Dampness can cause brass parts to develop verdegris, especially when it is in contact with felt or leather, both of which attract and absorb moisture. The steel connecting rod shown here has rusted from exposure to dampness. Note the rust under the felt-covered tip. Moths Moth larvae are actually the culprits. They eat felt, as on the pallet valve shown here.
Moths like to lay their eggs in an accessible cranny such as a reed cell.
Note the nest in this reed cell. This causes a problem when the egg cases lodge in the reed so that the reed cannot sound. Moth larvae can also work their way to the underside of the soundboard to eat the felt underneath the pallet leather. This pallet valve has suffered such damage. This undermines the leather and causes a cypher, or leak, which makes the note sound even when the corresponding key is not pressed down.