Ant Control & Prevention

Common Ant Species in St. Louis

Ants are the most common household pest in the St. Louis metro area. Missouri’s warm, humid summers and mild winters create ideal conditions for large ant colonies to establish themselves in yards, foundations, and wall voids. A trail of ants across your kitchen counter signals a colony that could number in the tens of thousands, foraging from a nest inside your walls or just outside your foundation.

Odorous House Ants

The most frequent invader in St. Louis homes. Small (1/8 inch), dark brown to black, they emit a rotten coconut smell when crushed. Colonies can have multiple queens and hundreds of thousands of workers, making them extremely persistent. They nest in wall voids, under slabs, and in mulch beds.

Carpenter Ants

Missouri’s largest ant species (up to 1/2 inch). Black or dark red, they excavate galleries in water-damaged or softened wood. Unlike termites, they do not eat wood — they remove it to create nesting space. Sawdust piles (frass) near baseboards or window frames are a telltale sign.

Pavement Ants

Small, dark brown ants that nest under sidewalks, driveways, and foundation slabs. You will often see small mounds of displaced soil along expansion joints and cracks. They forage indoors along plumbing lines and slab edges.

Pharaoh Ants

Tiny (1/16 inch), yellow to light brown ants that are notoriously difficult to control. Standard repellent sprays cause colony budding — the colony splits into multiple new colonies, making the problem worse. Pharaoh ants require specific bait protocols.

Signs of an Ant Problem

• Ant trails along baseboards, countertops, window sills, or door frames
• Fine sawdust (frass) near wood structures — indicates carpenter ants
• Soil mounds along sidewalks, driveways, or foundation cracks
• Ants emerging from wall outlets, light switches, or plumbing penetrations
• Persistent activity that returns within days of using store-bought sprays
• Winged swarmers appearing indoors, especially in spring

How Roberts Treats Ants

Roberts uses a targeted, multi-product approach to ant control. For active infestations, we apply a non-repellent perimeter treatment around the foundation. This non-repellent chemistry means ants walk through it unknowingly and carry it back to the colony, creating a transfer effect that eliminates the entire nest — not just the ants you can see.

Inside, we use professional-grade residual spray along baseboards and entry points, combined with gel bait placed near active trails and foraging areas. The gel bait is carried back to the colony and shared through trophallaxis (food sharing), killing the queen and collapsing the colony from within.

For carpenter ants, we add void treatment — injecting product directly into wall voids and galleries where the colony nests. For pharaoh ants, we use specific bait formulations designed to avoid colony budding.

Ant control is included in our R.O.S. (Regular Outside Service) program, which uses a 3-chemical rotation system to keep ants and other crawling pests out year-round. Learn more about R.O.S. →

Prevention Tips

• Eliminate moisture — Fix leaky pipes, poor drainage, and condensation. Carpenter ants are especially attracted to water-damaged wood.
• Seal entry points — Caulk cracks around your foundation, windows, doors, and where utility lines enter.
• Clean food sources — Store food in sealed containers, clean up crumbs promptly, and don’t leave pet food out overnight.
• Manage landscaping — Keep mulch 12+ inches from the foundation. Trim branches and shrubs away from the house.
• Move firewood — Store firewood at least 20 feet from the house, elevated off the ground.
• Address moisture in crawl spaces — Ensure proper ventilation and consider encapsulation for persistently damp areas.