Bagworms Tie One On.

Published on

As summer draws to an end, many insects and mites approach the end of their seasonal activities as well.  Curtis Young reports that the majority of common bagworms (Thyridopteryx ephemeraeformis) have finished their destructive feeding as caterpillars in their individual bags, have tied their bags to their host plant, and are pupating (pupa=3rd stage of their life cycle).


Bagworm eating spruce needle
Bagworm eating its last meal before tying off to the host plant in preparation to pupate.


Curtis has observed numerous plants in NW Ohio that have been ravaged by bagworms this summer.  The most severely impacted plants are evergreens such as arborvitae, Colorado blue spruces, and junipers.  However, we also have to remember bagworm can and does survive very well on many other plants that are not evergreens such as honeylocust, maple, oak, and sycamore.  The damage to these non-evergreen plants is less significant to the plant's health, but these populations of bagworm are resources of infestations that can transfer to other plants next year.


Bagworm producing silken band
Bagworm spinning silken band around stem of host plant.


Management of bagworm at this stage of their development is limited to hand-picking of the bags off of the host plants.  Remember, however that the silk that the bagworm spins to attach itself to the host plant is incredibly strong and will take some effort to break it off.  Unfortunately, trying to break the silk is not successful and the host plant tends to break first.  Thus it is advisable to use a small pair of scissors to snip the silk rather than trying to break it.  Bagworms are not limited to tying their bags to plant material.  Curtis and other BYGLers have observed bagworm bags tied to exterior house and building walls, sculptures, outdoor furniture, signs, and headstones in cemeteries.  Bagworms will not be overly susceptible to insecticide sprays again until next year when newly hatched caterpillars reappear in the month of June.


Bagworm parasitoid wasp
The generalist caterpillar parasitoid wasp, Itoplectis conquisitor, searching a bagworm bag to parasitize.  


Other insects that were flying around these bagworm infested host plants were parasitoids (parasitic wasps) searching for bagworms to parasitize.  The largest and most easily seen was a wasp, Itoplectis conquisitor (Family Ichneumonidae).  This wasp is a generalist and will also target several other caterpillars. This makes the wasp a less dependable ally in suppressing bagworm. Fortunately, there are many other parasitoids, as well as predators, that feast upon bagworms. Collectively, they can have a significant impact on reducing bagworm populations.