The small, pale worms you find inside chestnuts are almost always the larvae of chestnut weevils, a group of beetles that lay their eggs directly into developing nuts while they’re still on the tree. Finding one is startling but extremely common, especially in wild-harvested or untreated chestnuts. The larvae aren’t toxic, and with the right post-harvest treatment, you can prevent them from ruining your haul.
What the Worms Actually Are
Chestnut weevils are small, brown beetles with a distinctive long snout. Two species are responsible for most infestations: the lesser chestnut weevil and the greater chestnut weevil. The adults use that elongated snout to bore a tiny hole through the shell of a developing chestnut, then deposit eggs inside. When the eggs hatch, the creamy white, legless larvae feed on the nut’s flesh, growing to roughly the size of a grain of rice before chewing an exit hole and dropping to the ground.
The larvae you’re seeing aren’t actually worms at all. They’re grub-like beetle larvae, plump and C-shaped, with a small brown head. If you crack open an infested nut, you’ll often find one or two larvae along with dark, powdery waste (called frass) mixed in with damaged nut meat. The exit hole they leave behind is a clean, round pinprick in the shell, which is one of the easiest ways to spot an infested nut from the outside.
How Chestnuts Get Infested
The entire process starts in late summer, while the nuts are still forming inside their spiny burrs on the tree. Adult weevils emerge from the soil, where they may have been living as pupae for one to three years, and climb the tree to feed and mate. The female drills into the soft shell of the immature nut and lays a few eggs inside. By the time the nut ripens and falls in autumn, the larvae have been feeding inside for weeks.
Once the chestnut hits the ground, the mature larvae chew their way out and burrow into the soil, sometimes several inches deep. There they pupate and wait, sometimes for multiple years, before emerging as adults to start the cycle again. This long soil stage is one reason weevil populations are so persistent in areas where chestnuts grow. Even if you skip a harvest year, the weevils are still underground, waiting.
How to Spot Infested Nuts
The simplest screening method is a water float test. Drop your chestnuts into a bucket of cool water and wait a minute or two. Nuts that float are likely infested, dried out, or otherwise compromised. Healthy, dense chestnuts sink. The float test isn’t perfect, since a nut can have a small larva inside and still be heavy enough to sink, but it catches most of the worst cases and is worth doing with every batch.
Beyond the float test, look for these signs:
- Small round holes in the shell, about the diameter of a pencil lead. This means a larva has already exited.
- Dark or soft spots on the shell surface, which can indicate decay following insect damage.
- Lightweight feel when you pick up the nut. A healthy chestnut feels solid and heavy for its size.
- Powdery brown debris inside when you cut the nut open, a sign that larvae have been feeding.
Are They Safe to Eat?
The larvae themselves are not toxic. In many chestnut-growing cultures around the world, finding a worm in a chestnut is treated as a minor inconvenience, not a health hazard. If you accidentally eat one, it won’t make you sick. That said, infested nuts taste off. The larvae consume starch and leave waste behind, which gives the nut a bitter, unpleasant flavor and a mealy texture. Most people discard any nut that shows signs of feeding damage simply because it doesn’t taste good.
If you cut into a chestnut and find a small tunnel or a patch of discolored flesh but no larva (it may have already exited), you can trim away the damaged portion. If the remaining nut meat looks clean, firm, and pale yellow to cream-colored, it’s fine to use.
Post-Harvest Treatments That Work
If you’re gathering chestnuts in any quantity, treating them right after harvest kills any larvae inside before they can cause more damage or crawl out onto your kitchen counter. Two approaches are well established.
Hot Water Treatment
A hot water dip is the most effective and widely recommended method. Research from UC Davis outlines three temperature and time combinations that kill larvae reliably:
- 122°F (50°C) for 30 minutes
- 131°F (55°C) for 15 minutes
- 140°F (60°C) for 5 minutes
After the dip, dry the chestnuts thoroughly before storing them. Residual moisture promotes mold, which is a bigger storage problem than the weevils themselves. Spread the nuts in a single layer and let them air-dry for a day or two. This treatment also helps sanitize the shell surface, reducing the chance of fungal issues during storage.
Freezing
Holding chestnuts at 0°F (-18°C) for four days also kills larvae. This is the easier method if you have freezer space. The trade-off is that freezing can alter the texture and flavor of the nut somewhat. If you plan to roast the chestnuts right away, you may not notice much difference. For longer storage or if flavor matters to you, the hot water method is the better choice.
Preventing Infestation for Growers
If you have your own chestnut trees, the most effective non-chemical strategy is prompt, thorough harvesting. Collect nuts as soon as they fall, ideally every day or two during peak drop. The faster you get nuts off the ground, the less time larvae have to exit and burrow into the soil to continue the cycle. Removing and destroying any nuts left on the ground after harvest reduces the local weevil population over time.
Keeping the ground beneath trees clean and free of leaf litter also helps, since it makes the soil less hospitable for burrowing larvae. Some growers lay tarps or ground cloth under trees during harvest season to make collection faster and more complete. Because the weevil pupae can survive underground for multiple years, population control is a long game. Consistent sanitation year after year gradually reduces infestation rates, but a single neglected season can set you back.
Store-Bought vs. Wild Chestnuts
Commercially sold chestnuts have typically been treated with a hot water dip or fumigation before reaching the store, so finding a live worm in a grocery store chestnut is uncommon. It does happen occasionally, but the rates are far lower than what you’d encounter foraging or harvesting from backyard trees. If you buy chestnuts from a farmers’ market or a small local grower, ask whether they’ve been treated post-harvest. If not, run them through the hot water or freezer treatment yourself before storing them. Either way, doing a quick float test takes two minutes and saves you from biting into an unpleasant surprise.