The larva of carpet beetles (often called "woolly bears" or "buffalo moths") can damage carpet, furniture, and clothes. They are also frequently found in stored powdered foods and grains (where they are often incorrectly called weevils) and are significant in that they will get into insect collections and destroy the collected specimens.
 For previous invasions (one in our old apartment and one in my research lab), see here and here.
Pyrethroids are synthetic chemicals based on the chemical structure of pyrethrin I (left) and pyrethrin II (right), insecticidal compounds produced by the chrysanthemum species Chrysanthemum cinerariaefolium and Chrysanthemum coccineum.
Chemical Structure of Pyrethrin I is by Benjah-bmm27, available at http://commons.wikimedia.org/wiki/File:Pyrethrin-I-2D-skeletal.png.
Chemical Structure of Pyrethrin II is by Benjah-bmm27, available at http://commons.wikimedia.org/wiki/File:Pyrethrin-II-2D-skeletal.png.