I’m pretty fascinated with acorn weevils these days, since I’m seeing a lot of them while processing my acorns. I finally looked them up, and it turns out they have a fascinating life cycle.
There are two types of acorn weevils (beetles), long snouted and short snouted, Curculio and Conotrachelus, respectively. They both plant their eggs in acorns, but the short snouted one seems to do this in cracked acorns once they are on the ground. The long snouted variety is the one that you’re going to run into acorn processing, because unless you’re drinking your bathwater for breakfast, you’re not going to be picking up cracked acorns.
The female weevil, whose snout is as long as her body (about 3/8″), digs a hole in a green, developing acorn with tiny appendenges on the end of her snout. She sucks the oily nutritious juice out of the acorn, and thus fortified, lays her eggs in the hole, and plugs the hole with her own poo. The grubs hatch in the continuous buffet which is the acorn, and snuggled up in there, snacking, until the acorn falls from the tree. By this time (as Nature is smart) they are ready to leave the acorn, and they take the fall to the ground (which must be quite a shock) as a signal to start chewing their way out of the acorn. How fast this happens depends on how thick the acorn’s shell is — anywhere from a few hours to three days.
The grubs always chew a perfectly round, 1/8″ hole. It’s just big enough for their head, and they have to squeeze and wiggle their fat, shiny acorn-stuffed body through the hole to escape. Once they fall to the forest floor, they hurry to bury themselves in the soil before something comes along and eats them. If they make it, they take a multiyear nap underground (I’ve read anywhere from 1-5 years). They don’t eat, but they somehow metamorphose into their adult beetle form. When they wake one fine summer day, they crawl out of the soil, mate soon after, and start the process all over again.
There’s some points to be taken here for the forager. The first is that just because there’s no hole in the acorn doesn’t mean that there’s not a grub in it. A hole means a grub has already emerged. It may have siblings which will also be emerging soon. Or not. Or if the acorn has been on the ground for a while, another insect may have moved in. No hole means nothing.
However, if you’re collecting fresh acorns, you’re going to know that you’ve got about a 3 day window in which you may see larvae emerge from your stash, leaving their distinctive holes behind. (You may even see individual acorns in your stash wiggling, like giant jumping beans!) This is not a problem, just something to know, for the sake of storage, or squeamish loved ones.
The acorn they emerge from may or may not be useable. You can open it and check it out–or opt not to. It will be likely to be at least 50% spoiled, in any case. It may also have more fresh grubs in it, trying to make their way out. You may well chop them in half with your knife, and feel oddly bad about the whole thing.