One week your arborvitae looks completely normal. The next, half of it is bare and dropping needles like it's already October. Most homeowners blame a storm, or maybe some kind of blight. Here's the thing though — the real culprit is usually hanging right there in the branches, disguised as a little pinecone or a scrap of dead debris. That's a bagworm bag. If you've never noticed one before, don't feel bad. They're built to be overlooked, and that's exactly why a bagworm problem can go unnoticed for an entire season before anyone realizes what's happening.
What A Bagworm Infestation Actually Looks Like
Bagworms are caterpillars — the larvae of the bagworm moth — and their signature move is spinning a spindle-shaped bag out of silk mixed with bits of the very leaves or needles they're eating. So each bag ends up camouflaged in the exact color and texture of its host tree. On an arborvitae, it looks like arborvitae. On a spruce, it looks like spruce. That's why so many people walk right past an infestation without a second glance.
Evergreens take the brunt of it. Arborvitae, juniper, cedar, spruce, and pine are the usual targets, though they'll also feed on a handful of deciduous trees and shrubs when the mood strikes. If you rely on a row of arborvitae as a privacy screen, that's exactly the kind of spot they favor. The bags start out tiny, barely bigger than a grain of rice, then grow to roughly two inches by late summer as the caterpillar inside keeps eating and adding more material.
How They Spread Without Flying
Here's where it gets interesting. The caterpillar never actually leaves its bag — it drags it along every branch it visits, only poking its head and legs out to feed. Disturb it, and the whole thing yanks back inside like a turtle retreating into its shell. So how does an infestation end up in the tree next door?
It's not what you'd expect. Adult males do grow wings and become moths, and they'll fly around looking for mates. But adult females never develop wings at all. They spend their entire lives inside the bag, mate right there, lay a few hundred eggs, and die without ever going anywhere. In short, the females aren't spreading anything — they physically can't.
The actual spread happens earlier, when eggs hatch in late spring. Tiny larvae crawl out, spin a strand of silk, and catch the wind — a dispersal trick known as ballooning. That's how they travel from tree to tree without a single one of them flying. The other common route is far more human: infested nursery plants or trimmed branches getting moved from one property to another, bags and all.
Why They're Worse On Evergreens Than Other Trees
A maple or oak that loses some leaves to them will usually push out new growth and bounce back fine. Conifers don't have that luxury. Needles don't regenerate the way broadleaf foliage does, so a heavy, unnoticed infestation can genuinely defoliate — and eventually kill — an arborvitae or spruce that's been quietly losing ground all season. That's the real risk here: not that they're dangerous, but that they're patient, and by the time the damage is obvious, a lot of it is already done.
We hear about this a lot from clients who are already on a maintenance schedule for something else. If you're getting regular ant control in Montclair, for example, it costs your technician almost nothing extra to glance up at the arborvitae hedge while they're already on the property.
What To Do If You Spot Them
If you catch a light infestation early — just a handful of bags scattered on one or two shrubs — handpicking works surprisingly well. Pull the bags off by hand sometime between fall and early spring, before the eggs inside hatch, and drop them in soapy water or the trash. That alone can knock out a small population before it ever becomes a real problem.
That said, once bags are numerous, spread across a taller tree, or showing up on multiple plants around the yard, it's time to bring in a professional, especially for anything you can't safely reach with a ladder. Either way, don't wait for ballooning season to pass — the earlier the caterpillars are dealt with, the less damage they do. Plenty of homeowners already lining up mosquito treatments in Wayne this time of year simply add a bagworm check to the same visit.
Bagworms are one of those pests that reward a closer look. Take a walk past your evergreens this week, especially if you've noticed thinning or browning that never quite matched up with storm damage. And if you'd like a second set of eyes on the whole yard, not just the bagworms, a full property pest evaluation from our team will catch it along with anything else quietly working against your landscaping.