mealworm

The larval stage of the mealworm beetle (Tenebrio molitor), a species of darkling beetle.

We buy mealworms to supplement our chickens' feed ration, and they do some scratching in the yard to find other bugs too.

This or any other larva that looks similar and is found in similar circumstances (i.e., in meal, in flour, in food, in the pantry, in feed, in the feedroom), such as the larva of a mealmoth (flour moth).

Near-synonym: waxworm

They'd seen a few mealmoths and mealworms in recent days, and then they figured out that the cornflakes in the pantry were the source of the problem.