Homalonychus selenopoides Marx 1891 is endemic to the coastal plains of the Sonoran Desert in the state of Sonora, Mexico and the southwestern United States. Although the species was described more than a century ago, nothing is known about its behavior. We collected spiders in the southern Sonoran Desert to study their reproductive behavior, which we recorded with an infrared camera, mainly at night. Sperm induction was of an indirect type; males wove a triangular sperm web about 2 cm² near the ground. Females and males prepared threads of silk and sand. Courtship behavior was intermediate between levels I and II, and the copulation position was a modification of type III, where the male tied the female's legs with silk before mating. Sexual cannibalism may occur during mating. Females began to spin their egg sac at ∼11 days after mating and completed it in ∼15 h, including ovipositioning. The outer layer of the egg sac contained sand, and the sac was surrounded by a garniture of cords of silk and sand, possibly to protect the eggs from desiccation and as a barrier to parasites and predators.