Acorn Weevils

It’s another mast year for red oak (Quercus rubra) in my neck of the woods, which means that for the past couple of weeks, large nuts have been raining down from the treetops, making it a little treacherous to go for a walk in the forest. Last November, once the acorns had all fallen, Julia and I collected a few gallons of them to process and use for food. (We’ve made tasty acorn bread and acorn cake, but so far our favorite is acorn falafel.)

Anyone who has collected acorns is familiar with the whitish grubs that turn the insides to dust, eventually exiting through round holes like this one:

The grubs are immature weevils in the genus Curculio (Curculionidae).

After collecting our acorns, we dried them by placing them on trays by the wood stove, and I think this arrested the development of most of the larvae that were feeding inside them. However, on December 7 I noticed two mature larvae squirming around on one of the trays.

Just for the heck of it, I dropped both larvae into a jar of soil, and after they burrowed down I put them in the little refrigerator in the basement where all my other bugs pass the winter. I took the jar out on March 1 along with everything else, but it wasn’t until June 14 that an adult finally appeared.

When I was satisfied with the photos I’d taken of it indoors, I brought it out to a red oak sapling in the yard to try for some more natural shots.

It soon wandered onto a young stem, and as I continued to photograph it I realized that it was feeding by chewing a tiny hole into the stem.

In the last photo above, it has finished feeding and the hole is visible just to the left of the tip of its proboscis.

Added 10/25/16: Here’s a great video Laura and David Hughes got last year of a larva chewing its way out of an acorn. Amazing to see it squeeze its blobby body through a hole that is just barely big enough to fit its head capsule.