Why there are no infinite number of flies in a room?

Question

Imagine a room on a sunny day, and flies (insects) in that room. You kill all the flies. Next day, new flies are back. Why there are that many flies in the room, not more or less?If there was a constant inflow of flies into the room, after some time you would have an infinite number of flies. I never heard of this happening!One could argue that there is a constant number of flies per volume outside the room and when you kill all the files in the room, there is a negative gradient of flies and the insects will "naturally" move to the room. But such a "fly pressure" would require the flies to bounce from each other, like atoms, which does not seem to happen.Or maybe flies are territorial animals?

superchroma · Accepted Answer

There is also a constant outflow of insects from the room which is less than the influx but not 0, there is a limited supply of flies outdoors to see and then also make it inside the room. Flies are not, however, a constant pressure, their numbers correlate to food sources in the area, as well as cyclic trends which will influence their numbers (predator behavior, etc.).Regarding territory, sort of: "In urban areas, where people live in close proximity and there is garbage, flies have small territories and may only fly 1,000 meters or so. Rural house flies roam far in search of manure, covering up to 7 miles over time." Via: https://www.thoughtco.com/fascinating-facts-about-house-flie...

Someone · Answer

> If there was a constant inflow of flies into the room, after some time you would have an infinite number of flies.
With a constant finite inflow, you’d only have infinitely many after infinite time.
As to why they don’t keep amassing: flies need food, water (moisture), warmth and oxygen. Stuff too many in a room, and conditions elsewhere will be better for them.

bediger4000 · Answer

Flies have senses like vision, that mean they don't have to bounce off each other like gas molecules do.

Rackedup · Answer

If you leave your windows open with no screen, they come in and go out... You would probably end up seeing about as many flies as you see outside, unless you have some rotting meat in your kitchen or something similar.