They've been busy munching, mating, and moving around all over your stuff in the deep dark recesses of your closets and drawers. This is the hostess gift they leave behind -- a fancy filigree along the edge of paper sheets or perhaps a lacy version of the former full page.
Nasty little creatures. They feed on paper and glue and look for a nice moist place to play. Cookie crumbs bring them running at full speed. They even like hair and dandruff!
Silverfish can be found anywhere stuff is stashed, especially in damp and humid places. When you see them, bring in the vacuum. Wipe down all surfaces. Air out the cupboards and leave desiccant packets in enclosed spaces. Keep things as clean as possible. And, try not to eat cake in the closet.