Bagworms

 

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...