Overspawning of mobs

animals (including squids in water) and hostile mobs are rapidly spawning everywhere around my area (im in a plains biome) and that cause a lag on my phone and increase the memory of my world. I have to cheat and /kill @e to kill all the animals in my survival world. This happens start from 1.2.0 to 1.2.5 beta, I have a picture of my survival world that spawns a group of mobs, this happens so many time on me but I forgot to screen shot it, please fix this ASAP.