Grass spiders (Agelenopsis) are common North American funnel-web builders frequently encountered in lawns and around homes. Their webs are distinctive, appearing as sheet-like silk structures stretched across the ground or low foliage, often with a funnel-shaped retreat where the spider waits. These spiders often move indoors during the late summer and fall, seeking shelter. The following strategies focus on practical methods for eliminating grass spiders and modifying the environment to prevent their recurring presence.
Identifying Grass Spiders and Assessing Risk
Grass spiders are identified by their physical characteristics and unique web design. They are generally brown or grayish with prominent longitudinal stripes on their cephalothorax, the fused head and chest section. A distinguishing feature is their noticeably long, paired spinnerets, which extend visibly beyond the end of the abdomen. Their size ranges from about one-third to three-quarters of an inch in body length.
The funnel web they construct is non-sticky and relies on a network of threads to trip and direct prey into the funnel retreat. Grass spiders are not considered medically significant pests to humans. While they possess venom, their mild venom and small fangs mean a bite is rare and typically results in only minor, localized symptoms like slight swelling or itching.
Making the Environment Unsuitable for Spiders
Modifying the habitat around your home is an effective method for deterring grass spiders. These spiders build their webs in areas that offer cover, such as dense vegetation, woodpiles, and debris near foundations. Removing these harborages makes the area less attractive for web construction.
Regular yard maintenance, including keeping the lawn closely mowed near the foundation, reduces available web-building space. Trimming back shrubs and ground covers that touch the structure eliminates bridging points spiders use to access exterior walls. Stored materials, such as firewood and garden clutter, should be moved away from the house to reduce sheltered resting spots.
Managing exterior lighting indirectly removes the spiders’ food source. Outdoor lights attract flying insects, which draw in grass spiders seeking prey. Switching to yellow or sodium vapor bulbs, which are less attractive to insects, diminishes the spider population.
Finally, sealing potential entry points around the foundation prevents spiders from moving indoors in the fall. Applying caulk to seal cracks, gaps around utility penetrations, and worn weatherstripping around doors and windows creates a physical barrier that excludes them.
Direct Contact and Residual Elimination Methods
Immediate removal of existing spiders and webs is best accomplished through physical means. The most direct method for destroying grass spiders and their entire structure is using a vacuum cleaner with a hose attachment. This removes the spider, its funnel web, and any potential egg sacs hidden within the retreat. Once vacuumed, the bag or canister contents should be sealed and immediately disposed of outdoors to ensure the spiders do not escape.
For a lasting effect, chemical and dust applications establish a residual barrier. Insecticidal dusts, such as diatomaceous earth (DE) or borate powders, are effective when applied to inaccessible areas like wall voids, cracks, and crevices. Diatomaceous earth works by damaging the spider’s protective outer layer, leading to dehydration and death, and remains active as long as it stays dry. When using DE, a very light dusting is necessary, as heavy application can cause spiders to avoid the area.
Residual liquid insecticides, often containing synthetic pyrethroids, are best used for perimeter treatment. Applying these products as a band around the foundation, window frames, and door thresholds creates a lasting chemical barrier that kills spiders attempting to cross the treated surface. Always follow the manufacturer’s label directions precisely for safety and effectiveness. Contact sprays, which use fast-acting ingredients like natural pyrethrins, can also be used for direct knockdown of visible spiders or for flushing them out of hiding spots.
When to Seek Professional Pest Control
While do-it-yourself methods are often successful for managing typical grass spider presence, certain situations warrant professional involvement. Persistent, large-scale infestations that return quickly despite repeated attempts at environmental modification and chemical application may indicate a deeper issue. This is especially true if the source of the infestation is inaccessible, such as within deep structural voids or complex underground areas.
A pest control technician can correctly identify the underlying cause, which may be a significant population of secondary insect pests attracting the spiders. Professionals have access to specialized equipment and restricted-use products that provide deep penetration into difficult-to-reach harborages. They can also apply micro-encapsulated formulations of residual insecticides that offer longer protection than consumer products. Seeking professional help provides expert diagnosis and a comprehensive treatment plan that targets both the spiders and their food source.