We had a moderate harvest of acorns this year. Some years you can’t step outside without crunching a foot full, but this year it was a hunt to find whole nuts. The squirrels have been busy too, and they leave the grub infested acorns and take the sound ones. As I’m collecting, I check the nuts for grubs. The acorns with a hole have had at least one grub leave, so the nutmeat inside has already been mostly consumed. If there is no hole, I pop off the cap. If the cap end of the nut is whole and solid, I collect it. If it looks like “dirt” collected at the end, I leave it; there is a grub actively at work consuming the nutmeat.

Adult female acorn weevils bore a hole into the developing acorns when they are still on the tree (TAMU). The grub develops inside, feeding on the acorn. When the acorn falls, the grub bores a hole out of the shell then burrows into the dirt to develop into an adult. I don’t need a reference for the second part. When my eldest was about 4, we made an autumn decoration with play dough and acorns. Later I found a grub happily munching through the dried play dough and a hole in one of the acorn. Did we throw it out? No, of course not. We filled a mason jar half full of dirt, put the grub inside, and capped it with a metal screen (for air flow) so we could see what it developed into. The next Spring, there was an adult acorn weevil, which we released back outside.

If you are collecting acorns for decoration, I’ve heard freezing them will kill the grubs, if you don’t want surprise inhabitants.