Sleeping Death

Wandering around the other night with a group from the Museum of Victoria, we came across this phenomenon. This group of halictid bees are sleeping as a unit. This is not too surprising as males of many non-hive, solitary bee species spend the nights sleeping together in clusters on leaves or twigs. To facilitate this behaviour, they usually return to the same site night after night. During the day they cruise around looking for virgin females with which to mate. Some males have well defined territories but still return to the same place to sleep. Bees are not the only insects that sleep in aggregations. We know of many unrelated insects such as bugs, beetles and even some flies with similar habits.

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.