I live near a forest with a canal, and often see fruit flies, they also sometimes come in our house and occasionally feed on bits of fruit. Also, sometimes I meet regular house flies here and there, and also in the city I commute to.
I noticed that most fruit flies and alike most often fly in circular shaped trajectories in the air, their curvature of flight contains bends, as if they were riding an invisible rollercoaster all the time. Their flight can be faster or slower, centered around a lamp fixture or near my face eventually, but most importantly, circa 80% of the time I see them flying in this fashion. Also, this is the way I see regular flies flying around, in 99% of cases.
On the other hand, in roughly 20% of cases when I see fruit flies flying, they fly in straight lines, with abrupt and sharp changes in their direction. This is usually (but not necessarily) slower than their rollercoaster way of flying, and it can also be varied regarding how often they change direction abruptly. However, this "sharp" way of flying is extremely rare in case of the house fly, I have only seen it two times actually, so let's say it happens in 1% of house flies.
What are these distinct flying styles? What is their cause? Are both styles natural and should occur in healthy fruit flies, and house flies as well? Then why is it much rarer in case of house flies? Isn't the "sharp" style a result of some infection around these animals? Those house flies that I saw flying in the "sharp" pattern were rather slow anyway, and I saw them in/near my home. Does it occur more rarely in cities?
Thank you for any helping answers, I am very curious!