Odorous House Ants: How to Identify Them and Get Rid of Them for Good

TL;DR

• Odorous house ants are small brown to black ants that give off a rotten coconut smell when crushed. To check, crush one on a paper towel and sniff.
• Pavement ants look similar, but they have two clearly visible nodes on the waist and do not smell when crushed.
• Don't spray. Spraying along trails may split the colony into new nests (Health Canada).
• Use a sweet, slow-acting bait that workers carry back to every nest and queen. Put it directly on each active trail you can find.
• Leave baits out for at least two weeks and replace them as they empty. Seeing more ants in the first days is normal.
• Need help? Get a quote from a recommended local exterminator through Pest Agent's referral form.

Odorous house ants are often the trail on the kitchen counter that seems to grow every time it gets sprayed. Small, dark and easy to mistake for any other household ant, they answer a poorly aimed insecticide by splitting: a queen and a group of workers carry the brood off and start a new nest somewhere else in the house.

That habit makes identification the first real step, before any product comes out of the cupboard. Crushing a single worker settles most of the question, since this species gives off a smell its closest look-alike lacks.

What Are Odorous House Ants?

Odorous house ants (Tapinoma sessile) are small brown to black ants, native to North America, that give off a rotten coconut smell when crushed. They nest outdoors under stones, wood and mulch, and they move indoors into wall voids and damp spots near pipes. Health Canada lists the odorous house ant among the ants that commonly invade Canadian homes, alongside carpenter ants, little black ants, thief ants and pharaoh ants. For an overview of every species, start with our ant guide.

What Does an Odorous House Ant Look Like?

An odorous house ant worker is about 2.4 to 3.3 mm (about 1/10 to 1/8 inch) long, uniform brown to black, and every worker in a colony is about the same size (Penn State Extension). Its antennae have 12 segments with no club at the tip. The waist has a single node that is hidden under the abdomen, so from above the ant seems to have no waist bump at all. When disturbed, workers run in an erratic, zigzag way with the abdomen raised in the air (UC IPM).

Why Do Odorous House Ants Smell Like Rotten Coconut?

Odorous house ants smell like rotten coconut because crushed workers release a strong odour, which is how the species got its name. Some people compare it to blue cheese (University of Wisconsin Extension), and pest control companies also call them stink ants or coconut ants. The smell test is the easiest way to confirm the species at home: crush one ant on a paper towel and sniff.

How Are Odorous House Ants Different From Pavement Ants?

Odorous house ants differ from pavement ants mainly in the waist and the smell. According to Utah State University Extension, pavement ants have a similar colour and size but two clearly visible nodes on the waist, and they do not smell when crushed. Odorous house ants have one hidden node and the rotten coconut odour.

Many people also call odorous house ants "sugar ants", a loose name for several small ants that go after sweets. If you are not sure which ant you have, our guides to small ants in the house and getting rid of sugar ants cover the other common species.

Where Do Odorous House Ants Live in Canada?

Odorous house ants live across much of Canada. The Government of the Northwest Territories species profile records them in Yukon, British Columbia, Alberta, Manitoba, Ontario and Quebec, and expects them in the other provinces and territories too. In Alberta, they are found province-wide. Unlike tropical indoor ants, they are a native species that survives Canadian winters outdoors, so colonies around your yard are normal.

How Does an Odorous House Ant Colony Spread?

An odorous house ant colony spreads by budding. Each colony has many queens and usually several thousand workers (Penn State Extension), and colonies in urban areas can reach tens of thousands of workers (Utah State University Extension). Nests are linked in a network, and a queen can leave with a group of workers and brood to start a new nest nearby. Disturbance, including incomplete insecticide treatments, encourages this split. That is why killing the ants you see rarely ends the problem.

Are Odorous House Ants Dangerous?

Odorous house ants are not dangerous to people. Utah State University Extension notes they do not bite unless provoked and cannot sting. The real issue is food: their feeding can contaminate stored pantry items (Penn State Extension), so throw out any open food they have reached.

Why Do Odorous House Ants Come Inside?

Odorous house ants come inside looking for sweets and moisture, most often after rain or when outdoor colonies become active again in spring. Knowing what draws them helps you find their trails and nests.

Sweet Food

Sweet food is their first target. Odorous house ants prefer sugary foods, and outdoors they feed on honeydew, the sugary waste of aphids and scale insects (Penn State Extension). They also eat dead insects, grease and occasionally pet food, but Utah State University Extension notes they do not like fat-based foods. This matters when you pick a bait.

Rain

Rain is a common trigger. According to UC IPM, odorous house ants are most likely to invade homes during rainy weather, because rain washes their honeydew food off plants. A sudden trail across the kitchen counter after a wet week is classic odorous house ant behaviour.

Moisture and Warmth

Moisture and warmth decide where they nest inside. Odorous house ants prefer wall voids with heated pipes, areas near leaks and condensation, damp wood and insulation, and spots around sinks, bathtubs and toilets (Utah State University Extension, Penn State Extension). If ants keep appearing from the same outlet or baseboard, the nest may be inside the wall; our guide to ants in walls explains how to track it down.

Overwintering Nests

Overwintering nests explain the spring surge. In winter, odorous house ants gather in a few nests; in spring these nests bud, and by summer many nests are present again (Utah State University Extension). Outdoor colonies resume foraging as temperatures warm in March, and nests inside a heated home can stay active all year (UC IPM). Winged ants may appear from May through July (Penn State Extension).

Ant Trails

Ant trails show where they come from. Odorous house ants forage day and night along set paths: baseboards, carpet edges, door frames, siding and foundations (UC IPM, University of Wisconsin Extension). Utah State University Extension reports trails often 33 to 157 feet (about 10 to 48 metres) long, so the nest feeding your kitchen may be outside, under mulch or a patio stone. Follow a trail to see where it enters the house.

How Do You Get Rid of Odorous House Ants?

Getting rid of odorous house ants takes a sweet, slow-acting bait that workers carry back to every nest and queen, not a spray. For a broader method that covers every species, see how to get rid of ants.

Why Sprays Make Odorous House Ants Worse

Sprays make odorous house ants worse because they can split the colony. Health Canada warns that spraying indoors along trails may split a colony, and the City of Calgary notes that some barrier spraying may cause the colony to bud. Utah State University Extension adds that repellent treatments that cut a trail can create new problems indoors, because ants cut off from their nest set up new ones. Health Canada also states that you should not use chemical sprays while using a bait system, or the bait will not work.

Sweet Baits

Sweet baits are the most reliable way to get rid of odorous house ants. Worker ants drink the bait, carry it back to the nest and share it with the queens and young. Penn State Extension recommends baits designed for sweet-loving ants, and the University of Wisconsin Extension says sugar-based baits work well for nests you cannot reach, such as wall voids. Liquid bait stations and gel baits are the usual formats. For tested products, see our picks for the best ant killer.

Bait Placement

Bait placement decides whether the bait reaches every nest. Put bait stations or small dots of gel directly on active trails, next to baseboards, counters and windowsills where you see ants. Odorous house ants live in connected nests, so Utah State University Extension advises finding as many trails as possible and baiting along each one. Keep baits out of reach of children and pets (Health Canada), and do not wipe the trails or spray near the bait.

How Long Baiting Takes

Baiting odorous house ants takes at least two weeks. Health Canada advises leaving baits out for at least two weeks and expecting to reapply, and Penn State Extension says control may take two weeks or longer. Do not panic if you see more ants in the first days: the University of Wisconsin Extension notes that activity may increase as more workers are recruited to the bait. Replace baits as they empty until no ants show up.

Bait Active Ingredients

Bait active ingredients that work on odorous house ants include boric acid and fipronil, which act slowly so workers can share them before dying (Penn State Extension). Borax liquid baits and indoxacarb gels are also labelled for odorous house ants in the United States. Before you buy in Canada, check that the label lists ants for indoor use and shows a Pest Control Products (PCP) number, which Health Canada says confirms the product is registered for use here. If you have pets, read our guide to pet-safe ant killers.

Homemade Borax Bait

Borax baits can work on odorous house ants because they love sugar, but Health Canada advises Canadians not to make homemade pesticides using boric acid, and borax can produce boric acid. Use a registered borate bait station or gel instead, placed on the trails away from children and pets. Our guides on using borax to kill ants and homemade ant killers explain the risks of homemade bait.

Outdoor Nests

Outdoor nests can be treated directly once you find them. The University of Wisconsin Extension suggests a product labelled for ants on exposed outdoor nests, but warns that because nests are interconnected, one treatment may not solve the problem. Utah State University Extension notes that nests in mulch can be exposed by raking the mulch back before treating, and that you should check again for new nests afterwards. Keep using baits indoors while you deal with outdoor nests.

When to Call a Pest Control Professional

Calling a pest control professional makes sense when ants keep coming back after several weeks of careful baiting, when trails lead into walls or under a concrete slab, or when the infestation is large. The University of Wisconsin Extension recommends hiring a professional for extensive infestations, and Utah State University Extension notes that nests under slabs or in wall voids may need treatments only licensed applicators can do. A typical professional visit includes species identification, an inspection of trails and moisture sources, gel or granular baits, non-repellent treatments and advice on sealing entry points. If you want help, you can get a quote from a recommended local exterminator through Pest Agent's referral form.

How Do You Prevent Odorous House Ants From Coming Back?

Preventing odorous house ants means taking away the sugar, water and shelter that draw them in, then closing the gaps they use. These habits also make baits work better, because the bait becomes the easiest food around.

Food Storage

Food storage is the first line of defence. Health Canada suggests storing ant-attractive foods in glass jars with rubber gaskets or plastic containers with snap-tight lids, keeping counters clean and emptying the kitchen garbage often. Sweep or vacuum often, especially around pet dishes, and rinse containers before putting them in the recycling bin (City of Calgary). Health Canada also suggests setting pet food dishes in a shallow dish of water, since ants cannot swim across it.

Moisture Control

Moisture control removes what odorous house ants need most. Fix leaking pipes, toilets and sinks, clean out leaking gutters and make sure sprinklers do not soak the foundation (Utah State University Extension). Wipe up condensation around windows and under sinks.

Mulch and Plants

Mulch and plants against the foundation give odorous house ants shelter and a bridge into your home. Keep plants and debris piles at least a foot (about 30 cm) from the house, prune shrubs and branches touching the walls, and consider replacing wood mulch next to the foundation with pea gravel (Utah State University Extension). Controlling aphids on nearby shrubs also cuts their honeydew supply.

Sealing Entry Points

Sealing entry points closes the paths odorous house ants use. Caulk cracks in the foundation and walls, gaps under sliding doors and around window frames, and openings where pipes and utility lines enter (Utah State University Extension, City of Calgary). Do it once baiting has worked, so you do not cut trails and push the colony into new nests while the bait is still being shared.