There are a few insects that really bug Nebraskans, but one of those are bagworms. Bagworms are a major pest of coniferous or evergreen trees from June to August. These destructive caterpillars are called bagworms because they feed, grow, and live all, or most of their lives inside a bag. They remain mobile though because their head and thoracic legs stick out as they feed all over the host plant. When they are disturbed they can retract and cinch up the bag, which is already highly camouflaged.
Bagworms are a pest of juniper, pine, spruce, arborvitae and other evergreen species. They will also feed on deciduous trees like shade, ornamental, and fruit trees, but because deciduous plants drop their leaves and grow new ones each year, the defoliation does not often kill the tree. Evergreen trees though, do not shed their needles and large populations of bagworms can kill the tree.
Hundreds of tiny bagworm caterpillars in Nebraska emerge from their bag(s) in late May/early June. (The first ones ones I saw were in Omaha May 25, 2019). They begin feeding and promptly find protection by covering themselves with a protective bag made from silk and their host plant material. They feed and grow, as as they do, their bags become enlarged. Mature caterpillars stop eating in August and attach the bag a branch with a strong strand of silk and pupate inside. Male bagworms pupate and emerge as moths in the fall. Females bagworms transform into a wingless moth, but do not leave the bag. Males moths locate the female bags, mate with the females, and then die shortly thereafter. After the female lays 200-300 eggs inside her bag, she dies, and the eggs overwinter. The eggs are heavily insulated inside the pupal case inside the silk bag. There is one generation per year.
Dealing with bagworms can be extremely frustrating because:
- Bagworms remain incognito until major damage is detected.
- Newly emerged bagworms can disperse with the wind from nearby trees.
- Bagworms are difficult to control in large trees (like windbreaks) because they are cannot be reached to physically remove or treat with insecticides.
- Bagworms remain protected in the bag and there is a small window for effective insecticide treatment (after caterpillars hatch, but before bags are 1/2-inch long).
- Bagworms are not picky about their host plant and will feed on all types of plants.
Management for bagworms include:
- Cutting or handpicking the bags off and destroying them before caterpillars emerge late May.
- Destroy bagworms by dropping them in a bucket of soapy water or seal them in an airtight bag that they cannot escape.
- Bacillius thuringiensis (kurstaki) is a biological insecticide that can be applied to foliage to kill young caterpillars as they feed.
- Must have complete coverage
- Must be consumed to be effective
- Works best in June when bagworms are small
For our bagworm infographic.
Watch the bagworm segment from Backyard Farmer