Exodus 23:28-30

I will send the hornet before you, which will drive out the Hivites, the Canaanites and the Hittites, from before you. I will not drive them out from before you in a single year. Otherwise the land would become desolate, and the animals of the field will multiply against you. But little by little I will drive them out from before you, until you are fruitful. Then you will possess the land.