I would check in with your county extension agent (do they have those in California?) or call U. C. Davis to find out more about identification and habits. If the grubs coagulate anywhere in your yard you could douse them with diatomaceous earth (d.e.).
Other wise, I would watch and learn. Are they doing any harm, or are they doing some good, or, are they just minding their own business? There may be some kind of plants that might discourage them, marigolds for example. If they are crop theatening Im sure your local ag college has information.
