Question
I have grubs. Now I find plugs of dirt about half the size of my thumb all over the lawn  I was told that it may be some kind of predator feeding on the grubs.. It's worst than the grubs...  

Answer
The animal that is eating the grubs are most likely moles. Moles feed off grubs and earthworms.

If moles are the problem, you definitely need to rid your lawn of the grubs.  This can be accomplished by using a pesticide called Grubex or by applying a bacterial spore to your lawn called Milky Spore.  Milky spore is more expensive, but the bacteria that kills the grubs multiplies every year over a period of 15 years, therefore only needing to be applied once. Although the bacterium is fatal to grubs, it will not harm beneficial insects.  Once their food supply is gone, moles will normally relocate to another location.

In the short term, you can either place poisoned pellets in their entrance holes, or kill it by trapping.  Be sure to use a trap specifically designed for moles.  These can be purchased at most garden centers. Place the trap above the tunnel in the center of the runway, normally between two holes.  If you do not catch it within two days, move it in one foot increments.  This trap is especially designed to "snap" below the surface. It can take several days, so be patient.

Good luck, and please write again if I can ever provide assistance.

Regards,

Mike