Q. Where do the pantry pests in my kitchen come from? Are they already in the food that I buy from the supermarket? If so, that’s disgusting!

A. Yes, it’s possible to bring home food packages that are already infested with insects or their eggs. Insects end up inside a food package in one of three ways: (1) the package has a broken seal that allows the insect to get into the package, (2) the insect chews its way into the package, or (3) the insects were already in the package when it left the manufacturer’s. This third option is less likely since the manufacturing process usually destroys any insects that are present in the food material. Products can become infested after manufacture, however, if they are improperly sealed (and occasionally even when they are properly sealed), or if the package is damaged.

After the product is packaged, it can still be infested by insects during transportation to the store, or while it is on store shelves, or even from insects already in your own kitchen. It usually takes some time for eggs to hatch or for insects to be noticeable in the package so tracking the infestation back to the source is tricky.

The stored product insects that infest food packages are of two main types, penetrators and invaders. Penetrators are robust insects with strong jaws that have the ability to chew openings into sealed packages. They need an edge to get started, so the more edges or folds on a food package, the more susceptible it is to infestation. Typical penetrators are the rice weevil, lesser grain borer, and the rice moth. Invaders are those stored product insects that usually do not enter packages unless there’s an existing opening. Typical invaders are the sawtoothed grain beetle, flour beetles, and the Indian Meal moth.

You usually can’t tell whether or not a package is infested until you open it. (Although I did see some packages of cat treats on the shelf of my local grocery that were so heavily infested with Indianmeal moths that you could see the webbing and larval feces even on the outside of the box!) The only types of manufactured food packages that are exempt from insect infestation are canned or bottled goods. All other packages are susceptible. The most susceptible packages are paper or cellophane bags.

When shopping, avoid any food package that looks damaged: dented, smashed corners, cellophane seal torn, unglued flaps, torn stitching, etc., or that has tiny holes in the surface. Often boxes that have been nicked by a box cutter will look perfectly normal at first glance. And always check the “sell by” date because older products are more likely to be infested.