Despite their name, dusk bats (and the Thessian species after which they were named) have little in common with Terran bats, being more akin to mammalian-derived birds. Northern hemisphere dusk bats are smaller then their southern counterparts, rarely more than eight centimetres in length and wingspan, and live in colonies of several thousand. While dormant the bats rest in hibernation hives, subterranean structures much like termite mounds constructed beneath a shallow layer of topsoil. They are herbivorous, and outside their hives avoid the attentions of carnivore predators by detection and evasion.
Dusk bats have a keen awareness of the location and behaviour of their colony-mates, and have been observed maintaining formation and altering direction with one another over distances up to three kilometres, with a precision and instantaneousness that cannot be attributed to their visual or auditory senses. The bats' retiring nature, and instances of poor health resulting from capture for study, has made research into this ability difficult.
Southern varieties of the species are larger, and possess a far more rudimentary version of the location sense. Neither species is presently capable of crossing the higher temperature equatorial zone to reach the opposite pole; their common ancestor is thought to have migrated during an era of more temperate climates.
Though they generally avoid larger life forms, dusk bats are known for a peculiar behaviour dubbed 'dancing', where for ten or twelve nights in a row an entire colony will take to the air en masse and perform intricately coordinated aerial manoeuvres, moving over the course of each night through a course extending large distances from their habitat, including venturing into the airspace above populated areas. Fortunately the bats location ability has been seen to be capable of detecting the emissions of skycar air traffic guides, and consequently they steer well clear of traffic lanes.
A popular theory is based on the belief that the animals' location sense is based on extreme sensitivity to magnetic fields, and an ability to create very specific low-intensity fields themselves. The 'dancing' manoeuvres are thought to be a form of self-calibration, carried out to maintain the precision with which members of a colony remain aware of one another.