Skip to main content

Bagworms can kill your trees – What to know to get rid of them

From sticky scale bugs on the undersides of leaves to spider mites meshed in webbing, many pest infestations are glaringly obvious. But bagworms operate a little more subtly — they spend a lot of time inside brown “bags” or cocoon-like structures that resemble tree wood and pine cones.

Over time, bagworms work insidiously and can inflict potentially fatal damage on trees, so it’s ideal to get rid of them as soon as you notice their presence. Here are the key things to know about bagworms and what to do when you become aware of an infestation.

Bagworm on a branch
Image used with permission by copyright holder

What are bagworms?

Here’s the deal: Bagworms aren’t worms. They’re actually caterpillars that turn into moths. Bagworm larvae can camouflage as pine cones or other tree structures in their bag cocoons that measure around 1/4 to 2 inches. These structures generally look like hanging ornaments and are made up of various plant materials. Spending most of their time inside their bags, bagworms commonly come after landscaping trees and shrubs, such as junipers, spruces, pines, and cedars

Adult maggot-like females can’t fly, but they mate with winged male moths and can lay between 200 and 1,000 eggs per bag. After laying their eggs, the female bagworms fall to the ground and die as the eggs overwinter in their bag sack.

What does bagworm damage look like?

Bagworms generally only feed for six weeks, but they can do a lot of damage in those six weeks, as they hang onto tree twigs and branches with tough silk strands. They can even kill entire trees in a matter of years. The telltale sign of bagworms is the brown cone-like bags they live in.

When it comes to tree damage, you’ll notice brown foliage, dead wood, and disappearing foliage with time. Bagworms can also spread to neighboring landscape plants with a little help from the weather. While pupating, bagworms spin silk threads that can blow via the wind onto nearby trees.

Bagworm caterpillar in grass
Image used with permission by copyright holder

How to get rid of bagworms

Handpicking bagworms

Anytime between winter and late spring is the best time for managing your bagworm problem. The eggs tend to overwinter, hatch in the spring, and start pupating in the summer. The easiest way to manage bagworms is to handpick them during the time frame between winter and spring.

To cut bagworm bags off your plants, use a knife to sever the silk band that bagworms use to wrap around twigs and branches. You can leave the bags out for bagworm predators, such as parasitic insects and birds, but it may be best to destroy or discard the bags yourself.

Avoid letting the bagworm eggs fall to the ground and hatch, as this could get the bagworm cycle going again. You can simply submerge the bagworms in a bucket of soapy water and seal the soaked bagworms off into a plastic bag when you throw them away.

Insecticides 

Best left for heavy bagworm infestations, insecticides can be effective, but they don’t always work and may harm animals, such as cats and fish. The best time to use an insecticide is when the larvae have just hatched and are relatively weak — this is around late spring or early summer.

You can harvest bags in the winter or early spring, then leave them in a jar for observation. When you notice the eggs hatching, you can spray your pesticide onto infested trees. Some of the most effective pesticides for bagworms are ones with pyrethroids as the active ingredient, which paralyzes the caterpillars. You can find these insecticides at your local garden center.

By late summer, the pests will have already mated and laid their eggs, so handpicking is your only option because insecticides will not be as effective on adult bagworms or pupating ones. Fortunately, summertime is when it’s easiest to find bagworms because they’re actively feeding; unfortunately, that also means you may see more cone bags emerge and infestations defoliating your trees.

Bacillus thuringiensis

Bacillus thuringiensis, or Bt, is a type of bacteria that you can use to kill pests by keeping them from feeding. It’s commonly found in local nurseries as a spray and isn’t known to be harmful to humans and pets. Again, late spring or whenever bagworms immediately hatch is the best time to apply Bt because larvae are more sensitive around this stage in their lives. Spray your Bt solution every week until you don’t see any more bagworms.

Raking autumn leaves
Elena Elisseeva / Shutterstock

How to prevent bagworms

The easiest way to prevent bagworms is by checking your saplings when you first bring them into your garden. You also want to check your trees often for any signs of bagworms to catch them before they start reproducing rapidly. Also, clean your garden regularly and rake away and destroy egg sacks if you see them. 

Using predators to your advantage can also be key in preventing bagworms. To attract bagworm-preying birds, such as woodpeckers and sparrows, set up birdbaths or make your trees more habitable for nesting by leaving thickets to naturally form. Other helpful predators are ichneumonid wasps, which you can attract by planting asters next to vulnerable trees. 

Bagworms can evade detection and damage plants in subtle ways, so it’s best to watch out for them in your garden. If you happen to find them taking over your trees and shrubs, fret not. While you can bring in insecticidal sprays or Bt, handpicking them is the easiest way to diminish their population. So be patient and don’t despair — while bagworms work in quiet, menacing ways, it’s a relatively straightforward process to get rid of them. 

Editors' Recommendations

Stacey Nguyen
Stacey's work has appeared on sites such as POPSUGAR, HelloGiggles, Buzzfeed, The Balance, TripSavvy, and more. When she's…
When should you harvest watermelons? What you need to know
Get the timing right for your watermelon harvest
Freshly cut watermelon slices

Knowing when to harvest watermelons can be tricky, especially if you’re used to growing crops like tomatoes, where there’s an obvious physical change (like turning from green to red) that indicates ripeness. Watermelons go through more subtle changes, so they can be difficult to spot if you don't know what to look for. If you're wondering if your watermelons are ready to harvest, this is the guide for you. We'll break down everything you need to know about when to harvest watermelons for the perfect summer snack!

How to tell your watermelons are ready for harvesting
Most watermelon varieties are ready to harvest roughly 1 month after the plant has bloomed, or 2 to 3 months after planting your watermelon seeds. The exact time can vary depending on the type of watermelons you're growing, what the weather has been like, and whether all the plant's needs have been met.

Read more
Does Epsom salt kill ants (and is it safe)? Here’s what we’ve found
Could this inexpensive staple really be the solution to your pesky ant problem?
Hand in a brown and white glove holding a pile of Epsom salt next to an evergreen tree

Ants play a vital role in the ecosystem, but they can also be a major pest for gardeners. While the ants themselves aren't necessarily a problem, they can protect and support more harmful pest species, such as aphids. Ants can also take advantage of damage done by other pests, exacerbating existing problems.

There are many products on the market that promise to kill ants, but some of them are also dangerous for animals, plants, or people. If you’re looking for a safer alternative to get rid of your infestation, you may have heard that Epsom salt will do the trick. Does it actually work, though, and are there any side effects you should be aware of? There's no need to keep wondering, "Does Epsom salt kill ants?" -- this handy guide will answer all your questions!

Read more
This is how to know when to harvest your peas for maximum flavor and crispiness
Find out when your peas are just right for the picking
Organic green sugar snap peas

If you're looking to start a vegetable garden or just add to the one you already have, consider growing peas. These green pods are some of the easiest spring vegetables to grow — they even work as indoor vegetables. They tolerate cold temperatures and moist conditions quite well and don’t need much fertilizer to thrive. Best of all, their crisp texture and sweet flavor make them versatile veggies in the kitchen. The only thing that's tricky about growing peas is knowing when to time your harvest. If you're having trouble figuring out when to harvest peas, keep reading to know when to get the freshest, sweetest, and crispest peas.

Quick tips on growing peas
Even before you get to harvesting, you want to care for your peas so they grow healthy, strong, and delicious — luckily, they're pretty low-maintenance vegetables. Here are some tips to start your pea-growing journey:

Read more