Bagworms

What are Bagworms?

Bagworms are a highly destructive tree pest commonly found throughout Missouri, especially in urban and suburban landscapes with ornamental evergreens and deciduous trees. These pests aren’t true worms, they’re caterpillars that build and live inside protective silk bags camouflaged with bits of leaves, needles, or bark from the host tree. 

While a few bagworms may go unnoticed, large infestations can quickly defoliate trees, weaken branches, and even kill vulnerable species like juniper and arborvitae. Understanding what bagworms are, how they behave, and how to manage them is key to protecting your trees before serious damage sets in.

What Do Bagworms Looks LIke?

Bagworms are easiest to spot not by the insects themselves, but by the distinctive protective bags they build and carry. These small pests are masters of disguise, and early detection is key to preventing serious damage, especially on evergreen trees.

Here are the most common signs that your trees may have bagworms:

• Silky, spindle-shaped bags hanging from branches or foliage. These bags are made of silk and covered with bits of leaves, bark, and twigs from the host tree. They typically range from 1 to 2 inches long and may resemble pinecones or dead foliage.
  
  
• Clusters of bags found on the outer limbs of evergreens like arborvitae, juniper, cedar, and spruce. If you notice what looks like dried or discolored clumps, inspect closely—they may be active bagworms.
  
  
• Defoliation or browning of needles and leaves, especially on evergreens. Bagworms feed heavily as they grow, and large populations can strip a tree of its foliage, often starting from the top or outer edges.
  
  
• Thin, web-like threads between the bags and branches. These silken attachments keep the bags secured as the caterpillars move and feed.
  
  
• Increased visibility in late summer. As bagworms grow larger and their bags become more noticeable, infestations are easier to detect in July and August.
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• Empty bags from previous seasons. In winter and early spring, you may still see old bags hanging from branches. Each one can contain hundreds of overwintering eggs, which will hatch the following season if not removed.
  
  

How Do Bagworms Spread to Other Trees

While bagworms aren’t fast movers, their ability to infest new trees is surprisingly efficient. Most of their spread happens quietly and seasonally, and homeowners often don’t notice it until the damage is done. Here’s how they typically move from tree to tree:

• Wind-dispersed larvae
  
  After hatching in late spring or early summer, tiny caterpillars (called “ballooning” larvae) can produce silk threads that catch the wind and carry them to nearby trees. This is the primary way bagworms colonize new hosts—especially when trees are close together.
  
  
• Infested nursery stock or transplanted trees
  
  Bagworms can hitch a ride on newly purchased or transplanted trees and shrubs. If the bags go unnoticed, they can introduce the pest to an entirely new location.
  
  
• Overwintering egg sacs left on trees
  
  Female bagworms lay hundreds of eggs inside their bag in late summer. These bags remain attached to branches over winter and hatch the following spring. If you don’t remove them, trees will be re-infested year after year—and nearby trees are at risk, too.
  
  
• Neighboring infestations
  
  If your neighbor has bagworms and doesn’t treat them, wind-blown larvae can easily end up in your yard. This makes neighborhood-wide awareness important, especially for those with arborvitae, juniper, or spruce trees.
  
  
• Birds and wildlife (rare)
  
  Infrequently, bags may be moved by birds or other animals, though this is not considered a major form of spread.
  
  

Common Trees in Missouri At Risk of Bagworms

Bagworms feed on a wide range of trees, but some are particularly vulnerable due to their foliage structure, recovery ability, or prevalence in Missouri landscaping. Here’s a more detailed look at the most commonly affected trees:

• Arborvitae (Thuja spp.)
  
  Arborvitae are often the hardest hit by bagworms. These evergreens have soft, scale-like foliage that is easy for young larvae to chew through. Because arborvitae cannot regenerate from old wood, even moderate defoliation often leads to permanent brown patches or entire tree loss. Infestations typically start at the top and spread downward.
  
  
• Eastern Redcedar (Juniperus virginiana)
  
  A hardy native tree, but when planted in ornamental groupings or windbreaks, Eastern redcedars are easy targets. Bagworms tend to cluster heavily on these trees, and since redcedars grow densely, infestations can go unnoticed until the tree browns out from the outside in.
  
  
• Spruce (e.g., Picea pungens - Colorado Blue Spruce)
  
  With their stiff needles and slow recovery rate, spruces can suffer long-term cosmetic and structural damage from bagworms. Colorado blue spruce, often used in suburban plantings, is especially vulnerable when planted close to other host trees.
  
  
• Mugo and Scotch Pine (Pinus mugo, Pinus sylvestris)
  
  These pines are not the bagworm’s first choice, but once preferred hosts are defoliated, they’ll readily move in. Since pine needles grow in clusters, feeding damage can thin the foliage dramatically, making the tree appear sickly and sparse.
  
  
• Cypress and False Cypress (Chamaecyparis spp.)
  
  These evergreens are susceptible to both minor and major infestations. Bagworms can cause scattered browning initially, but if left untreated, entire branches may brown out and die.
  
  
• Maple (Acer spp.)
  
  Maples are not primary hosts, but bagworms will feed on them when populations are high. Damage tends to appear as small patches of chewed leaves, usually near the canopy’s edge.
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Sycamore, Oak, Elm, and Boxelder

These deciduous hardwoods can experience sporadic bagworm feeding during outbreak years. While they generally tolerate some leaf loss, repeated defoliation can weaken the tree, making it more vulnerable to disease, drought, or structural issues.

How Do Japanese Beetles Spread to Other Trees

Japanese beetles may seem slow and easy to catch, but their life cycle and behavior make them surprisingly effective at expanding across neighborhoods and landscapes. Here’s how they typically spread from tree to tree and yard to yard:

• Flight
  
  Adult Japanese beetles are strong fliers. Once they emerge, they can travel several miles in search of food or mates—especially if nearby trees and plants are already heavily infested or defoliated. This is the most common way they spread locally.
  
  
• Group Feeding Behavior
  
  Japanese beetles release pheromones that attract others to the same feeding site. When one tree becomes infested, nearby trees often follow as beetles gather in clusters and move outward over time.
  
  
• Egg-Laying in Turfgrass
  
  After mating, females lay eggs in nearby lawns or garden beds. These hatch into grubs, which live in the soil over winter and emerge as beetles the following summer. If untreated, this leads to a recurring annual cycle that naturally expands outward.
  
  
• Movement Through Nursery Stock and Soil
  
  Japanese beetle grubs can accidentally be introduced to new areas via the sale and transport of infested nursery plants, sod, or soil. While this is more of a regional or long-distance spread method, it’s a concern for landscapers and garden centers.
  
  
• Wind Assistance (Rare)
  
  Though not their primary method of travel, wind can occasionally help dislodge or carry beetles short distances—especially during peak activity periods when they’re flying between trees.
  
  

Trees Commonly Affected by Japanese Beetles in Missouri

Bagworms feed on a wide range of trees, but some are particularly vulnerable due to their foliage structure, recovery ability, or prevalence in Missouri landscaping. Here’s a more detailed look at the most commonly affected trees:

• Arborvitae (Thuja spp.)
  
  Arborvitae are often the hardest hit by bagworms. These evergreens have soft, scale-like foliage that is easy for young larvae to chew through. Because arborvitae cannot regenerate from old wood, even moderate defoliation often leads to permanent brown patches or entire tree loss. Infestations typically start at the top and spread downward.
  
  
• Eastern Redcedar (Juniperus virginiana)
  
  A hardy native tree, but when planted in ornamental groupings or windbreaks, Eastern redcedars are easy targets. Bagworms tend to cluster heavily on these trees, and since redcedars grow densely, infestations can go unnoticed until the tree browns out from the outside in.
  
  
• Spruce (e.g., Picea pungens - Colorado Blue Spruce)
  
  With their stiff needles and slow recovery rate, spruces can suffer long-term cosmetic and structural damage from bagworms. Colorado blue spruce, often used in suburban plantings, is especially vulnerable when planted close to other host trees.
  
  
• Mugo and Scotch Pine (Pinus mugo, Pinus sylvestris)
  
  These pines are not the bagworm’s first choice, but once preferred hosts are defoliated, they’ll readily move in. Since pine needles grow in clusters, feeding damage can thin the foliage dramatically, making the tree appear sickly and sparse.
  
  
• Cypress and False Cypress (Chamaecyparis spp.)
  
  These evergreens are susceptible to both minor and major infestations. Bagworms can cause scattered browning initially, but if left untreated, entire branches may brown out and die.
  
  
• Maple (Acer spp.)
  
  Maples are not primary hosts, but bagworms will feed on them when populations are high. Damage tends to appear as small patches of chewed leaves, usually near the canopy’s edge.
  ‍
• Sycamore, Oak, Elm, and Boxelder
  
  These deciduous hardwoods can experience sporadic bagworm feeding during outbreak years. While they generally tolerate some leaf loss, repeated defoliation can weaken the tree, making it more vulnerable to disease, drought, or structural issues.