05 January 2011


Excerpts from a nice post at Naturespeak:
Bagworm sacs are spindle-shaped bags constructed of silk and plastered with dead spruce needles (although they are known to eat just about any plant – over 100 food plants – they prefer evergreens). Each structure is secured to the branch with a silken tie and, depending on whether they were made by a male or female worm, are either empty or full of eggs...

Eventually they emerge as adults in the early fall. The males, wasp-like creatures with clear wings, push their way out of the bag and fly off to seek the company of the females. The females, however, are wingless and are forced to remain within the confines of their bag. When the males find the females they mate with them through the narrow opening at the small end...

The impregnated females lay their egg clusters within the bag before crawling out and dropping helplessly to the ground. She will lay upwards of 1,000 eggs. Both sexes die shortly after mating (although the males are able to visit with a few more bags before cashing it in!) All this means that by wintertime only the female bags will contain living material in the form of yellowish egg clusters. The male shelters will be completely empty or contain the empty pupal skins...
I have seen these on our pine trees and just viewed them as decorated/camouflaged pupae; never knew the interesting backstory. You learn something every day.


  1. Do these things kill the tree or is the tree already on its way out and they take advantage? We had hundreds of these on our spruce and it died shortly afterward.

  2. These seem to be quite common here in Indiana. And to answer Lolamouse's question: yes they can be harmful to coniferous trees and shrubs.

    Here is a photo of the adult male.

  3. I hadn't seen these until NC - interesting that I missed them while in WI. I now live on a golf course and have seen them kill stands of evergreens - I pull them off my Leland cypresses. Bastids!


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