What did the trap catch?

The count in a trap becomes useful only once you know what is in it, because different findings point at completely different problems. A carpet beetle in a textile store is an emergency. A spider beetle in the same trap is a housekeeping note. A silverfish is a message about humidity.

Fabric pests

These are the group that does the most damage to collections, because they eat keratin: wool, silk, fur, feather, hair, horn and skin.

Webbing clothes moth. Small, pale golden, and reluctant to fly, tending to run rather than take off when disturbed. The damage is done by larvae, which produce silk webbing and tubes on the material and leave grazed patches and holes. The presence of webbing and frass is the reliable sign; the adults are simply the visible part.

Case-bearing clothes moth. Similar in scale, distinguished by the larva carrying a portable case constructed from the material it has been eating, which is often the first thing found.

Varied carpet beetle and other Anthrenus species. Small, rounded, mottled adults that are often found at windows because they fly to light and feed on pollen outdoors. The larvae, known as woolly bears, are bristly, elongated and shed distinctive cast skins. Those cast skins are frequently the first evidence, and they persist long after the larva has gone, so a single skin is not proof of a current problem.

A rising fabric pest count is the finding that justifies immediate action: isolate the affected material, inspect thoroughly, and plan treatment.

Wood borers

Common furniture beetle. The familiar small round flight holes in furniture, panelling and structural timber. The larvae live inside the wood for years, so the holes are a record of past activity, not a live count. Distinguishing active from historic infestation depends on the appearance of the holes and of any bore dust: fresh holes are pale-edged with clean, gritty dust beneath.

Wood borers usually indicate damp, because most species need a moisture content in the timber that dry indoor conditions do not provide. A live infestation in a store is a humidity finding as much as a pest one.

Damp-associated feeders

Silverfish. Tapered, wingless, fast, and strongly associated with humid conditions. They graze starch, size and surface coatings on paper, book bindings and wallpaper, leaving irregular grazed areas rather than clean holes.

Booklice. Very small, pale, often found in numbers where humidity has been high. They feed largely on microscopic mould rather than on the paper itself, which makes them a direct signal of a damp problem.

For both, the useful response begins with a data logger rather than a treatment. If the space dries, the population declines on its own.

Scavengers

Spider beetles and similar species feed on organic debris, dead insects, and accumulated material in voids and under furniture. They are rarely a direct threat to collections. A rising count is a housekeeping finding, and it also indicates there is enough debris in the building to sustain other populations.

Reading damage rather than catches

Some evidence never reaches a trap.

Frass, meaning insect droppings and bore dust, accumulates below active feeding and is often the first thing noticed. Its texture and location indicate the group. Webbing and silk tubes point to clothes moths. Cast larval skins point to carpet beetles. Grazed surfaces without holes suggest silverfish. Clean-edged round holes in wood suggest borers.

When an inspection finds any of these, the material should be isolated in sealed bags immediately, before it is carried through the building, and the traps in that area checked at a shorter interval until the picture is clear.