Moths and weevils, step by step
Interactive lesson: grain and flour insects without chemicals — identification, early checks, tidiness and cold, freezing, no oxygen, diatomaceous earth and the larder.
Free sample Chapters 1 and 2 (8 steps) are free. The full lesson comes with the Moths and weevils module. Already bought? Unlock
This lesson is general guidance, not professional training. Local regulations and expert advice always take precedence. Read our disclaimer.
The whole lesson as text
1. Know the enemy
Grain insects fall into two groups: internal and external.
- Internal insects — Weevils, the lesser grain borer and the Angoumois grain moth develop inside whole kernels. You can't see them until they come out; the signs are round holes and hollow kernels.
- External insects — Flour beetles, the Indian meal moth and the Mediterranean flour moth eat broken kernels, germ and flour. The signs are threads, webbing and flour stuck together in lumps.
- Warmth speeds them up — At 25–30 °C (77–86 °F) it takes 4–6 weeks from egg to adult. Infestations surge in May and June, when the store goes above 18–20 °C (64–68 °F).
- Cold slows them down — Below 15 °C (59 °F) weevils and moths barely breed. A cold store is half the defence.
Why: A weevil bores into a kernel, lays an egg and seals the hole, so from the outside you see a healthy kernel. By the time the first beetles come up on top of the drum, the third generation is already inside. Moths show up sooner: threads on top of the grain and little moths in the evening.
- The insect's name matters less than its group: beetles in whole grain mean the whole lot has to be stopped.
- If you're not sure, put a few insects in a small jar with a little alcohol and show them to an extension service.
2. Spot it early
Even 1–2 live insects per kilogram of grain mean it's time to act.
- Sieve a sample — Sieve 1 kg (2 lb) of grain from the top and the middle through a 2 mm sieve onto white paper. You'll see beetles, larvae, dust and broken kernels.
- Float test — Put 100 kernels in a glass of water. If 2–3 float, the infestation has started; if 10 or more float, the lot is heavily infested.
- Hand in the middle — Push your hand, a rod or a thermometer into the middle of the heap. A warm spot is a weevil nest.
- Traps — A probe trap in the grain catches beetles weeks before your eye does. Hang a pheromone trap at eye level, away from windows.
Why: A small infestation is easy to stop, a big one is hard. Looking alone isn't enough, because internal insects can't be seen.
- Pheromone traps don't protect grain, they only show what's there. One is enough for a larder, 2–3 for a granary.
- Go into the larder in the evening with a torch: flying moths show up on the walls and ceiling.
3. Tidiness and cold · Locked
Buy the Moths and weevils module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.
4. Freezing · Locked
Buy the Moths and weevils module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.
5. No oxygen and diatomaceous earth · Locked
Buy the Moths and weevils module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.
6. Moths in the larder · Locked
Buy the Moths and weevils module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.