KC Gardens

Be on the watch for bagworms

Bagworm larvae and bag

Tip of the Week

It is one of the most easily identified insects found in the area, the bagworm. Bagworms are hatching and getting ready to munch their way through many landscape plants. Bagworms form a silken bag mixed with plant parts up to 2 inches in length.

Bagworms will feed on many different plant materials, but their favorite tends to be junipers, spruce and arborvitae. The young worm-like insects eat the foliage, resulting in an initial browning of the area followed by death of the plant, under severe feeding. Understanding the bagworms’ life cycle is important for control.

Bagworms spend most of their lives attached to a branch or stem, eating, never leaving the comfort of the spun bag. Only the males leave the bags to mate with the female, then they die. The female lays eggs for next year’s hatch.

Bagworms over-winter in the egg stage in bags attached to the plant. The eggs hatch in late May through mid-June. At first, the hatchlings are very small. They start out about the size of a sharpened pencil lead. They grow quickly, spinning a larger bag until mid to late summer. The bag is thick, about 2 to 3 inches in length. At that point the bagworms mate, eggs are laid and the whole process is ready to start over for next year.

Bagworm populations build up to damaging levels very quickly, as each bag of eggs can produce more than one thousand hungry little worms. Control of bagworms is best done just after they hatch in the late spring or very early summer. Just about any insecticide will kill the worms while they are small and the silken bag not highly formed. The larger the bag becomes the less effective the control. By late summer, chemical applications are worthless. At this stage, handpicking and destruction of the bags is recommended. This is a slow task that most people would prefer not to do.

There are a number of insecticides that are effective on bagworms at this time of year. Products include bifenthrin, carbaryl or Sevin, Spinosad, Cyfluthrin or Malathion. An organic product called Bacillus thuringiensis is also effective.

Now is a good time to give your evergreen plants a close inspection for bagworms. The populations have been building the last of couple of years. Even though they may seem to appear almost overnight, they can do a lot of damage in a short time.


  1. 10 months ago

    I noticed damage at the very top of an Emerald Green arborvite a few day ago and didn’t waste any time getting out the spray. I had hand picked the whole tree and couldn’t reach the top, so I was expecting to see their handiwork up there.

  2. 9 months, 4 weeks ago

    Great job of monitoring the plants. If all gardeners would do a walk through on a regular basis this insect would be so easy to control. I love it when people call when they are full size then say they just appeared yesterday. Dennis

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