Jul 22

Bagworms: Identification, Damage, and Control

Bagworms are a common pest that can cause significant damage to trees and shrubs if left unchecked. Understanding how to identify, prevent, and control bagworm infestations is crucial for maintaining the health and beauty of your landscape. In this blog post, we’ll explore everything you need to know about bagworms and how to protect your trees from these destructive pests.

bagworm on arborvitae — Bagworm cocoon on Arborvitae

What Are Bagworms?

Bagworms (Thyridopteryx ephemeraeformis) are caterpillars that create protective cases or "bags" from silk and plant material. These bags are often mistaken for pinecones or other natural debris, making them difficult to spot. Bagworms primarily infest evergreen trees, such as junipers and arborvitae, but they can also attack a variety of deciduous trees and shrubs.

Identifying Bagworms

Appearance

Eggs: Bagworm eggs are laid inside the female's bag and can be difficult to see.
Larvae: When the eggs hatch, tiny caterpillars emerge and begin feeding. As they grow, they construct larger bags around themselves.
Pupae: The caterpillars eventually pupate within their bags.
Adults: Male bagworms are moths with black, hairy bodies and clear wings. Female bagworms are wingless, worm-like, and remain in their bags.

Signs of Infestation

bagworms on blue spruce — Heavy Bagworm infestation on Blue Spruce

Bags on Trees: The most obvious sign of a bagworm infestation is the presence of their bags hanging from branches. These bags can vary in size but typically reach 1.5 to 2 inches in length.
Defoliation: Bagworms feed on the foliage of trees, causing noticeable defoliation. Evergreen trees, in particular, can suffer significant damage, leading to browning and needle drop.
Thin Canopy: Over time, heavy infestations can result in a thin canopy, stunted growth, and even tree death if not addressed.

Damage Caused by Bagworms

Bagworms can cause severe damage to trees and shrubs, especially if infestations are left unmanaged. The larvae feed voraciously on the leaves and needles, leading to:

bagworm defoliation on arborvitae — Defoliation on Arborvitae in first year of infestation

Defoliation: Heavy feeding can strip a tree of its foliage, weakening it and making it more susceptible to other pests and diseases.
Branch Dieback: Prolonged infestations can lead to branch dieback, affecting the overall health and appearance of the tree.

Tree Mortality: In severe cases, bagworm infestations can kill entire trees, particularly young or stressed specimens.

Preventing and Controlling Bagworms

Cultural Practices

Regular Inspections: Regularly inspect your trees, especially evergreens, for signs of bagworms. Early detection is key to preventing severe infestations.
Manual Removal: Handpick and destroy bagworm bags during the fall, winter, and early spring before the eggs hatch. This is an effective method for small infestations.

Chemical Control

Insecticides: Insecticides can be effective when applied at the right time. NWI

bagworm feeding on blue spruce — Bagworm emerging from her bag to feed on Blue Spruce needles. Source: Purdue University

ArborCare uses targeted applications that control the target pest without affecting beneficial insects.
Timing: The best time to apply insecticides is when the larvae are young and actively feeding, typically in late spring to early summer.

Biological Control

Natural Predators: Encourage natural predators, such as birds and beneficial insects, which can help reduce bagworm populations.

Conclusion

Bagworms can pose a serious threat to the health and beauty of your trees, but with early detection and proper management, you can prevent significant damage. Regular inspections, manual removal, and timely applications of insecticides are essential strategies for controlling bagworms. If you suspect a bagworm infestation or need assistance with tree care, contact NWI ArborCare. Our team of certified arborists is here to help you maintain a healthy, thriving landscape.