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BAGWORMS

Steven Frank & James R. Baker (Emer.), Extension Entomologists

CAUTION: This information was developed for North Carolina and may not apply to other areas.


Bagworm, Thyridopteryx ephemeraeformis (Haworth), Psychidae, LEPIDOPTERA


General Information

male moth emerged from bag bag on twigBagworms are common landscape pests because they feed on many of the most common ornamental plant species.  They can be readily identified by the cone-shaped bag they spin from silk and embed with bits of host plant and other debris.  The bags range in size from 1/4 inch to over 2 inches to accommodate the growing caterpillar inside.  Though they are rarely seen outside of bags, the caterpillars are 1/8 to almost 2 inches long depending on age. The head and forward parts are dark with a hardened head capsule.  The rest of the body is paler and soft.  In late summer dark brown pupae can be found in the bags. Male pupae are slender and female pupae are fatter.  Adult female bagworms are wingless, legless and grub-like (they never leave the bag). Males are small, brown hairy moths with dark wings that clear with age. In fall the female lays hundreds of spherical or oblong eggs within her pupal cast skin that overwinter and hatch in spring.

Biology

girdled twig from bag

Bagworms occur throughout North Carolina. Bagworms are usually found on conifers such as arborvitae, spruce, juniper, cedar, and Leyland cypress. However, bagworms have a very wide host range and can feed on many plant species including deciduous trees and shrubs. 
Female bagworms lay 500-1000 eggs in their bag before they die in the fall.  The eggs overwinter and hatch in May and June. The newly hatched larvae spin down on silken threads and are blown about by the early spring breezes. Most of the larvae land on the original host plant but some small worms may be "ballooned" for some distance on the silk thread. Upon reaching a suitable host, the worm spins a tiny bag of silk and plant debris that looks like an upside down ice cream cone (figure).   As the caterpillar grows the bag grows also and more host plant material is added to the outside for camouflage. In addition, the larger bags hang down from branches like pine cones rather than sticking straight up.  In August the caterpillars mature and molt into the pupal stage. The bag is firmly attached by a sturdy silk band which the bagworms usually wrap around a twig. During August and September, adult bagworms emerge as moths from the pupal case.  Females are flightless and never leave the bag so male moths emerge from their bags in search of females to mate with.  Mating occurs through the bag. After mating, females lay their eggs inside the pupal cast skins and die. tiny larva dropping down on silken thread

Apparently when the newly hatched larvae reach a plant which is different from its parents' host plant, the insects often have difficulty adapting and may die or may produce only a few offspring. After several years of struggling to keep from going extinct, the population may hit on the right combination of genes for the "new" plant and "suddenly" the new plant is covered with bagworms.

Damage

First stage larvae feed on the leaf surfaces leaving small areas where the epidermis has been removed.  Older larvae consume entire leaves. New bagworm infestations often go unnoticed until late in the summer when caterpillars are large and consuming a lot of plant material and branches begin to appear defoliated.  Trees that do not produce new foliage will not recover and may die.

Monitoring

Monitoring for bagworms is easy when the bags are large and easy to spot on trees and shrubs.  Look for bags in fall or early spring before eggs hatch.  Anytime you see old bags on a plant there are probably bagworms present because the females lay eggs in their bags.  Thus the same trees and shrubs will be damaged year after year as populations build.   

Decision making

Bagworms can cause severe damage to landscape plants by defoliating branches that alter plant shape and habit.  In nursery and retail settings just a few bagworms cause enough damage for consumers to reject a plant.  If bags are present the plant will be unsalable.  Therefore the decision of when and how to control bagworms will depend on the plant location, value, and purpose. 

Intervention/ Control

Bagworms are parasitized by several kinds of parasitic wasps.  A 2005 article by J.A. Ellis et al., reported that bagworm infested arborvitae (Thuja) plants in Illinois, surrounded by a high density of asters such as Shasta daisies, showed high rates of parasitized larvae.  In many cases natural parasitism and predation may keep populations below noticeable damage levels. Because females do not fly, infestations can be concentrated and localized in a landscape. For example only four or five trees in a hedge row of 50 plants may be infested. Scouting can verify this.

Control

A selection of insecticides labeled for use on bagworms on ornamental plants in:Greenhouses (G), Nurseries (N), Landscapes (L), and Interiorscapes (I).

Active ingredient

Trade name

Labeled location

Signal word

IRAC
MOA
group

Compatible with
beneficials

acephate

Orthene

G, N, L

Caution

1B

No

acetamiprid

TriStar

G, N, L

Caution

4A

Yes

*azadirachtin

Azatin

L

Caution

18B

Yes

*Bacillus thuringiensis (B.t.)

Dipel, others

G, N, L

Caution

11B2

Yes

Beauveria bassiana

Naturalis

G, N, L

Caution

M

Yes

bifenthrin

Talstar

G, N, L, I

Caution

3

No

*bifenthrin

Onyx; (some consumer products)

L, I

Caution

3

No

chlorfenapyr

Pylon

G

Caution

13

Yes

chlorantraniliprole

Acelepryn

L, I

none

28

Yes

cyfluthrin

Decathlon

G, N

Caution

3

No

fenpropathrin

Tame

G, N, L, I

Caution

3

No

*spinosad

Conserve

G, N

Caution

5

Yes

tebufenozide

Confirm

N, L

Caution

18A

Yes

* Suitable for homeowner use. (Homeowner formulations of permethrin and cyfluthrin are also available.)

J.A. Ellis et al., "Conservation Biological Control in Urban Landscapes: Manipulating Parasitoids of Bagworm with Flower Forbs", Biological Control 34(1), July 2005, 99-107.

Moore, Robert G. & Hanks, Lawrence M. (2004)
Aerial dispersal and host plant selection by neonate Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae).
Ecological Entomology 29 (3), 327-335.


Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.
© 2001 NC Cooperative Extension Service


ENT/ort-81
Revised by Steven Frank June, 2010.
Web page last reviewed Janary, 2011 by the webperson.