Wood boring insect
We have in Minnesota a variety of wood-eating insects. Some are not serious pests - they chew out of the wood and leave and don't reinfest. But some, like the powderpost beetle, can cause damage and can reinfest. Unfortunately, it is difficult to tell what you have based on a photograph of the larva. Here are some websites to help you identify. Look for adults.
If you have powderpost beetles, my recommendation would be to call a professional exterminator.