There are supposedly (according to code) 4 bees in a beebox. However, double that number seems to spawn when beeboxes are disturbed while the bees are already out. Same thing happens for the beehives as well. At the beginning of the same game I attacked bees from a hive, and found myself surrounded by 12 bees.
So, here is a screenshot of my total 2 bee boxes with 9 bees on screen (there are bees more off screen, I've counted 5 more):
1- Build bee boxes. 2- Time passes. 3- Wait for bees 4 to be out, 4- Collect honey. Expected: No mor bees in the box. Actual: 3-4 more spawn and attack.