Beautiful lawn turned ugly

Well, my lawn starts to discolour and dry patches are now so obvious. And last night, I crushed a slimy creature in my garden. The next day, I got up early to check what that was, then I found out that a lot of grubs are infesting my lawn. What causes all these? The discolouration, dry patches, and swarming insects? Are there any practical ways to solve such icky problem? I wish not to resort to harsh chemicals because it can also destroy my lawn.



Thanks for all the future help!