Asked August 14, 2014, 2:32 PM EDT
New Castle County Delaware
You may have a pest known as bagworm building cocoons in your foliage. These insects commonly feed in arborvitae and you will see their case of clippings develop in May and June. See Greg Hoover's fact sheet here to determine if this is your pest.
http://ento.psu.edu/extension/factsheets/bagworm Your pest life cycle may be two weeks to a month ahead of ours here in Pennsylvania, due to quicker spring warming.
To verify your pest, you may want to visit the Delaware Cooperative Extension office near you. You can be more assured of an accurate finding than my remote efforts.