Next time you’re at Mount Pisgah, take a moment to pick up a few acorns from the ground. Chances are, you’ll be able to find one with a pinhead-small, circular hole in the shell. That’s likely evidence of an acorn weevil, and it was all I’d ever seen of one until recently.
I have to thank fellow Mount Pisgah volunteer Bryan Ribelin for letting me know he’d spotted this spectacular nut weevil in the Curculio genus. The timing was right for the females to be scouting green acorns that were not too soft, not too hard, in which to bore holes and lay eggs.
These charming beetles use their comically-long rostrums to tunnel near the cap, and deep inside new acorns. The sharp, nut-piercing parts are at the tip of the snout, and the rostrum’s prodigious length allows them to excavate a deep nursery for their offspring, out of danger from many predators.
After making the hole, the weevil turns around and deposits an egg or two. The resulting larvae eat the acorn meat, safe inside their shell, until it falls off the tree. In the fall, and after the literal fall, the larva chews its way out, making a different hole, the round ones you’ll see in the abandoned nuts. It’ll spend a year or two worming its way through the soil before it pupates and becomes an adult, ready to climb up an oak tree to look for acorns.
I highly recommend watching the video linked below. It shows a female acorn weevil drilling into a nut. You’ll see her maneuvering around in circles, her rostrum diving ever deeper into the acorn, and her round head rotating like a ball joint as she goes. In the overhead shot from Mount Pisgah, you can see how the antennae fold up into grooves on the rostrum, so they don’t get in the way as she bores.
Weevils are generally small insects, but this one, at about three-eighths of an inch long is a mid- to large-size model. Keep in mind, those white oak acorns are pretty big.
Stay curious!
See more of Karen’s work here.
Sources:
Sources:
Must-see footage of acorn weevils at work, from KQED’s Deep Look: https://www.youtube.com/watch?v=rVYlWiFKXEg. Accessed 8/18/25.
Charley Eisman on rearing an acorn weevil, which includes a video of a larva chewing its way out of an acorn: https://bugtracks.wordpress.com/2016/10/24/acorn-weevils/. Accessed 8/18/25.
All photos by Karen Richards.