I love the concept of this game. There are some cases when the jar won't move after getting stuck on the head of the flies. There are also some rare instances that the head of the fly is inside the jar but still not considered as captured. There are also some cases when the red beetle is captured when the jar's lid is not capturing the beetle on this position: 
This usually occurs when the jar is stuck between two insects. Maybe consider adjusting the colliders if you are using that :)
But overall, nice game. Good luck with it