Silverfish

• WHAT YOU SEE

A quick, silvery, fish-shaped insect that darts for cover the second you turn on the bathroom light. Sometimes it's in a closet, on a stack of old magazines or a cardboard box that's been sitting a while. They don't bite and they don't fly, they just move fast and low, which is usually all anyone remembers about them.

• WHAT WE SEE

Silverfish eat starch: the glue in a book binding, wallpaper paste, the sizing in fabric and cardboard. Finding them consistently in one spot, a closet, a bathroom, a bookshelf, points at a humidity problem before it points at a bug problem, since silverfish need damp air to survive. Bathrooms without good ventilation and basements that run humid are the two places we find them most in Chicago and St. Louis homes. A few silverfish rarely mean structural damage; a lot of them, especially near stored paper, is worth a closer look.

• HOW WE FIX IT

We treat the cracks and voids where silverfish are hiding, in the bathroom, the closet, or wherever the stored paper is, as part of a quarterly visit. Cutting the humidity does more long term than any treatment: a bathroom fan that's actually used, a dehumidifier in a damp basement, boxes stored off a concrete floor. We'll say so if the fix is really about moisture rather than more product. Free re-service applies here the same as anywhere else if they turn back up before the next visit.

• WHEN THEY SHOW UP

Silverfish don't disappear for winter the way outdoor insects do, since they're living entirely indoors and following humidity rather than temperature. They're most noticeable in summer, when Midwest humidity is highest and bathrooms and basements run damp longer. A silverfish in a bedroom closet usually means the closet is holding moisture it shouldn't; one in the basement is a much more common story. Both rooms are where we look first.

• WHAT THE PROS KNOW

Silverfish eat starch: book glue, wallpaper paste, the sizing in fabric. Finding them means a humidity problem before it means a bug problem.