Spiders are killed by pyrethroid insecticides like bifenthrin, deltamethrin, lambda-cyhalothrin, permethrin, cyfluthrin, and cypermethrin, plus pyrethrins and tetramethrin, but only when the product’s EPA-approved label lists spiders.
Soak a spider’s harbor with a pyrethroid and re-invasion from cracks, door gaps, and prey insect populations can undo the work in weeks. Utah State University Extension identifies deltamethrin, lambda-cyhalothrin, permethrin, pyrethrin, and tetramethrin as the most common spider-control ingredients, and specific formulations expand this list. Choosing between them starts with what the label permits, not with what the bottle’s marketing name suggests.
Which Ingredients Are Verified To Kill Spiders?
Nine active ingredients are documented for spider control, led by the synthetic pyrethroids, with pyrethrins offering contact kill only.
- Bifenthrin — a synthetic pyrethroid; the EPA label for Bifenthrin RTU (EPA Reg. No. 53883-185, July 25, 2024) lists spiders including black widow, brown recluse, and daddy longlegs.
- Deltamethrin — used in residual sprays and aerosols.
- Lambda-cyhalothrin — a residual pyrethroid listed by Utah State University Extension.
- Permethrin — another Extension-listed spider ingredient, common in outdoor formulations.
- Pyrethrins — natural pyrethrum-derived, killing on direct contact with no lasting residual.
- Cyfluthrin, cypermethrin, tralomethrin, and tetramethrin — control spiders when applied per label directions.
Residual pyrethroids work best in labeled cracks, crevices, baseboards, voids, window corners, garages, and basements. Sunlight shortens outdoor persistence.
Where Does The Label Say To Spray?
The Bifenthrin RTU label directs application in specific indoor and outdoor harbor sites, and the label—not the retailer’s shelf tag—controls every legal use.
The July 2024 EPA label lists room and closet corners, wall cracks and crevices, baseboards, beneath and behind refrigerators, stoves, sinks, and cabinets, around plumbing pipes and fixtures, and around door and window frames. Bifenthrin falls in Insecticide Resistance Action Committee Group 3A.
The label also governs dilution, application rate, reentry intervals, ventilation, storage, disposal, and restricted sites. Two bottles with the same active ingredient can carry materially different legal directions, so check the EPA registration number, active-ingredient percentage, target pest list, and use sites before buying.
| Active Ingredient | Residual Control | Best Labeled Use |
|---|---|---|
| Bifenthrin | Yes | Cracks, baseboards, voids, indoor and outdoor |
| Deltamethrin | Yes | Residual sprays and aerosols |
| Lambda-cyhalothrin | Yes | Structural perimeter and harbor treatments |
| Permethrin | Yes | Outdoor perimeter and labeled indoor sites |
| Cyfluthrin | Yes | Labeled indoor and outdoor sites |
| Cypermethrin | Yes | Labeled structural application |
| Pyrethrins | No | Direct contact kill, knockdown only |
| Tetramethrin | No | Aerosol knockdown per label |
For readers comparing ready-to-use formulas for gardens and perimeters, the tested breakdown of insecticides for spiders outdoors ranks products on residual life and labeled use sites. The EPA’s Bifenthrin RTU product label remains the authority on where any bifenthrin product may legally go.
What Mistakes Waste A Spray?
Most failed spider treatments come from five avoidable errors, and each one costs either money or safety.
- Buying an insecticide that never lists spiders on its EPA-approved label—”insects” coverage is not spider coverage.
- Spraying webs alone while ignoring cracks, crevices, door gaps, vegetation, and the insect prey that draws spiders inside.
- Expecting pyrethrins to hold a harbor for weeks; they give contact kill only.
- Confusing spiders with spider mites, plant-feeding arachnids that need miticides such as abamectin, hexythiazox, or spiromesifen—some restricted to commercial ornamental use.
- Applying outdoor formulatas indoors, or indoor products to edible plants, without explicit label authorization.
Safety follows the same rule. Pyrethroids are broad-spectrum, so apply only to labeled voids, cracks, crevices, and baseboards; cover or remove food, dishes, utensils, pet food, and exposed aquariums where the label requires; keep people and pets away for the label-specified interval; avoid drift and runoff; and ventilate treated indoor areas as directed.
Common Questions
Do pyrethrin sprays keep killing spiders after they dry?
No. Pyrethrins kill spiders on direct contact but leave no meaningful residual, so a spider that walks across the surface days later is unaffected. For lasting protection in cracks, crevices, and baseboards, choose a residual pyrethroid such as bifenthrin, deltamethrin, or lambda-cyhalothrin and apply it exactly as the label directs.
Can one bottle of spider spray be used both indoors and outside?
Only if the EPA-approved label explicitly authorizes both. Some residential products, including Bifenthrin RTU, carry indoor and outdoor site listings, while others cover a single use site. Read the use-sites section on the label itself rather than the store description, and never move an outdoor formulation inside or apply an indoor product to edible plants without label authorization.
Will spider insecticide also eliminate the webs in my garage?
It kills spiders, not their webs. Knock down webs with a broom or vacuum first, then treat the labeled harbor areas—wall cracks, baseboards, window corners, and voids—where spiders hide. Removing webs without treating those gaps usually means spiders rebuild within weeks, so combine physical cleanup with a residual application on the labeled sites.
Sources
- Utah State University Extension. “Spiders” Identifies deltamethrin, lambda-cyhalothrin, permethrin, pyrethrin, and tetramethrin as common spider-control ingredients.
- US EPA. “Bifenthrin RTU Pesticide Product Label, EPA Reg. No. 53883-185, July 25, 2024” Supports the labeled spider species, application sites, use restrictions, and Group 3A classification.