How do rice weevils get into a sealed bag of rice?

The "sealed" invasion by the rice weevil (Sitophilus oryzae) is a misunderstood process.

Rice weevils do not chew through sealed packaging to enter a bag of rice — although their mandibles can chew through grain husks, they are not strong enough to chew through thick, sealed plastic bags (unless it is a very thin, single-layer plastic film).

The real reasons rice weevils appear in "sealed" rice bags are several: ① The most likely reason — the eggs were already laid inside the rice grains before you purchased it.

The female rice weevil uses her mandibles to chew a tiny hole (virtually invisible to the naked eye) on the surface of a rice grain, lays a single egg inside, and then seals the hole with a secretion.

This egg hatches inside the grain, the larva develops inside, pupates, and the adult emerges by chewing its way out from the inside — by the time you find adult weevils in your "sealed" bag of rice, their entire life cycle (from egg to adult, about 4–6 weeks at 25 °C) has been completed inside the bag.

② The packaging has a tiny tear or incomplete seal — even a pinhole-sized opening is enough for adults to enter or exit.

③ After you opened the packaging — adult weevils flew or crawled in from outside and laid eggs in the incompletely sealed storage container.

Prevention method: Place newly purchased rice and flour in the freezer at -18 °C for 48 hours — this can kill any eggs that may be present in the rice grains — then transfer to airtight glass jars for room-temperature storage.

Relying solely on the original packaging's "seal" is insufficient — the original package may have already contained eggs when it left the factory.