Black widow spiders pose a significant health risk due to the potent neurotoxin in the female’s venom. Finding an egg sac indicates a potential infestation of hundreds of spiderlings, requiring immediate action to prevent their dispersal. The effective destruction of black widow egg sacs is a primary step in managing these populations around a dwelling. This guide outlines the necessary steps for identifying these sacs and employing various physical, chemical, and environmental control methods.
Identifying the Black Widow Egg Sac
Accurate identification is the first step toward safe removal, requiring protective gloves and long sleeves before inspection. The black widow egg sac is distinct, appearing smooth and papery with a spherical or pear shape. Its color ranges from off-white to light tan or grayish, measuring approximately 9.5 millimeters in diameter (the size of a large pea or small marble).
The sac is often suspended within the female’s irregular web, usually located in a dark, sheltered, and undisturbed location. Common sites include wood piles, under decks, crawl spaces, and cluttered areas of garages or sheds. Unlike the fluffy or spiky sacs of some other spiders, the black widow’s sac has a uniformly tight, well-defined silk structure. A single female can produce multiple sacs, each containing several hundred eggs that hatch after 20 to 30 days.
Immediate Physical Destruction Techniques
Vacuuming is the most recommended and safest immediate removal technique, minimizing the risk of the sac rupturing and releasing spiderlings indoors. Use a vacuum with a hose attachment to reach the web from a safe distance, ensuring you suck up the entire sac and any nearby adult spiders. For optimal containment, a HEPA-filtered vacuum is preferred.
The vacuum bag or canister contents must be managed immediately after use. The sealed bag should be placed in a plastic bag and disposed of in an outdoor trash receptacle. Alternatively, the contents can be frozen for several days to ensure they are dead before disposal.
A direct crushing method can be employed for sacs found outdoors or on hard, non-porous surfaces, using a sturdy, long-handled object like a shoe or shovel. Confirmation that the sac has been thoroughly flattened is necessary, as the thick silk covering offers substantial protection. Avoid crushing the sac on a soft surface or indoors, as this increases the likelihood of immature spiderlings escaping.
For non-vacuum removal of an accessible sac, scrape it gently into a jar or heavy-duty plastic bag using a stick or broom. Once contained, the sac can be sealed and submerged in rubbing alcohol for a few hours, which penetrates the silk and kills the contents. Alternatively, the sealed jar can be placed in a freezer for at least 72 hours before being discarded.
Chemical and Residual Treatment Options
Chemical control offers both contact destruction and long-term residual prevention, though the sac’s thick silk casing presents a barrier to many products. When using aerosol sprays, select an oil-based product. Since the silk is naturally water-repellent, water-based pesticides are less effective against the eggs inside. Direct and heavy saturation of the sac is necessary to ensure the chemical penetrates the protective layers.
Residual insecticides are often liquid concentrates applied to foundation perimeters, window frames, and other exterior entry points to create a protective barrier. These products establish a long-lasting residue that kills adult spiders and newly dispersed spiderlings that cross the treated surface. Always strictly adhere to the product label instructions, especially regarding application rates and safety precautions around children and pets.
Insecticide dusts provide effective residual treatment for hard-to-reach void areas where black widows often nest, such as wall voids, attics, and crawl spaces. Dusts like diatomaceous earth or products containing deltamethrin are applied into cracks and crevices, remaining active for extended periods. These dusts do not immediately kill the sac but are effective at killing spiderlings shortly after they hatch and leave the protective silk casing.
Habitat Modification for Control
Long-term control relies heavily on making the environment less appealing to spiders, preventing future nesting and egg-laying. Reducing clutter is a straightforward and highly effective step, as black widows seek dark, protected spaces for their webs and egg sacs. Removing debris, old boxes, loose lumber, and stored items from garages, basements, and the home’s exterior eliminates numerous potential nesting sites.
Sealing structural gaps prevents black widows from gaining access to indoor harborage areas. Inspect the foundation, walls, and utility entry points for cracks and holes, sealing them with caulk or weatherstripping. This physical exclusion reduces the number of dark crevices where a female might suspend her egg sac.
Adjusting exterior lighting can also reduce the spider population by limiting their available food source. Night-flying insects attracted to outdoor lights provide sustenance for adult spiders. Switching to yellow or sodium vapor bulbs, which are less attractive to insects, decreases the spider’s prey availability and encourages them to relocate.