The nymphs of these bugs are quite intriguing because they cover themselves with debris, dust, bits of fluff, grit, etc. Both adults and nymphs, according to Bug Guide "prey on small arthropods such as woodlice, lacewings, earwigs, bed bugs...", thus a useful insect to have around. To see the nymph: http://www.pbase.com/laroseforest/image/144168593