I did a little home research today. I wanted to see if I could figure out just by looking at an acorn if it had something in it. I had a hunch about the Tortricoidea Moth Caterpillar I found here so I collected a bunch of acorns and my hunch proved to be true. Notice in this pic the acorn has a hole in it but it has been resealed from the inside. The second pic shows the caterpillar after I cracked it open and you can also see the hole sealed from the inside. The third pic shows an acorn with a hole but not sealed. Every acorn I collected that had the sealed hole had one of these caterpillars in it but the ones where the hole wasn't sealed had nothing.