Bombus sonorus Say (Hymenoptera: Apidae) forages for nectar and pollen at a wide variety of flowers of desert plants (Milliron, 1973; Hurd and Linsley, 1975) and, as most bumble bees around the world, is catholic in its floral choices. Although bumble bees may use nutritional sources other than flowers, for example by puddling at damp patches of soil, presumably for minerals in solution in the same manner as butterflies (Roubik, 1989: 41‐ 43) and for syrup at humming bird feeders (PGK, pers. obs. from the alpine zone of Colorado, alt. 11,500 feet), we are unaware of records of frugivory. The closest recorded similar behavior is that of Bombus spp. feeding at acorn [Quercus rubra L. (Fagaceae)] galls caused by Callirhytis quercusoperator (as C. operator) (Osten Sacken) (Cynipidae) in southern Ontario (Larson, 1999). A few records have been made of honey bees (Apis spp.) foraging at fruit (Flint, 1880; Saxena, 1970; Shaw, 1993; Sihag, 1983; MacKenzie, unpubl., Sheffield, unpubl.) and at oak-twig galls, probably caused by bacterial infections on Q. gambelii Nutt. in Colorado (Kevan et al.,1983). Between 23 and 27 July 1995 we observed large numbers of workers of B. sonorus around an organ pipe cactus [Stenocereus thurberi (Engelm. (Buxb.) (Cactaceae)] at the Arizona Desert Museum, near Tucson, Arizona. Closer inspection revealed that the bees were entering the split fruits and feeding there on the sweet, red pulp. We made observations daily from 23 to 26 July from morning to evening. The bees actively visited the fruits at all daylight hours from 08:00 to 18:00. To check if bumble bees were foraging at night, observations of fruit were made on July 24 and 25 at about 20:00 and 22:00. No bees were seen at these times. At least 5 fruits were being visited on the large plant (ca. 3 m tall with multiple stems), and some bees were seen flying between fruits. The activity within the fruits was intense so that the whole cavity, ca. 4 cm in diameter, was a mass of bees and up to 11 could be counted at one time in a single fruit. As the bees came and went from a given fruit, they landed and took off directly from the split edge of the fruit or from the cactus stem itself. In the latter case, the bees crawled haltingly over the spines before or after flight. No bees carried seeds nor did any have corbicular loads. We did not attempt to mark individual bees to quantify trip times, duration of foraging within the fruits, nor diel periodicity of activity. The period of observation was one of record breaking high temperatures and a paucity of floral rewards in the area. Perhaps circumstances were such that the bees were stressed by those conditions, although water was available in the grounds of the Desert Museum. We also noted other insect frugivors at the fruits, e.g., Coleoptera (Curculionidae) and Polistes sp. (Hymenoptera: Vespidae). Perhaps the presence of stinging insects in the fruits could have interfered with seed dispersal by birds, but it would not have affected dispersal by nocturnal animals. Although our remarks are somewhat anecdotal, we venture them for their general interest in the natural history of bumble bees, cacti, and desert ecology.