Recently I was reading late at night and a large fly was buzzing around. The pitch of the buzz varied slowly making perhaps 2 or 3 discernible pitches per second. I was reading by a single light whose switch was near at hand. The fly was slightly annoying and on impulse I turned off the light. The buzz pitch immediately stopped changing and a constant pitch buzz continued for about 2 seconds whereupon there was a slightly satisfying splat.

This suggested to me that the fly had no stored model of its environment with which to continue navigating. Sight bore on its flight plan un mediated by memory. A person walking thru a room will not immediately stumble if the lights go out. The person holds a model of perhaps 2 to 5 meters ahead and can employ that model in responding to the unexpected situation.

Neither the human nor the fly has evolved in an environment where the lights go out suddenly and unexpectedly. The human’s reserve information is presumably related to Hawkins prediction model which posits a world model presumably for planning such mundane things as where to put your foot. My observation of the fly suggests only shorter range plans; perhaps nothing we would call a plan. Movies of a fly landing on a ceiling reveal at least a complex reflex action, but perhaps not a plan.

This is all consistent with a plausible proposal that insects have a primary navigation technique of flying so that the angle between the Sun and heading is constant. I don’t have a reference. Together with a rule that the angle between heading and down is some constant near 90º seems like a sufficient short term flight plan. Downness is problematic for both flies and autopilots. I doubt that flies have gyros as good as those of autopilots. The fly may need short term orientation memory since likely orientation senses are likely to be sporadic. I suspect that turning rate is easily sensed by eye and this can provide short term orientation memory if there is light and no fog. Pilots and perhaps flies get disoriented when flying in fog where visual sense of even turning rate vanishes. Long term orientation sense is likely gravity as it effects air velocity for autopilots and most flying bugs.