I’ve been receiving questions regarding when to spray for bagworms. Bagworms overwinter as eggs in these up to 2″ bags which are formed throughout the summer with silk and evergreen needles by larvae. Larvae feed until late August or early September. Males then emerge and mate with females through the bag opening in September. 500-1000 eggs are deposited by female moths within their own bags.  After depositing eggs, the females drop to the soil and die.  Bagworms overwinter as eggs within bags fastened to twigs such as these shown in this photo.

Eggs hatch in mid-May to early June. Some caterpillar larvae remain on the same trees containing the bags from which they hatched.  Others are blown by the wind to area trees allowing for new infestations to occur.  This photo shows new bags (1/8-1/4″) being formed on trees as they create these bags around themselves.  Look closely for these tiny bags on trees right now.  The video below shows how to look for bagworms on evergreen trees right now.  Study your trees and look for small movements on small bags being formed.  If you are seeing this, consider treating your trees for bagworms.  Products containing bifenthrin or permethrin irritate caterpillar larvae causing them to come out of the bags and be exposed to the pesticide.  There are a number of other management options available.  Please see the following publication for more information.