Crawlies with Cri: Acorn Weevil (Curculio glandium)

Acorn Weevil (Curculio glandium) Photo by Christy

My, what a big nose you have! Meet the acorn weevil (Curculio glandium).
Let’s get a couple “need to know” facts out of the way – while acorn weevil larvae do kill the single acorn they feed on, management of these weevils is not practical, and most acorns will survive. Acorn weevils don’t cause any damage to the trees themselves.
Unless you are planning on gathering acorns for sale as seeds, there’s no reason to have any concerns about acorn weevils whatsoever. If you want to gather acorns for crafts, wait until after the first couple of freezes and you’ll get “bug free” acorns. Let’s learn why.
Backing up a bit, the acorn weevil is in the Genus Curculio: “Nut and Acorn Weevils.” There are approximately 30 species of nut and acorn weevils in North America. Each species specializes in a different type of nut, but they lead similar lives.
Adult acorn weevils emerge in early to mid-summer. Theyware tiny beetles, only one-quarter to three-eighths of an inch long. Their impressive snouts can be as long, or even longer, than their body length.
Around mid-summer, the females use these nifty schnozzles to drill into developing acorns. It’s not just the size and shape of their snouts that enable them to do this; their mandibles (chewing mouthparts) are on the tip of their snout.
Once they’ve drilled through the husk of the acorn, they’ll lay a single egg inside. The larvae will hatch and eat all the nut meat, growing to their full pre-adult size. Then they wait for fall when their acorn nursery drops to the ground, and they’ll crawl out and dig into the ground to mature for two more years before emerging as an adult.
It’s a pretty risky system all around. Not only do the larvae have to survive the fall, but their acorn has to land on or near soil. It’s tough luck for those whose acorns land in a creek or river as so many do.
They also have to survive band-tailed pigeons who will sit up in oak trees swallowing acorns whole all day long.
Luckily for the weevils, squirrels are more discerning. They don’t want the nuts with the larvae and will leave them on the ground when gathering their winter stores.
If you want to gather acorns for craft projects, you’ll have to beat the squirrels to the larva-less ones. Or, if, as mentioned above, you wait until after the first good freeze to gather nuts for craft projects, the larvae will have abandoned them already.
The “escape holes” drilled by the larvae are easy to see, and of course nuts that have had the meat eaten weigh less than those that are whole.
So, don’t “go nuts” with worry over having nut weevils in your acorns. Appreciate these funky little critters for their highly specialized niche and “against the odds” lifecycle.