I happened to notice these wasps flying around the tops of two chains that hold up a swing on my mother’s covered porch. At first I thought I’d disturbed a nest and made everyone mad. Then the more I thought about it, the more I decided I’d bothered some males that were jockeying for sleeping positions on the chain. Sure enough, I returned close to 9 p.m. (dark) and they were snoozing. Here’s a paper I found on the behavior, which I’d only seen in male solitary bees that sleep together upside down. https://www.researchgate.net/publication/313159553_NOCTURNAL_CLUSTERING_OF_THE_SOLITARY_WASP_CHALYBION_CALIFORNICUM_SAUSSURE_HYMENOPTERA_SPHECIDAE