Communal roosting occurs when several insects of the same or different species, gather in close proximity to rest for several hours. These roosts may be by day or by night, in some cases they may be seasonal and may involve more than one species.
Communal roosting has been observed in butterflies, moths, dragonflies, bees, and wasps. Two wasp species and a blue-banded bee species (Amegilla) are profiled in the images here.
This blue banded bee species was observed to attach itself, jaws first to a twig before it settled down on it for the roost.
It is thought that roost sites are selected by specific cues such as smell and visual cues or may involve a generic selection depending upon the species. however, most species exhibit a fidelity for a particular site and will return to that spot daily to roost.
However, damage to the roost site or the presence of predators can result in the abandoning of that site in favour of a better one.
Typically, the insects gather near the roosting site up to 2 hrs before the roost and slowly settle in asynchronously, often involving a lot of jostling and resettling. However, departure from the roost is more synchronous.
Roosting times are dependent on external factors such as overcast conditions, dropping temperatures, and precipitation and can vary settling and departure times by hours.
It is thought that communal roosting may afford these insects protection from predators through increased vigilance, through a dilution effect or even an increased camouflage effect. Besides this other factors such as information exchange, social functions, thermoregulation etc may be involved. No single explanation has so far been able to explain communal roosting for all species of insects.