In this case, site fidelity works against the bees. Minute fungal spores greet the bees as they return to sleep and thus they become infected. The amount of time it takes for the infection to grow and kill the bee is unknown but the infected bee may fly around while the fungus grows within his body. Eventually, the bee takes his final sleep and does not awake The developing spores of the fungus can be seen as they await to “dust” newcomers to the night roost.
Like soldiers in a line, this group of sleeping male halictid bees seems normal enough. But most are doomed.
This group on an adjacent leaf never awoke one morning. They have been killed by a parasitic fungus. Two of the bees on the right are readying themselves to assume their "death pose" as the fungus can be seen on their antennae.
The fungal spores are clearly seen in this individual bee. The spores can be air borne and infect others as they return to the site night after night. Or bees can be infected simply by coming into contact with the spores that are on the leaves themselves.