlight or in total darkness. (2) The width of one observed column increased from 2 cm to 107 cm and then narrowed to 30 cm depending upon the terrain and the plant obstructions. (3) More than one column may operate simultaneously from the same nest, or even from the same entrance. (4) No one has ever counted the population of a pergandei colony. This would probably be an impossible task, considering the rocky terrain which the species inhabits. Some idea of its enormity may be grasped from an estimate of I7,000 workers in a column 40 m long (J. Wheeler and Rissing, 1975b). (5) The longest column we have measured was 46 m. (6) We have clocked the speed of workers in a column from 5 mm/sec at 16°C to 66 mm/sec at 42°C soil surface temperature. The largest crater we have measured was at Davis Dam in Clark Co.: 2 m in diameter; a nearby crater was 1 m and there were numerous other very large craters in the vicinity. We have 48 records from 33 localities, all in the Hot Desert in the southern fourth of the state; 600-4,000 ft.

Nomenclature

 *  pergandei. Aphaenogaster pergandei Mayr, 1886d: 448 (w.) U.S.A. Wheeler, W.M. & Creighton, 1934: 376 (s.q.m.); Wheeler, G.C. & Wheeler, J. 1972b: 240 (l.). Combination in Stenamma (Messor): Emery, 1895c: 307; in Novomessor: Emery, 1915d: 73; in N. (Veromessor): Forel, 1917: 234; in Veromessor: Wheeler, W.M. & Creighton, 1934: 374; in Messor: Bolton, 1982: 341. See also: Smith, D.R. 1979: 1365.