Herein are described the nests and their contents of Xeromelissa nortina (Toro and Moldenke) and of X. sielfeldi (Toro and Moldenke), found in the dry, high Atacama Desert of northern Chile. Nests of the former, discovered in 2014, contained linear cell series in the central pith channels of dead, broken twigs of Baccharis, revealing clear, cellophanelike cell linings that presumably control cell humidity. From the cells, postdefecating larvae were obtained, permitting their description and comparison with our meager understanding of other larval xeromelissines. Nests of X. sielfeldi, also found in broken dead twigs, were discovered and first studied in 1971 before the species was described and named, thereby delaying publication until now. Although similar in most respects to nests of X. nortina, they occupied abandoned beetle burrows. Toro and Moldenke provided information on eggs, predefecating larvae, and pupae, described herein. At the time of that discovery, adults of X. rozeni (Toro and Moldenke), a bee with an exceedingly long proboscis, were also active, permitting observation on their feeding habits, which are included herein.