Subterranean termites are killed by chemical termiticides applied to soil, baiting systems that poison entire colonies from within, borate-treated wood, extreme heat, and physical barriers that block their access to structures. The most effective approach depends on whether you’re preventing an infestation or eliminating an active one, and most professionals combine two or more methods for reliable results.
Non-Repellent Liquid Termiticides
The most widely used professional treatment for subterranean termites is a liquid termiticide applied to the soil around and beneath a structure’s foundation. These chemicals fall into two categories: repellent and non-repellent. Non-repellent formulations are generally preferred for active infestations because termites can’t detect them. They walk through treated soil, pick up a lethal dose, and carry traces of the chemical back to nestmates before dying.
Fipronil is the dominant active ingredient in the U.S. termite control industry. It works as a slow-acting nerve poison, giving exposed termites time to return to the colony and spread the toxicant through grooming and contact. However, recent research from the Journal of Economic Entomology reveals an important limitation: termites that die near the treated zone create a “death zone” of contaminated corpses that surviving colony members learn to avoid. In laboratory colonies placed just 1.5 meters from a fipronil-treated zone, mortality ranged from 23% to 66%, and most of that killing happened within the first few days. Colonies placed farther away lost as little as 1.6% of their population. The takeaway is that liquid treatments work best as barriers rather than colony eliminators.
Other non-repellent active ingredients include imidacloprid, chlorfenapyr, and chlorantraniliprole. Each has a slightly different mechanism, but they share the core advantage: termites enter treated soil without detecting it, pick up the poison through contact and by forming soil into pellets with their mouthparts (oral exposure causes more mortality than skin contact alone for most termiticides), and die shortly after.
Why Repellent Termiticides Work Differently
Repellent termiticides, typically pyrethroids like permethrin and bifenthrin, take a different approach. Instead of killing termites that pass through, they create a chemical wall that termites actively avoid. Label directions instruct applicators to create an unbroken vertical or horizontal barrier around a structure. When that barrier is continuous, termites simply can’t get in.
The weakness is that repellent treatments don’t cause significant colony mortality. If there’s even a small gap in the treated zone, termites find it and exploit it. Because they’re driven away rather than killed, the colony remains fully intact and continues searching for entry points. For this reason, repellent products are considered better suited for preventative treatments on new construction, where a complete, unbroken barrier can be applied before the slab is poured. Non-repellent products are the stronger choice for remedial treatments on homes with existing infestations.
Baiting Systems That Eliminate Colonies
Baiting systems take longer but target what liquid treatments often miss: the colony itself. Plastic bait stations are installed in the ground around a structure, typically every 10 to 15 feet. Foraging termites discover the stations, feed on the bait, and carry it back to share with the rest of the colony.
The active ingredients in most commercial bait systems are chitin synthesis inhibitors. Termites have an exoskeleton made of chitin that they must shed and regrow as they develop. These compounds block that process, so when a termite tries to molt, it dies. Because termites share food through mouth-to-mouth feeding, a relatively small number of foragers can spread the toxicant throughout the colony, including to the queen.
Lab testing on Formosan subterranean termites showed that colonies of 2,500 individuals exposed to baits containing chitin synthesis inhibitors (including hexaflumuron and diflubenzuron) at 250 parts per million died completely within 9 weeks. Control colonies with untreated bait were still alive 6 months later. In real-world conditions, full colony elimination with baiting systems typically takes longer, sometimes 2 to 4 years for large subterranean colonies, because foragers must first locate the stations and the bait must spread through an underground population that can number in the hundreds of thousands or millions.
Borate Wood Treatments
Borate compounds, most commonly disodium octaborate tetrahydrate (DOT), kill termites that feed on treated wood. Boron disrupts their digestive system, effectively starving them. Commercial treatments use a 23% DOT solution brushed or sprayed onto lumber, and it’s most commonly applied during construction before walls are closed up.
The challenge with borates is penetration depth. In standard conditions, boron concentrates in just the outer 5 millimeters of wood regardless of how long you wait. That’s enough to kill termites feeding on the surface, but it doesn’t protect against deep boring. Higher humidity dramatically improves results. When treated wood is stored in humid conditions (around 20% equilibrium moisture content), boron penetration exceeds 5 mm after 6 weeks and reaches over 11 mm after 26 weeks, covering more than 70% of the wood’s cross section.
Borates are most effective as a preventative measure in new construction, particularly in crawl spaces and framing lumber. They’re water-soluble, so they aren’t suitable for wood exposed to rain or ground contact unless sealed with a topcoat.
Heat and Temperature Extremes
Subterranean termites are vulnerable to sustained high temperatures. Eastern subterranean termites reach 100% mortality after one week at 35°C (95°F). Formosan subterranean termites are hardier, surviving well between 15°C and 30°C with 88% to 94% survival, but they also reach complete mortality at 35°C if the exposure lasts 8 weeks.
Professional heat treatments pump hot air into infested wall voids and structural spaces, raising wood temperatures above lethal thresholds. This works best for drywood termites in accessible areas, but it’s less practical for subterranean species because their colony lives underground, well insulated from surface temperatures. You can kill the termites inside your walls with heat, but the colony beneath the soil survives and can reinvade.
Physical Barriers
Physical barriers don’t poison termites but prevent them from reaching a structure in the first place. Two types have strong research backing.
Basaltic particle barriers use crushed volcanic rock in a specific size range. Research at the University of Hawaii found that particles sized between 1.7 and 2.4 mm completely blocked Formosan subterranean termites from passing through, even when the barrier was left in place for five years. The particles are too heavy for termites to move and too tightly packed for them to squeeze between. These barriers are installed in trenches around foundations or beneath slabs during construction.
Stainless steel mesh works on the same principle. Mesh with an aperture of 0.66 by 0.45 mm is well below the 1.2 mm opening size that Formosan subterranean termites need to pass through. The mesh is installed over potential entry points like plumbing penetrations, expansion joints, and the junction between foundation walls and slabs. It’s corrosion-resistant and lasts the life of the structure.
Essential Oils and Botanical Options
Several plant-derived oils show genuine toxicity against subterranean termites in laboratory settings. Clove bud oil is the most potent tested, killing 100% of Formosan subterranean termites within 2 days at a concentration of 50 micrograms per square centimeter. Vetiver oil stops tunneling activity at concentrations as low as 5 micrograms per gram of sand, and at 25 micrograms per gram, termites won’t tunnel or feed at all.
These results are promising but come with a significant caveat: they’re from controlled lab environments with small termite groups and measured doses. Essential oils break down quickly in soil and lack the long residual life of synthetic termiticides. They may have a role as localized deterrents or in combination with other methods, but no essential oil product is currently registered or proven as a standalone treatment for an active subterranean termite infestation in a home.
Combining Methods for Best Results
No single method is perfectly reliable on its own against subterranean termites. Liquid soil treatments create a protective zone but may not eliminate the colony. Baiting systems can destroy entire colonies but take months or years to work. Physical barriers block entry but don’t address termites already inside. The most effective professional programs pair a liquid barrier treatment with a baiting system: the barrier provides immediate protection while the bait works to collapse the colony over time. Adding borate-treated lumber during construction or renovation gives a third layer of defense at the wood itself.