If you have arborvitae, juniper, or other evergreens in your landscape, bagworm is something worth keeping on your radar. In the Chicago suburbs, we’re seeing this pest more frequently than in years past and when it shows up, it can do serious damage if it goes unnoticed.
As arborists, we often get called in after the browning starts. By that point, the issue has usually been building for a while.
What Are Bagworms?
Bagworms are small caterpillars that protect themselves by building a spindle-shaped “bag” made of silk and pieces of the plant they’re feeding on. These bags blend in extremely well, often looking like small cones or dried bits of foliage hanging from branches. Because of that camouflage, many homeowners don’t realize they have a problem until their evergreens start thinning or turning brown.
Why They’re a Problem for Your Landscape
Bagworms feed on a wide range of plants. In our area, they most commonly affect:
- Arborvitae
- Juniper
- Spruce and pine
They’re not limited to evergreens. We also regularly see them on:
- Honeylocust
- Bald cypress
- Occasionally maples, oaks, and other deciduous trees
While deciduous trees can better tolerate feeding, repeated infestations can still cause stress and thinning over time.
Evergreens remain the biggest concern because, unlike deciduous trees, they don’t replace lost foliage. Once that tissue is gone, it does not come back.
When to Watch for Them
Timing is everything with bagworms. In northern Illinois:
- Eggs typically hatch in late-May through mid-June
- Young larvae begin feeding right away
- They grow and continue feeding through the summer
Each bag you see later in the season may contain hundreds of eggs for the following year, so populations can increase quickly if left untreated.
How They Spread (and Why They Show Up Where They Do)
Bagworms don’t move far as adults and females never fly. So how do they end up all over the suburbs? The key is their early life stage.
Shortly after hatching, tiny larvae disperse by a process called “ballooning.” They produce a fine silk thread and are carried by the wind to new plants. This allows them to move from tree to tree, and even property to property.
Because of this, we often see higher concentrations:
- Along roadways and highways, where wind currents and passing traffic help move them
- In newer developments, where plant material may already carry eggs
- In dense plantings, like arborvitae privacy screens, where they can easily spread plant-to-plant
Those fine silk threads can catch on vehicles, equipment, and nursery stock. It’s not uncommon for bagworms to “hitch a ride” and establish in new areas that way. Once they arrive, they tend to stay. Populations build year after year unless something interrupts the cycle.
Signs You May Have Bagworms
Early on, they’re easy to miss. Keep an eye out for:
- Small, irregular browning on evergreen tips
- Thinning foliage, especially near the top of the plant
- Small hanging “bags” that look like plant debris
If you’re noticing visible bags that are an inch or more in length, the infestation has likely been active for some time.
Why We’re Seeing More of Them
There are a few reasons bagworms have become more common in the Chicago suburbs:
- Milder winters helping them survive
- Heavy use of arborvitae in privacy plantings
- Populations build year after year if not addressed
What You Can Do
- Hand-pick in fall, winter, or early spring
If you can reach them, removing and discarding bags before late-May is one of the most effective ways to prevent problems. - Treat early in the season
When larvae are young (late-May into June), treatments are most effective. Waiting too long makes control much more difficult. - Keep an eye on repeat problem areas
If you’ve had bagworms before, there’s a good chance they’ll show up again without intervention.
When to Call a Professional
If your trees are large, difficult to access, or already showing noticeable decline, it’s a good idea to bring in an ISA Certified arborist. Proper timing and coverage make a big difference, and in many cases, early intervention can save plants that would otherwise continue to deteriorate.
Bagworms don’t usually show up overnight, but they do build quietly. A quick check of your landscape each spring, especially evergreens and commonly affected deciduous trees, can go a long way in protecting your investment. If something looks off, it’s worth a closer look. Catching them early is the difference between a simple fix and losing valuable plant material.
