Hi, thank you all for your input. After moving into the house for 3 wks, I see many beetles around the house. They looks like Japanese beetles according to those online images. I also hear cicadas from the trees in the neighborhood. Besides that, some landscaping guys also guess that it could also be ants who made those holes. And I do see ants in my lawn, big and small. So the conclusion is: grubs damaged the lawn, cicadas and ants made holes on it. And I got to take action on all three of them. I spreaded "Trazicide insect killer for lawn", and I think I see less beetles on my windows at night. But the ants are still happy and active in the lawn. I tried all kinds of ant bait - No Use. And to prevent grubs, i am thinking about GrubEX in the late summer. Any other better options and good experience to share? Thanks!