In the vicinity of Douglas, Arizona, male Protoxaea gloriosa were noted establishing territories as early as July 16, 1962, although the principal emergence of both sexes occurred on July 26 and 27, following the first soaking summer rains. The territories involved flowering plants which were guarded during the morning hours, primarily between 7 a.m. and 11 a.m., against all other insect intruders except females of their own species. Guarded plants included those visited by females for nectar, or pollen, or both, as well as plants which they were not observed to visit at any time. Newly emerged females make their first flights during the morning hours in search of nectar for their own use. Male territorial behavior increases the probability of immediate mating with these virgin females. Mated females apparently lose their attractiveness to males and are allowed to visit guarded plants without interference. Such females collect pollen between 6 a.m. and 9:30 a.m., primarily from Solanum, and nectar up to about 11:30 a.m., primarily from Asclepias, Verbesina and Larrea. Male belligerence toward other bee visitors to these plants reduces actual or potential competition for pollen and/or nectar, as the case may be. After leaving their territories late in the morning, the males seek nectar for themselves, and later in the afternoon gather gregariously in large “balls” for “sleeping”, in marked contrast to their earlier intolerance of one another.