Yup they are weevils as you found out. They are already in the corn (as eggs) when you buy it, then you bring it home and the eggs hatch and those ones lay more eggs and pretty soon you have a ton of those nasty little things. I don't use corn much so when I buy a bag it usually sits in the garage a while. I've had some weevils hatch out a few times when I leave the corn sit for months. Not a big deal but if they get in your house they could feed on any grains/cereal they can find. I never saw them anywhere other than in the corn itself, or on the outside of the bag.