Carpenter Ants. How to Find the Nest and Stop the Damage

Carpenter ants (genus Camponotus) are the largest ants in Ohio homes. The black carpenter ant is Ohio's most common species. Minor workers are about 1/4 inch and major workers about 1/2 inch. Size alone is not reliable, because one colony has workers of several sizes.¹

In California, Camponotus modoc and C. vicinus are the most destructive. Workers run 1/4 to 1/2 inch. The smaller yellow and black C. clarithorax is also common.²

Ants have a pinched waist and elbowed antennae. Termites do not.³ Ohio field ants (Formica) look alike but build soil mounds, and their control is different.¹ Back to the ant hub.

The parent nest holds the queen. It sits in damp, decayed wood, often hardwood, with moisture above 15 percent.¹ Satellite nests are in drier, warmer areas. Inside homes they turn up in hollow porch posts, crawl spaces, hollow doors, curtain rods and under attic insulation.¹

Indoor nests are typically satellites of a parent nest outside, such as a tree, woodpile or landscaping timber.² A nest can hold several thousand ants.²

Winged swarmers emerge from mature colonies from March to July in Ohio. Eggs laid in spring produce sexual forms in August and September.¹

• Frass that looks like pencil sharpener shavings, often in piles under nest openings called windows. It can include insect parts and seed husks.¹
• A dry rustling like cellophane in a wall.¹
• Large ants moving on trails at night.¹
• Smooth, clean galleries with no soil.¹
• Trails from a tree cavity or stump to the house.¹

UC IPM says to inspect after sunset, when carpenter ants are most active, and follow the trail back to the nest.² Their sawdust is fibrous, unlike the six-sided pellets of drywood termites.²

Carpenter ants do not eat wood. They excavate it to enlarge nests.³ The damage is slower than termite damage, but colonies often start where water or decay already hurt the wood, and they can expand into sound wood.²

That is why moisture is the first thing to check. Roof leaks, bad gutters, skylights and chimneys are common starting points.¹

The sources we used list no disease threat from carpenter ants. Indoor bait stations must be childproof.¹

The goal is the queen. Find the parent and satellite nests, since the colony only ends when the queen dies.¹ Spraying around the ants without hitting nests is generally ineffective.¹

Ohio State lists these tools. Vacuum nests or treat them with insecticide. Use dust through drill holes about three to six feet on either side of the entry site for wall voids. Use aerosols where there is a lot of insulation.¹ Baits work on their own when placed on or near trails and entrances.¹

UC IPM says to use slow-acting baits, and offer a nontoxic food such as sugar milk first to see what the ants take.² Perimeter sprays go on the foundation 2 feet up and 3 feet out, and need a summer reapplication every four to six weeks.¹ Ohio State says many ant jobs are best handled by licensed pros, which fits a nest inside a wall.³

Fixr lists carpenter ant removal near $250 for a 1,000 square foot home. A big job with treatment and repairs on a house over 3,000 square feet can reach $1,200.⁴

General ant treatment runs $200 to $300. Poison bait runs $120 to $200 and barrier sprays $80 to $120.⁴ Carpenter ants usually need more than a barrier spray. Ask the pro whether the quote includes finding the nest and a follow-up visit.

• Fix moisture problems such as leaks, poor ventilation and blocked gutters.¹
• Replace rotted wood and end wood-to-soil contact.¹
• Remove dead stumps within about 50 feet of the house if practical.¹
• Prune broken limbs and trim branches that touch the house.¹
• Store firewood off the ground and away from the house.¹
• Seal foundation cracks, especially where pipes and wiring enter.¹
• Keep mulch 2 to 3 inches deep or less near the foundation.²

In Ohio, swarmers emerge from March to July, and workers forage mainly at night.¹ In California, mating flights are in spring, and Camponotus modoc swarms in the late afternoon, often after heavy rain.²

Inspect at dusk. Spring is when you will see the winged ones.

The black carpenter ant, Camponotus pennsylvanicus, is the most common Ohio species.¹ Perimeter sprays are reapplied every four to six weeks in summer, or within a week after heavy rain.¹

Treatment by a company needs an Ohio Department of Agriculture commercial applicator license. Category 10a covers general pest control.⁵ Back to the ant hub.

Camponotus modoc and C. vicinus are the two most destructive Western species and are found in California.² C. vicinus nests can have up to 40 queens.²

UC IPM lists pyrethroid sprays and borate dusts as effective. Desiccant dusts such as silica gel need a licensed applicator, and so do perimeter sprays with fipronil.² California pest companies are licensed by the Structural Pest Control Board.⁶