When I moved into a home that had a moderate brown recluse spider problem, I realized it would give me an opportunity to experiment a bit to see how each part of the control process might affect the numbers of spiders being seen or captured on traps. This article details some of my observations.
INITIAL SURVEY. When my wife and found this house, we fell in love with the layout and the room it afforded us for our comfort and hobby interests. My wife could have her own project room and I now have good-sized room to serve as my lab and photo studio. During the initial walk through of the house while we were deciding to buy it, I noted a couple of live recluse spiders in the bathrooms. I found a few more in the attic spaces, which is not surprising given that the vast majority of a recluse infestation resides in the periphery of a house — the wall voids, attic and crawlspace/basement (if present).
TRAPS & CATCHES. Upon closing, I came in and started the remodeling process. I placed insect monitoring traps in various spots in the attic, along walls and likely spider walkways. Traps also were placed along walls in all rooms of the house and the garage, behind each toilet, in each bath vanity and under the kitchen sink. Recluse spiders use wiring and plumbing lines to traverse through the walls and from the substructure and attic spaces. Placement of traps where plumbing lines exit walls is therefore a prudent trap location.
CARPETS & TRIM WORK. As I removed the old carpeting in several rooms, I would see one or two recluses. This discovery indicated to me that treatment along the tack strips under the edges of carpeted rooms should be considered for brown recluse spider control, depending on the severity of an infestation and the pest professional’s inspection.
I also found a couple of recluses when I removed trim from around doors and a couple of baseboards during my remodeling efforts. This confirmed the need to treat cracks behind trim around doors and windows and behind and under baseboards where accessible. In my case, most of the window and door trim and baseboards had been well caulked, and the only openings I would find were behind trim above doors and windows. These sites were treated using TriDie Silica & Pyrethrin Bulk Dust (BASF Corp.) and then sealed with a silicone sealant.
One place I noted recluse spiders living in numerous areas of the house was in cracks at the base of door frames. They were treated with dust and the cracks sealed with silicone sealant. Every crack under baseboards throughout the house was treated with dust.
KITCHEN. During the demo of the kitchen, I removed the countertop and cabinet doors as these would be replaced. Once everything was apart, I had access to see where voids were present between and behind the cabinets (see photo). The voids contained old comb-footed spider webs and some evidence of recluse spiders — a couple of cast skins and the wispy webbing recluse spiders will construct in the harborages. The voids between the cabinets and the side of the cabinet next to walls would not be accessible from the top when a counter is in place, but access could be made from the front underneath the overhang as these were open at the bottom.
Since mine were open, I treated each such void space using PT TriDie Pressurized Dust Insecticide equipped with a 4-way tip. If the counter had been in place, I would have treated from underneath the front of the cabinets.
Because recluse spiders also have access to the voids in the base under the cabinets, I drilled an 1/8-inch hole through the base plate of each cabinet closer to the top of the base where it would be less visible. Using the 4-way tip, TriDie Pressurized Dust was injected into each base void per label directions. (This same process was also used for all bath vanities.)
ELECTRIC OUTLETS. One of the projects was having an electrician switch out every outlet and light switch in the house, installing decorative rocker switches and matching outlets. After this was done and prior to installing new outlet and switch plates, I applied TriDie Bulk dust into the wall behind each outlet and switch box. The dust was applied using the cordless electric Exacticide Duster (by Technicide) to better push dust deeper into walls.
LIGHTS & CEILING FANS. Another project involved updating most of the light fixtures and ceiling fans in the house. After each fixture was removed, the space/void behind the fixture in the ceiling was treated with TriDie Bulk Dust. The new light fixtures and ceiling fans, once installed, fit tightly against the ceiling, which would prevent spiders and insects from exiting the ceiling/attic into the rooms below.
For the can lights in the house, the bulbs were removed, and dust applied through the can light housing ventilation holes into the area around the light in the ceiling void/attic. LED retrofit lights designed for can lights were then installed into each can light. These retrofits look nice and create a fairly tight fit against the ceiling, which helps close off access to spiders and other pests from entering the rooms below.
PLUMBING. Recluse spiders and other pests use plumbing lines and drain lines to move through walls and from the attic and substructure into living areas of buildings. At each site where a water line or drain line exited a wall under sinks, behind toilets and the laundry room, the wall void behind was treated with TriDie Bulk Dust applied using the Exacticide Duster. Following treatment, either silicone sealant or Xcluder Rodent Control Fill Fabric was used to seal off any gaps around water/drain lines to prevent recluse spiders from being able to exit walls in these sites.
BATH TRAPS. The bath trap space/void under each bathtub was accessed either by the bath trap’s access panel where present or by drilling a hole through the wall into the space. Treatment of TriDie Bulk Dust was applied using the Exacticide duster.
ATTIC. In the two attic areas, TriDie Bulk Dust was applied using the Exacticide duster to all cracks between joists, rafters, etc., that were safely accessible. Treatment with dust also was made along the sides and under insulation in as many areas as possible, especially where evidence of recluse spiders was noted. Some areas of the attic were not easily accessible but could be decently treated using the Exacticide duster’s extendable hose applicator. Where flooring was present in the attic, dust was applied into every available crack between floorboards.
TriDie Bulk Dust also was applied into all accessible soffit areas for general insect control. The exclusion efforts on the house detailed in the previous article hopefully limits the numbers of insects that can enter (those insects serve as a food source for recluses and other spiders).
Last, dust was applied lightly as spot treatments in between stored boxes and along sill plates and floor/wall junctures in the attic to help control spiders that crawl along these areas. Insect monitoring traps were placed along floor/wall junctures and other targeted areas. (Note: Wholesale “power dusting” or ULV treatment of an attic are generally not recommended. For recluse spiders, targeted applications with properly labeled residual products are typically better as these spiders are hiding in cracks and voids, not routinely crawling in the open on top of insulation.)
CRAWLSPACE. Most recluse spiders in a crawlspace are harboring in cracks between joists and sills and inside hollow blocks, brick or stone foundations. Treat such cracks using a dust insecticide. Treatment along sills and headers using a water-based residual, if desired, could be beneficial in some situations.
EXTERIOR. Night inspections revealed a few recluses foraging on the exterior brick walls, likely emerging from harborage through weep holes in the brick or from behind wood trim near the soffits. One day I witnessed a recluse emerge during broad daylight from behind trim on the outside and saw it capture a small wasp that had landed nearby. It was the first time I had witnessed a recluse spider performing its role as an ambush hunter (see photo).
Using the Exacticide duster, all weep holes in the brick siding were treated with TriDie Bulk Dust. The Exacticide’s extendable applicator tube was used to treat cracks around wood trim that were too high above ground to reach with a ladder. (Later, when the exclusion efforts was completed on the outside, these cracks were treated again with the dust and the cracks sealed using silicone sealant or Xcluder fill fabric, depending on the size of the gap to be filled.)
A perimeter treatment and general spider control treatment were completed using Fendona CS Controlled Release Insecticide (BASF Corp.). Applications were made to the perimeter foundation per label directions and also to corners and edges where web-building spiders typically locate webs. Such applications were repeated at two- to three-month intervals.
WATER-BASED APPLICATIONS. After all of these treatments were completed, fresh monitoring traps were placed for three to four weeks to gauge activity (this was at the beginning of summer). Although captures on traps and sightings of recluse spiders decreased quite a bit, regular sightings still occurred.
At this point, water-based applications indoors were conducted to determine how such treatments might further affect observed activity. Fendona CS mixed to interior label rates for spider control were applied as spot treatments to baseboard areas behind furniture, appliances throughout the house.
Following this application, the sightings of spiders dropped to zero for about one month and traps captured only a few spiders. After spider activity picked up again, another interior application of Fendona CS was applied and again, sightings dropped to zero for a number of weeks. To me, these observed results suggest that surface-applied spot treatments applied to sites where recluses are likely to walk, such as along walls behind furniture, may be an important component of brown recluse control.
PRODUCTS USED. I have long been a proponent of using residual dust products for control of brown recluse and most other pests that spend most of their time hiding in cracks and voids. My experience with products formulated of silica aerogel dust combined with pyrethrins has been excellent for most structural pests I have treated, including brown recluse spiders.
I thank BASF Professional & Specialty Solutions for supplying the products mentioned throughout this article and Technicide for providing the duster and its accessories.
SUMMARY. The approach described here is not exactly the one I might recommend for a customer afflicted with a brown recluse infestation. The products and treatment techniques are recommended, and I know from experience that the greater the numbers of recluses initially in a home, the more frequently one should complete follow-up services.
For example, the initial service may take many man-hours to complete, especially for a large to severe infestation. Monthly follow-up services in that case should be recommended for awhile. Such monthly follow-ups may include reapplication of residual dust to key sites (based on previous observations), application of spot treatments to baseboard areas behind furniture and replacement of traps that have captured spiders. Every situation is different so it is up to the pest company to determine what service interval might work best for a particular situation.
My goal after I purchased my home was to try different steps and then observe what changes in spider activity occurred following each task. Now that the remodeling and exclusion efforts are complete, next year I plan to conduct regular services/treatments to the house similar to those a pest professional might complete for a customer.
Total elimination of a brown recluse infestation is unlikely to occur in a house like mine that begins with a moderate number of recluse spiders. It is even more unlikely with severe infestations or those that involve an older home (30+ years old) or, in my experience, one with a wood shake roof. In the Mid-South area of West Tennessee where I live, most homes will, at one time, experience a brown recluse sighting, and many others have entrenched recluse populations. In the past I’ve told my customers that at best we should be able to get an infestation to the point where only an occasional recluse is seen or captured on a trap. Such is the goal with my own home.
The author is with Stoy Pest Consulting, Memphis, Tenn.