Year for bagworms?

When I get one call about an unusual pest I typically tally it as an interesting day.  When I get two calls, I begin to wonder.  When I get three calls about the same pest issue it’s an infestation.  Today I got my third call about bagworms on roses–this one from Janet Laminack in Denton County.  My other calls were from Rockwall and Smith counties.

Damage and bagworm-like insects on rose.  Image courtesy Dr. Keith Hansen, Smith County.

Damage and bagworm-like insects on rose. Image courtesy Dr. Keith Hansen, Smith County.

Although bagworms can feed on a variety of different plants, 128 by one count, they generally prefer arborvitae and bald cypress in my part of Texas.  The most common species of bagworm (there are 20 species in North America), and one of just a few known bagworm pests, is the evergreen bagworm, Thyridopteryx ephemeraeformis.

Bagworms have one of the more interesting life cycles from a pest management point of view.  The female bagworm, it turns out, is wingless.  The males emerge from their bags of silk and leaves and cast about for a good-smelling female; but alas, the female is doomed to stay at home in the bag all her days.  All this means that bagworms have to be quite ingenious if they are going to disperse to new plants or sites of infestation.

Basically there are just a few ways for bagworms to get around.

Closeup of the silken bag carried by bagworms, festooned with leaves from its host plant.  Image courtesy Dr. Keith Hansen.

Closeup of the silken bag carried by bagworms, festooned with leaves from its host plant. Image courtesy Dr. Keith Hansen.

  1. crawl, which for a one-inch insect carrying a protective bag around, is not very efficient;
  2. be blown on the wind when still very small–much more efficient, but one would have to have perfect weather conditions occurring at the same time as the very small bagworm caterpillars were hatching and dispersing; or
  3. be spread by people–the ultimate road trip for insects.

The bottom line is that bagworms don’t usually move very fast, or very far.  So why would we be seeing an uptick in bagworm numbers this year… on plants that they normally are not so common on?  The answer is not clear to me, but ideal weather conditions this spring for wind dispersal is my best guess.  This, coupled with good conditions for egg hatch and larval survival, could make this a good year for bagworms.

What to do with those bagworms?  If you see these insects on your plants, there are several good control options.  Bacillus thuringiensis is an old standby, especially for smaller caterpillars.  Spinosad is another good low-impact insecticide.  After that, or for larger caterpillars, I recommend going to one of the pyrethroid insecticides.  I list these last because, even though they are relatively safe for people, they can be a little hard on beneficial insects.

Damage by bagworms to Italian Cypress.  Notice the reluctance of the caterpillars to move even a few feet to a different tree.  Damage by bagworms to evergreen trees can be severe.  Image courtesy Geoff Sherman, North Richland Hills Parks and Recreation.

Damage by bagworms to Italian Cypress. Notice the reluctance of the caterpillars to move even a few feet to a different tree. Damage by bagworms to evergreen trees can be severe. Image courtesy Geoff Sherman, North Richland Hills Parks and Recreation.

If you fail to control bagworms now, or they never seem to get bad enough to treat, be sure that you inspect your roses and other plants closely this winter when they have few leaves.  Bagworms are one of the few pests that can be effectively removed by hand.  Because bagworms generally overwinter in the egg stage (except possibly in south Texas), every bag you remove in the winter holds the potential for hatching 500 to 1,000 eggs the next spring.

If you’ve observed unusual bagworm numbers this year, I’d like to know.  Leave a comment in the box below to share your observations.

4 Responses to Year for bagworms?

  1. Linda Hawkins says:

    I planted three Italian cypress on the north side of my house in Keller seven years ago. I have noticed a few bagworms in earlier years but this years is unbelievable. In previous years appoximate total of bagworms per tree: 10. This year just a 6in x 6in area of a Cypress: At least 10 small bagworms. Imagine 3 trees, 2 stories high. That is a lot of bagworms. I normally use very little pesticides. I have not taken any steps to get rid of the bagworms because I just noticed this on June 12, 2010. (2 days ago). If I do use a pesticide Neem, Bt, Spinosid are the pesticides I prefer depending on the situation. I have never sprayed for bagworms before but I am afraid that this amount of infestation will kill my trees if I don’t.

  2. I have a number of evergreen shrubs. They are just covered up in bag worms. I have sat many hours trying to pick them off. I’ll never get them all. I went to Home Depot and bought insecticide with the Bayer brand. It said it is for shrubs and trees. It says to spray it every 30 days. I am still picking off the worms, which are not dead after their spraying. If I keep spraying them every few days will it finally kill them?
    Thank you.

  3. Sandra says:

    OMG!! We have them all over our leyland cyprus. We have approximately 21 leyland cyprus trees. We began to see the top of one of the trees showed distress with yellowing brown branches. We checked the ground for possible over watering or dryness. We asked our landscaper to check the trees out. Lo and behold they remove a branch and see these things hanging over them that resemble pine cones made off the trees needles. What was eerie was that they dangled and began to move. (so creepy, they give me the heebie jeepies) Since then we visited our local nursery & they recommended that we treat them with a natural product (can’t remember name) which paralysis the worms jaw and can no longer eat. We did spray them but the infestation is so severe that we have chosen to pick them off. Unfortunately, it’s so time consuming & they are cleverly hidden. We have been picking off buckets & buckets of these suckers. We first burned them. Lately, we are drowning them in buckets filled with water, soap & bleach. (disgusting). We’ve probably picked over 2 or 3 hundred..could be in the thousands. We’ve been at it a couple of hours a day for over two weeks. We recently noticed that the bald cyprus trees on the median down the street look dead and are loaded with these hanging bagworms. This is bad!!! By the way we live on Inwood Road near Lovers Lane in Dallas, Texas.

  4. Jennifer Harvey says:

    We are in East Parker County. We seem to have bag/web worms on several of our trees and shrubs this year – I even found a few in the Canas! I am researching the best way to get rid of them, but I’d love some suggestions. Thanks!

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>