Ants inside walls are almost always a sign of either carpenter ants (moisture damage) or pavement/odorous house ants (colony inside the wall void). The two situations require completely different approaches.
📋 Steps
1
Determine which ant is in your wall
Carpenter ants: large (6-12mm), black or red-black, coarse sawdust pushed from wall openings, indicate moisture damage. Odorous/pavement ants: small (2-3mm), following scent trails from wall void to food. This distinction completely determines treatment.
2
For small ants in walls: do not spray — use bait
Small ants in walls respond to gel bait. Place small dots of Advion gel or Maxforce Quantum at the point where ants exit the wall (typically at baseboard gaps or outlet plates). The ants carry bait back to the colony inside the wall. Spraying repellents at this point causes ants to retreat deeper and scatter to new locations.
3
For carpenter ants: inject Delta Dust into the void
Access the carpenter ant void by removing the outlet plate on the wall where activity is concentrated. Use a bellows duster to inject Delta Dust into the void — 2-3 puffs. This treats the moisture-damaged wood where the colony is excavating. Also apply bifenthrin perimeter spray exterior.
4
Investigate the moisture source for carpenter ants
Carpenter ants in walls always indicate moisture-damaged wood. Find the water source: leaking pipe, window flashing failure, roof leak, condensation issue. Eliminate the moisture — the ants will eventually abandon a treated, dry void.
5
Follow up with exterior perimeter treatment
For any ant species in walls, a bifenthrin perimeter spray along the foundation intercepts ants entering from outdoors. Apply 3 feet up the wall and 3 feet out on the ground. Repeat every 60-90 days during active season.
💡 Tips
If ants are exiting from electrical outlet or switch plates on interior walls — this confirms a colony established in that wall void
Resist the urge to open the wall — treatment through outlets with Delta Dust is usually sufficient and avoids expensive drywall repairs
For carpenter ants, the presence of coarse sawdust (frass) pushed from holes or cracks confirms active excavation — this frass is how you find the nest location
Ant repellent sprays on interior walls cause colony dispersal into new voids — making the problem harder to find and treat
⚖️ Educational use only. Always follow product labels. Disclaimer →
💰 Cost to Fix This Problem
Approach
Typical Cost
Best For
DIY materials only
$15–$40
Mild or early-stage infestations
Professional service (one-time)
$130–$300
Active infestations or when DIY has already failed
Ongoing service contract
$400–$800/yr
Prevention and long-term peace of mind
Costs vary by region, property size, and severity. Get at least two quotes before hiring.
✅ How to Know It's Working
Pest control success is measured in weeks, not days. Here's what to look for:
Week 1–2: You may see increased activity as pests are flushed from hiding. This is normal.
Week 2–4: Activity should drop noticeably. Bait traps or sticky monitors should show declining counts.
Week 4–6: New activity near zero. Any resurgence means a population was missed or re-introduction occurred.
💡 Monitoring tip: Place sticky traps in corners and along walls before you start treatment. Counting catches weekly gives you objective data on whether the population is declining.
👷 When to Call a Professional
DIY is appropriate for small, contained infestations caught early. Call a licensed professional when:
You've tried DIY twice with no lasting improvement
The infestation involves a wall void, crawlspace, or area you can't safely access
There's a health risk involved (hantavirus, anaphylaxis risk, etc.)
The problem covers more than one room or a large outdoor area
You have children, elderly, or immunocompromised individuals in the household
⚠️ Rule of thumb: If you've spent more on DIY materials than a professional visit would cost, it's time to call.
❓ Frequently Asked Questions
How long does it take to eliminate ants nesting inside walls?
Wall-nesting ant colonies typically require 3-6 weeks of sustained bait treatment. CimeXa dust injected through outlet plates provides long-term control in wall voids and remains effective for up to 10 years in undisturbed spaces.
Should I drill into walls to treat ants?
Drilling is usually unnecessary. Electrical outlet plates provide direct access to wall voids. Remove the cover plate and puff CimeXa or boric acid dust inside with a bellows duster. This reaches the same cavity spaces without creating holes that need repair.
How can I tell if ants in my walls are carpenter ants?
Carpenter ants are the largest common household ant (1/4 to 1/2 inch), usually black or red-and-black. Look for small piles of sawdust-like frass near baseboards, and listen for faint rustling sounds in walls at night. Unlike termites, carpenter ants do not eat wood.
Will ants in walls cause structural damage?
Only carpenter ants cause structural damage by excavating nesting galleries in wood. Odorous house ants, pavement ants, and most other species nest in wall voids without damaging the structure. However, any ant colony in walls indicates moisture conditions worth investigating.