Bagworm, Thyridopteryx ephemeraeformis, is the bane of arborvitae lovers and over a hundred other species of trees and shrubs. The clandestine caterpillars weave silken bags that are easily mistaken for pinecones. Then the pests carry them around like sleeping bags, wreaking havoc. But how do you get rid of bagworms on Arborvitae?
The method of getting rid of bagworms on Arborvitae is to remove the bags by hand. Spraying with Bt (Bacillus thuringiensis) can help if the worms have just hatched. As a last resort, there are chemicals such as Spinosad, which are sadly toxic to bees.
While a single season’s worth of a bagworm infestation will probably not kill your Arborvitae, it does cause damage and weakens the tree. However, a repeated infestation can kill. Therefore, catching bagworm early is key to successful eradication. That means knowing how to spot these camouflage artists.
What Are Bagworms?
Bagworms are not worms but the larva (caterpillars) of the Psychidae family in the Lepidoptera. So, to put that in plain English, bagworms are baby moths.
There are over a thousand varieties of bagworms, but the most common in North America are Thyridopteryx ephemeraeformis. These bagworms love eating Arborvitae, along with juniper, spruce, pine, and cedar. They can live on deciduous trees, too, but they are not the first preference.
Female bagworms never leave their bag. It is only adult males that can fly. However, the real spread across your garden occurs when the caterpillars are young. They will make silk strands to create a “parachute, “allowing the wind to carry them to a new location. This is called “ballooning.”
However, larger caterpillars can crawl to a new plant, too, if branches are touching.
Bagworm Life Cycle
The lifecycle of bagworms is pretty predictable. Mating is in early fall. Then, the male moths fly around, looking for females in their bags. The females lay hundreds of eggs into their bags and then die.
Then the bag hangs from its branch from late fall through winter, like a mountain climber bivouacking from a cliff face. Come spring, they hatch and begin to eat and eat and eat, over six weeks.
Adult bagmoths do not have long lives. The females live for about a week, the males around two days. None of the adults eat.
The period of destruction to Arborvitae and other foliage is that six-week span the caterpillars are gorging themselves, preparing for metamorphous.
How to Identify Bagworms?
The easiest way to identify a bagworm is by its bag. Unfortunately, these are often mistaken for pinecones at a distance. It is therefore recommended that you closely inspect any “pinecones” or “brown clumps” on your Arborvitae along with other trees and shrubs from late fall through winter.
The bags of bagworms are made up of silk and foliage, often from the tree, they inhabit. Due to the dead foliage, these conical cocoons are brown and will be between 1.5-2 inches in length (3.8-5.08 cm). They are fastened to the plant by silk.
If you are ever in doubt if what you are looking at is a pinecone, part of the tree, or a bagworm, cut one off and slice it open. (You might want to wear gloves, but totally up to you.)
If it is a bagworm, you’ll be left looking at a black-ish worm-like-critter or a bunch of tiny, yellowish, squishy eggs in a goo that is might be the remains of dear old mom. (Depending on the bagworm species, the adult female either goes off to die or mummifies in her bag with the eggs.)
If it isn’t a bagworm, then you are either sawing away at a pinecone or might have a very sticky spider’s nest, and… that’s a whole different post. (Bagworm nests really don’t look like spider nests.)
3 Ways to Get Rid of Bagworms
A bagworm infestation can easily snowball, so the best way to shut them down is to spot them early. This is why checking your Arborvitae and other foliage from fall through winter is so important because the best time to nip an infestation is before they hatch.
1 – Hand Removing Bagworms
The best way to deal with bagworms is to pick them off the foliage by hand and destroying the bags. Again, we suggest gloves.
Ideally, you want to pick them off before they hatch, so they never get a chance to munch or mate. But there is no wrong season to remove a bagworm’s bag.
Hand removal isn’t just better for the environment; it is also more effective. Unfortunately, other methods might not kill them all, and some pesticides have been proven to accelerate the pupate process (not helpful).
Removing by hand is painstaking work. You not only want to remove the bag, but also the silk wrapped around the branch as this too can harm the tree as it grows. There are pest controllers that specialize in this if you do not feel up to the task.
You need to get all the bags off the infected foliage. As mentioned above, females can lay a lot of eggs, between hundreds up to a thousand. So one missed bag can create another cycle of problems.
On the bright side, you don’t need to stress about any flittering adult males. They don’t transport eggs, and as mentioned above, they don’t eat.
After you believe you’ve removed every bag from the infected foliage, give the plant(s) a good, hard hose down. This might knock off any overlooked bags.
2 – Bt Removal of Bagworms
Bt (Bacillus thuringiensis) is bacteria that is naturally found in soil. It is toxic to certain critters, such as bagworm larvae, but doesn’t hurt humans, birds, fish, or earthworms.
Most Bt doesn’t harm honeybees, but the aizawi is toxic to bees. Thus, we suggest using a bee-safe Bt, such as kurstaki strain. Kurstaki is considered to be the best strain of Bt to eliminate caterpillars, anyway.
Commercial Bt is found in a wide variety of products, including organic or “eco” sprays. But, again, it is crucial to check the strain of Bt used, as not all of them are considered effective against caterpillars.
A number of commercial brands of kurstaki Bt are bluntly sold as Caterpillar killers, such as Summit’s Caterpillar and Webworm Control. Other common commercial names that sell kurstaki Bt are Dipel, Thuricide, and Monterey Bt.
The timing of spraying Bt is crucial to the success of eradicating bagworm. Bt works best when the caterpillars are newly hatched. Depending on where you live, bagworms hatch from May into early June.
Bt does nothing to the bags of eggs or pupae. The caterpillar must eat bt to work, and the younger it is, the more suitable it is to the bacterial.
3 – Chemically Removing Bagworms
Your last resort to fighting bagworms should be chemicals. This is because they endanger bagworms’ natural predators, including birds feasting on the insects and caterpillars, including bagworms.
Generally, your chemical sprays have to be used during that spring period of May and June, just like Bt. Those bags that bagworms build are very good chemical-proof-vests.
The chemically generally work by making contact with the actual larva or by being consumed. Again, this makes the chemical methods near pointless during the majority of the bagworm lifecycle.
Like Bt, all of the following work best when the bagworm is young. It is tough to do anything about the situation after the bagworm larvae (not its bag) is bigger than half an inch (1.27 cm).
Chemical Treatments For Bagworm
The following are a list of chemicals used to treat bagworm. Please note, these products are often sold under commercial names or mixed into other commercial products.
Some items listed may also be banned in your part of the world. Always check before use.
Acephate is a popular organophosphate insecticide often used on golf courses and citrus trees. Its use is generally restricted and not recommended to be used around homes.
It is not safe to use around pets and harms birds. Anyone using this stuff must wear protective gear, including masks, as it can make you feel very unwell. In addition, it has been known to give children seizures.
It works by both making physical contact with the caterpillar and be being ingested.
Azadirachtin is better known as neem oil. It is generally safe for birds, fish, bees, and other wildlife.
However, while it is a safer choice, that doesn’t make it safe to use in any manner and any quantity. Misuse of neem oil led to the substance being banned in Canada.
It works mainly as a stomach poison, especially in regard to caterpillars. Some soft body insects, however, are suffocated by the substance when it’s applied.
Bifenthrin is a common insecticide. It is a manmade pyrethrin. Natural pyrethrin can be found in chrysanthemums.
Bifenthrin is toxic to fish and bees. In addition, because it can accumulate in fish, it is a potential risk to birds and other animals that eat fish. Birds that don’t eat fish, however, are not considered at risk.
Bifenthrin causes problems with the insects’ nervous systems when insets touch or eat it.
It is toxic to fish, earthworms, shrimp, and honeybees. However, it is only considered slightly toxic to birds and moderately to mammals.
Also, while a plant’s leaves absorb very little carbaryl, the same cannot be said when it encounters the root system.
Carbaryl disrupts an essential nerve enzyme, thus disrupting the breathing muscles of pests. Therefore, it needs to be digested or at least reach the skin.
Cyfluthrin is pyrethroid insecticide.
Like other pyrethroids, it is toxic to bees and fish. Nor is it advised to be used by people with asthma.
Like Bifenthrin, it kills the caterpillar by interfering with the nervous system
Gamma-Cyhalothrin is another manufactured pyrethroid insecticide.
It is not only a groundwater contaminator; it will also accumulate in milk and other tissues. In addition, it is highly toxic to bees, green algae, and fish.
It kills caterpillars in a similar manner to Bifenthrin.
Malathion, also known as carbophos, is an organophosphate often used to control mosquitos. It is banned in some countries.
It is highly toxic to bees and some fish and moderately toxic to birds and some fish.
Like many insecticides, it impacts the nervous system. It can have an impact if breathed in or consumed.
Permethrin is the active ingredient in Nix and many other medications used to treat lice or scabies. It is a pyrethroid, like some others that are listed.
Permethrin is used to spray crops, livestock, and on pets (think flea collars). It is toxic to fish and bees.
Like other pyrethroids, permethrin has to come into contact with the bagworm (not just their bag) or be ingested to harm the pests.
Spinosad is one of the most popular chemical remedies to fight bagworm. Like Bt, it’s produced by a soil bacterium.
While Spinosad is natural and even used by some in organic agriculture, it is toxic to bees. The risk reduces once it has dried, however.
But because the world’s pollinators are under such threat, it is banned in some places, and the cannabis industry generally forbids its use.
Like Bt, it must be ingested to work against caterpillars.
Bagworm Control And Prevention
Routine inspection of plants, especially trees, is crucial to keeping bagworms from becoming a problem in your garden and yard. Also, inspect any branches of any new trees you bring onto your property before planting.
The next best defense against bagworms is natural predators. Birds, especially woodpeckers and sparrows, will devour bagworms with pleasure. Other birds that enjoy bagworms are chickadee, nuthatch, and titmice.
Make your property bird-friendly by avoiding pesticides that destroy all insects. Also, make sure any insect control or repellents used are safe for birds.
Ants and spiders eat bagworm eggs and make good food for birds. Vespid wasps and hornets are other bagworm predators.
You can attract a diversity of helpful insects, which birds need, by ensuring you’ve planted a diverse selection of plants, including ones that flower at different times of the year.
You can also put up bird homes around your property, including ones designed to specifically attract certain species.
Woodpecker boxes are most successful when put up in the fall. They need to be 6 to 16 feet (2-5 m) into a tree or on a pole hidden amongst the foliage of your Arborvitae hedge.
Woodpeckers instinctively need to clear out a new home before they “build” for their young. Thus, to raise the likelihood of your box being chosen, fill it with woodchips.
Sparrows like their box placed under eaves. The box should face somewhere between north and east. There should be nothing obstructing the flight path to the home’s entrance.
Sparrows prefer to live and nest in colonies. So there needs to be two to three boxes lightly spaced out but in the same general area.
Monitoring your Arborvitae over fall and winter while promoting natural predators is your best defense against bagworms. Should you find any bagworms, grab some gloves and start picking.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.