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How to Bag a Bagworm

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Dr. Tom Weissling

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Bagworm closeup
Photo Credit: © 2003 Buglady Consulting
In this close-up of a bagworm, it's easy to understand how the pests can be mistaken for pinecones.
There's one word I'd use to best describe bagworms: "weird!" These are truly odd but fascinating insects that live throughout the eastern US, west to Nebraska and south to Texas. Unfortunately, they're also very damaging to several species of trees, including juniper, arborvitae, cedar, pine, hemlock, spruce and honey locust. Other trees such as cypress, willow, black locust, sycamore, apple, maple, elm, poplar, oak and birch can also be attacked.

Bagworm larvae feed on the foliage of these plants, creating open areas in the canopy. This can even cause tree death if bagworm populations are high enough over a long period of time.

So, why the name "bagworm?" Well, caterpillars that just hatch from their eggs secrete a silken bag around them. While the young larvae feed, bits of plant material are incorporated into the "bag." As the caterpillars grow, their bags enlarge with them. What's really weird about this is that the caterpillars move the bag around with them as they feed, and they can withdraw back into their bags when disturbed, much like a turtle. These bags are spindle-shaped and reach a length of 1 1/2 to 2 inches.

Bagworms survive winter as eggs laid inside their mothers' bags. In May or June, eggs hatch, and the young caterpillars crawl from these bags and start to feed. They continue to feed and grow throughout summer. In late summer, typically August, the caterpillars attach their bags firmly to the tree on which they're feeding and enter the pupal stage, where they change to adults in early fall.

Facts
  • Bagworms often go unnoticed for a long time because people often think the bags are pinecones or some other plant part.
Tips
  • If insecticides aren't for you, try using a vigorous water stream to blast the little caterpillars off the leaves.
 
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