You’re standing in your garage or peering into the dark corner of your basement, and there it is—a massive, multi-legged tenant paying zero rent. It’s natural to want a quick fix. You’ve probably heard from a neighbor or a random forum that tossing a few white spheres into the corner will do the trick. But do mothballs keep spiders away? Honestly, the answer is a resounding "no," and using them might actually cause more trouble than the spiders ever could.
It’s a persistent old wives' tale. People assume that because mothballs have a pungent, chemical odor that makes humans cringe, they must be a universal repellent for everything with more than four legs. Spiders aren't moths. They don't eat your wool sweaters, and their biology is fundamentally different from the pests mothballs were actually designed to kill.
What exactly is in a mothball?
To understand why this doesn't work, you have to look at the chemistry. Most mothballs are made of almost pure naphthalene or paradichlorobenzene. These are solid chemicals that turn into a gas at room temperature—a process called sublimation. The goal is to create a high concentration of toxic vapor in a sealed, airtight container to kill clothes moths and their larvae.
Spiders are different. They are arachnids, not insects. They breathe through "book lungs" or tracheae, and they are notoriously hardy. A spider walking over a mothball in a drafty basement isn't going to be bothered by the fumes because the air isn't concentrated enough to affect them. Unless you’re planning on sealing yourself in a plastic bag with a box of naphthalene—which, please, never do—the spiders are just going to keep on spinning their webs.
The real danger of the "DIY Repellent" approach
There's a reason the Environmental Protection Agency (EPA) is so strict about mothball labels. Using them to repel spiders, snakes, or mice is actually an illegal use of a pesticide. It sounds dramatic, but the "label is the law." When you scatter mothballs in an open area like an attic or a crawlspace, you aren't just targeting spiders. You’re off-gassing chemicals into your home’s HVAC system.
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Naphthalene is a suspected carcinogen. Long-term exposure to these vapors can lead to headaches, nausea, and dizziness in humans. If you have pets or toddlers, the risk is even higher. To a dog or a small child, a mothball looks like a piece of candy or a fun toy. Ingesting just one can cause hemolytic anemia, where the body starts destroying its own red blood cells. It's a high price to pay for a "remedy" that doesn't even work on the spiders.
Why spiders don't care about your mothballs
Spiders are predators. They follow the food. If your house has a lot of spiders, it's because your house has a lot of other bugs—flies, moths, ants, or crickets. Spiders are the "clean-up crew" of the ecosystem.
A mothball sits on the floor. A spider usually hangs out on the ceiling or in a high corner. Since the toxic vapors from naphthalene are heavier than air, they sink. The spider literally lives in a different atmospheric zone than the repellent. Even if the spider did come into contact with the smell, it doesn't have the same sensory receptors that a moth does. It doesn't find the smell "gross"; it just finds it irrelevant.
What actually works for spider control
If you want to clear out the webs, you have to get a bit more strategic. Forget the chemicals for a second and look at the "Three S's": Seal, Sweep, and Sunlight.
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Seal the gaps. Spiders aren't teleporting in. They come through the gaps under your doors, the cracks in your window screens, and the holes where cables enter your siding. A $5 tube of silicone caulk will do more for your spider problem than a hundred boxes of mothballs ever will.
De-clutter. Spiders love "undisturbed" areas. That stack of cardboard boxes in the corner? That’s a luxury apartment for a Brown Recluse or a common House Spider. Switching to plastic lidded bins makes your storage less attractive to pests.
Manage the light. This is a trick most people miss. Spiders aren't necessarily attracted to light, but their food is. If you have a bright porch light on all night, you’re inviting a buffet of moths and beetles. The spiders just set up their nets where the fish are biting. Switch to yellow "bug bulbs" or motion-activated lights to reduce the insect traffic.
The Essential Oil alternative: Myth or Magic?
You'll often hear that peppermint oil is the "natural" version of the mothball trick. Some studies, including research published in the Journal of Economic Entomology, suggest that certain essential oils like peppermint or chestnut can have a repellent effect on specific spider species.
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However, there's a catch. These oils are highly volatile. You can't just put a drop in the corner and expect it to work for a month. To be effective, the scent has to be incredibly strong and refreshed almost daily. It’s a lot of work for a result that is, at best, temporary. It's certainly safer than naphthalene, but it's still a "band-aid" solution that doesn't address why the spiders are there in the first place.
When to call in the pros
Sometimes a spider situation gets out of hand. If you’re seeing a high volume of medically significant spiders—like Black Widows or Brown Recluses—it might be time to skip the DIY hacks. A professional pest control operator won't just spray; they’ll identify the entry points and the secondary infestation (the "food") that’s drawing the spiders in.
They use targeted residual pyrethroids or desiccants like Diatomaceous Earth in wall voids. These methods are designed to stick to the spider's legs. Since spiders groom themselves by pulling their legs through their mouthparts, they ingest the treatment. A mothball sitting on the floor never gets "on" the spider, which is why it fails every time.
Better ways to use your energy
Stop buying mothballs for anything other than moths in airtight trunks. If you’re worried about spiders, go grab a vacuum with a long attachment. Suck up the webs and the egg sacs. It’s immediate, chemical-free, and 100% effective.
Next Steps for a Spider-Free Home:
- Inspect your weather stripping: If you can see daylight under your front door, a spider sees a grand entrance.
- Clear the perimeter: Keep mulch, woodpiles, and heavy vegetation at least two feet away from your home's foundation.
- Check your humidity: Spiders and their prey love damp environments. Running a dehumidifier in a musty basement can make the area far less hospitable to the entire food chain.
- Ditch the cardboard: Move your seasonal decorations into plastic totes to eliminate hiding spots.
The reality is that spiders are mostly harmless and even helpful. But if you want them out, do it safely. Mothballs are a health hazard in the making, and they won't stop a single spider from building a web right above them.