Those small, spindle-shaped cases clinging to your house walls, ceilings, or siding are almost certainly the portable homes of bagworm moth caterpillars. Two different species commonly show up on and inside houses: the household casebearer (often called the plaster bagworm), which lives indoors and on exterior walls, and the evergreen bagworm, which feeds on trees and shrubs but sometimes attaches to siding, fences, and decking when it’s ready to pupate. Both build distinctive silk cases reinforced with debris, and both are easy to manage once you know what you’re dealing with.
What the Cases Look Like
The household casebearer builds a flat, oval case roughly the size and shape of a watermelon seed. The silk exterior gets covered with bits of sand, lint, paint flakes, and other fine debris from whatever surface the caterpillar crawls across. You’ll find these cases hanging from ceilings, curtains, subflooring, joists, exterior walls in shaded spots, and under outdoor furniture. They’re lightweight enough to cling to smooth surfaces and easy to mistake for random bits of debris until you notice dozens of them.
Evergreen bagworms build a different structure: a tapered, cone-shaped bag that can reach about two inches long when fully grown. These bags are covered in bits of needles, leaves, and twigs from whatever plant the caterpillar has been feeding on. When you spot them on your house, they’re typically attached to siding, window frames, wooden fences, or decking rather than inside the home. The caterpillars sometimes wander away from their host trees to find a spot to pupate, which is how they end up on buildings.
Why They Show Up on Your House
Household casebearers are drawn indoors by food. Their primary diet is old spider webs, which they consume in large quantities. They also eat the dried insect parts caught in those webs. Beyond spider silk, they feed on wool, animal-based fibers, feathers, and accumulations of human hair and dandruff. A house with undisturbed spider webs in corners, along baseboards, or under furniture is essentially a buffet for these caterpillars. Exterior walls attract them for the same reason: sheltered, shaded spots tend to accumulate webs.
Evergreen bagworms end up on houses for a different reason entirely. They spend most of their lives on trees and shrubs, feeding on foliage from June through late July or August. When they’re ready to pupate, they sometimes leave their host plant and attach to the nearest solid surface, which can be your siding, deck railing, or fence. They aren’t feeding on your house. They’re just using it as an anchor point for the pupal stage.
Life Cycle and Active Months
Evergreen bagworms produce one generation per year. Overwintering eggs hatch inside the mother’s bag in early June, and each tiny larva immediately starts building its own silk case. For the first few weeks, the bags stay small, under a quarter inch, making them hard to spot. The caterpillars feed and molt through the summer, then pupate in August. Adults are active in late August and September. Only males actually leave the bag to fly and mate. Females stay inside their bags, lay eggs there, and die, meaning the bags you see on your house in fall and winter may contain hundreds of eggs ready to hatch the following June.
Household casebearers in warm, humid climates like Florida and the Gulf Coast can be active for a longer portion of the year, since they live in temperature-controlled indoor environments or sheltered exterior spots. You may notice them on walls and ceilings throughout the warmer months.
Can They Damage Your Home or Belongings?
Household casebearers are classified as potential household pests because of their appetite for animal-based fibers. In lab studies, when offered woolen threads and woolen cloth, the caterpillars ate eagerly. They can feed on wool rugs, wool carpets, silk, felt, and similar materials. On rare occasions, they damage clothing and other fabrics. That said, their strong preference for spider webs means fabric damage is uncommon unless you have a large population and unprotected woolens in storage.
Evergreen bagworms pose no risk to your house itself. They don’t eat wood, paint, or siding. The concern with these caterpillars is the trees and shrubs in your yard, especially evergreens. A heavy infestation can strip a conifer of its needles, and unlike deciduous trees, evergreens often can’t recover from severe defoliation.
How to Remove Them
The simplest approach for both species is physical removal. Pick or scrape the cases off walls, ceilings, siding, and other surfaces and drop them into a bucket of soapy water. For evergreen bagworms attached to your house, this is really all you need to do on the structure itself. If you remove them before eggs hatch in early June, you prevent the next generation entirely. Check nearby trees and shrubs for additional bags and pull those off too.
For household casebearers indoors, removal works best alongside cleaning. Vacuum thoroughly along baseboards, in corners, behind furniture, and anywhere spider webs accumulate. Clearing out webs removes both the casebearers’ food source and their preferred habitat. Pay attention to closets and storage areas where wool, silk, or other animal fibers are kept. Sealing woolens in airtight containers or bags eliminates them as a food source.
Reducing outdoor lighting or switching to yellow bulbs can also help. Adult moths are attracted to lights at night, and fewer moths near your home means fewer eggs laid on or near your walls.
When Chemical Treatment Makes Sense
For a handful of cases on your house, hand-picking is more effective than spraying. Chemical treatments are worth considering when evergreen bagworms are actively feeding on landscape plants, especially valuable evergreens. The key is timing: sprays work best against young caterpillars in June and early July, when the larvae are small and actively eating. By August, when the caterpillars are larger and starting to pupate, sprays become far less effective.
The gentlest effective option is Bt (Bacillus thuringiensis), a naturally occurring bacterial product that targets caterpillars specifically. The caterpillar ingests it while feeding and stops eating within hours. Spinosad, derived from a soil bacterium, is another lower-risk option that’s less harmful to pollinators than broad-spectrum alternatives. Pyrethrin-based sprays provide faster knockdown for heavier infestations. Neem oil and insecticidal soap can work on very young caterpillars but need direct contact.
Keeping Them From Coming Back
For household casebearers, prevention is mostly about housekeeping. Regular vacuuming and web removal eliminate their primary food source. In humid climates, reducing indoor humidity with a dehumidifier makes your home less hospitable. Sealing cracks around windows, doors, and utility penetrations limits entry points for both caterpillars and the moths that lay eggs inside.
For evergreen bagworms on your house exterior, the main strategy is managing the population on nearby plants. Inspect trees and shrubs in late fall or winter when the bags are most visible and strip them off before spring. Each bag left on a branch can release hundreds of tiny caterpillars the following June. Even a single season of thorough hand-removal can dramatically reduce the next year’s population, and the bags are much easier to spot after deciduous plants drop their leaves.