Nest Architecture and Population of the Honey Ant, Myrmecocystus mexicanus Wesmael (Formicidae), in Colorado

Abstract

Crater development and dimensions were determined by observing 66 Myrmecocys- tus mexicanus nests in the Garden of the Gods area for periods up to 453 days. Crater develop- ment varies from none to well-constructed cones 68 mm high. Crater dimensions change season- ally and sometimes daily in response to weather conditions and worker activity. The entrance is a large symmetrical opening with a mean diameter of 12 mm, which is likely to be closed after a heavy rain and during the winter. Six double-entrance nests were located. Subsurface architecture and population size were determined from four complete and three partial excavations. The entrance opens into a vertical or oblique passage about 10 cm long before branching into a laby- rinth of horizontal passages and small chambers arranged asymmetrically about it and extending to depths of 20 cm. Only open vertical passage descends from the subsurface labyrinth to domed replete chambers below. Upper replete chambers tend to be smaller, more numerous, and closer together than lower ones. The first repletes, 1 to 12 in number, occur at depths of 17 to 51 cm. Replete chambers per colony vary in number from 7 to 21, and the number of repletes per chamber ranges from 1 to 348. Replete chambers range from 5.1-33 cm in length, 3-24 cm in width, and 1-5 cm in height. Nests ranged from 0.97 to 1.8 m in depth. Each nest houses about 5,000 aqts, of which 22-25% exhibit abdominal distension. The number of repletes in each nest varies from 351 to 1030. The maximum number of winged reproductives is 209 queens and 100- 110 males. One wingless queen is present in each nest. Honey ants are unusual in producing swollen workers called repletes to store the seasonal flow of plant nectar, and their nests exhibit certain archi-