Acorn and Nut Weevils
The adult acorn weevil is a brown beetle about 3/8 inches in length, and has a very long, thin snout. The larvae is a legless grub which is curved and fat in the middle, tapering toward both ends. The larva is creamy white colored with a brown head, and can grow to be 1/4 to 3/8 inches long.
Adult females lay their eggs inside developing nuts on the trees during mid summer. The egg hatches into a creamy white, grub-like larva that feeds inside the nut until fall. When the acorns fall to the ground in autumn, the larva chews a perfectly round 1/8 inch hole in the nut and emerges in late fall or early winter. The larvae then tunnel into the soil, where they will stay for one to two years before emerging as a new adult weevil to repeat the process.
The larvae can eat out the entire nut inside an acorn or hickory nut, making it worthless, but they usually do not damage the tree in any way. The reason you often find so many "wormy" or "holey" nuts under the trees is because the squirrels leave them behind. It appears squirrels can select good nuts during their fall frenzy of gathering. If you want to collect the good nuts for yourself, you will have to get up early and beat the squirrels to it.
Control of nut weevils in backyard oak and hickory trees is not practical. Nut growers use insecticides similar to the apple growers to prevent egg-laying by the female weevils. This is prohibitively costly for the private home owner.
For more information please see this article: The dark side of collecting acorns.