Are leaves turning brown in your trees well before autumn? Are needles falling off the pine trees? Have you noticed clumps of pine needles or brown leaves hanging off branches?
You may have bagworms.
What are bagworms?
Also known as evergreen bagworm, eastern bagworm, and common bagworm, the bagworm (Thyridopteryx ephemeraeformis) is a moth species, although you probably won’t see them flying around any time soon.
As the caterpillar larva feeds on the host tree, it spins a silken case around itself. Leaves or needles from the host tree stick to the case, camouflaging it from sight.
The leaves and needles brown from the bottom up. Once the entire case is brown, the caterpillar has either died or emerged as a moth.
Unfortunately, once you have a couple in your tree, populations explode quickly. Female moths can lay up to 1,000 eggs at one time within their casing.
They’re most commonly found in the Eastern United States, as far west as Nebraska, and south through the Gulf of Mexico through Texas.
What do bagworms look like?
You’ll rarely see the caterpillar itself, but you can spot their casings. These cases are around 1.5 to 2.5 inches, constructed out of the tree’s leaves or needles in a conical shape. The casing will look different based on the tree species.
Adult male bagworm moths look like pretty unremarkable, brown-furred moths. Adult females never leave their casings, so they look like caterpillars.
Where do bagworms come from?
Female moths lay their eggs within their casings in late summer, then die. The eggs survive the winter in the casing. The new larvae emerge in June to feed on their host plant.
Bagworm caterpillars can either drag their casing to a new location or spin a silk web that carries them to new trees.
Damage caused by bagworms
Bagworms attack all kinds of trees but prefer cedar and juniper. They begin at the top of their host tree, and while they’re very young, the damage is just some light patches on the leaves.
But as the larvae mature, they consume entire needles or leaves. They can strip an entire tree.
Healthy deciduous trees can survive this by producing another set of leaves. Evergreens cannot, and they usually die.
An introduction to bagworms and how to eliminate them:
How to get rid of bagworms
Handpick in the fall or early spring
As with all pests, the secret to keeping bagworms under control is to catch them early. Bagworms make this easy because the females lay their eggs within the casing, which then overwinters so the larvae can emerge in June.
If you check your trees regularly in the autumn, winter, or early spring, you can simply remove the trees’ casing before they hatch. As each casing can contain up to 1,000 eggs, you can see how this bit of prevention will save you a ton of trouble later on.
You can also check your trees throughout the summer, handpicking and destroying casings as you find them.
Encourage birds in your yard
If you’re looking for a preventative measure, encourage sparrows to come into your yard as they eat bagworms. Add a birdbath low to the ground, brush piles and shrubberies that sparrows can flit between, and a patch of dust for dust-bathing.
Sapsucker woodpeckers will also eat bagworms for you. Chickadees, nuthatches, and titmice will scavenge bagworm eggs during the winter, so keep up the birdfeeder to encourage these birds to stick close.
Plant Aster family flower borders to attract parasitic wasps
Ichneumon wasps are another natural predator, laying their eggs in bagworm caterpillars. If, like me, you have a massive fear of wasps — don’t worry.
These wasps are tiny and don’t sting humans. Plus, they take care of a wide range of pest problems, from beetles to caterpillars.
Ichneumon wasps prefer Aster family flowers, so planting some will attract the wasps. In one trial, planting a flower border around bagworm host trees led to a 70% increase in parasitized bagworms (that means 70% of an infestation taken care of).
Aster family flowers include sunflowers, Black-Eyed Susan, daisies, chrysanthemums, marigolds, and dahlias. All flowers I’d love to have in my yard, even without the fringe benefits.
If you are desperately in need of wasp help, then you can purchase parasitic wasps online and release them in your garden. They come as eggs on a card, which you simply place in your garden.
Adding their favorite flowers will encourage them to stick around for continued prevention even once they’ve taken care of the bagworms.
Plant less susceptible trees
While bagworms will eat pretty much all kinds of trees, they favor cedar. So if you get infestations every year, plant different trees. Broadleaf evergreens show less damage. Deciduous trees can bounce back even after a severe attack.
And planting different species of trees will also encourage birds that prey on bagworms to visit your yard.
Apply Bacillus thuringiensis (Bt)
If the bagworms are just hatching in June, you can spray the foliage with bacillus thuringiensis. Unlike other pesticides, Bt doesn’t kill on contact. Insects have to ingest it. Once ingested, the insect dies of infection and starvation within hours or even days.
It doesn’t kill all insects, but on the downside, it’ll probably kill any other butterflies and moths whose food source comes into contact with Bt. Spray carefully, and only if you really must.
Bt is less effective as the caterpillar grows larger.
Bagworm infestations can get out of control quickly, but thankfully, with a bit of preventative action during the winter and encouraging predators into your yard, you can keep that from happening.