I took a class entitled "Pantry Pests" years ago. The good news is, those little weevils are actually high in protein and edible (that was just too icky to think about). In fact, that's how 3rd world vegetarians get their B12, according to the instructor.

If you happen to store pet food or bird seed in your pantry, they are often the main culprit for bringing pantry pests into the house because the standards for storage are different from food. Although the little buggers can be in almost any box and bag of food when you bring it into the house. Be sure to store pet food in an air-tight container and away from your food storage.

Regular cleaning. Make sure you vacuum those gaps between shelves and the wall. Don't provide pests a "buffet" with some spilled flour, cornmeal, etc., or bits clinging to the outside of storage containers. Proper air-tight storage is the key (canisters, jars and glass canning jars with screw-top lids or vacuum-sealed lids). Eliminate paper bags, plastic bags, and boxes when you bring them into your home. Pests will chew through plastic bags containing grains/seeds/beans to get to the contents. You can cut the cooking instructions from the package and tape it to the container. Slip it into a fold-lock plastic sandwich bag and vacuum-seal it with the contents. OR, make a file with the collapsed box or only the instructions clipped from the box.

If you have your home sprayed for "bugs" on a regular basis, that will also help. You may also want to have an exterminator in after such a large infestation.

I store hundreds of pounds of grains/seeds/beans and have never had an infestation (knock on wood), but I use oxygen-free storage.

You can avoid infestation by storing dry goods in vacuum-sealed storage. Vacuum-sealing with a FoodSaver and/or adding oxygen absorbers will eliminate the oxygen, which will kill any pest present and will eliminate the eggs/larva from surviving.

Bay leaves is also often suggested, but the science to support that seems to be at odds. Some say it deters, but doesn't kill. From Utah State University - Food Storage in the Home: "Bay leaves, chewing gum are not effective. The only instances where they have been effective are when no insects were initially present in the food." Another scientific source: "The addition of bay leaves, chewing gum (mint flavored or otherwise), 10-penny nails, or salt will not prevent contamination of grain by insects." My class instructor (an entomologists) said bay leaves don't work - but I guess they can't hurt.

Freezing is another method that kills weevils, if you happen to have enough freezer space to park dry goods there for a period of time when you bring them home. But there is also some questions about how long in the freezer, and whether it will kill eggs.
-Grainlady

The hardware store sells little tents called "Pantry pest traps." They work AFTER you clean up a major infestation. Anything else that comes in the pantry with larvae will gravitate to the bait trap and die. Prevents major infestations.
I also freeze flour for two weeks before transferring to air tight containers in the cupboard. I keep cereal and beans in the frige in the garage til needed.