Pest of the month:

Oderous House Ants

In the Portland–Metro area, March is when we begin seeing the first wave of odorous house ants becoming active. While it’s still cold outside, these ants are already preparing for spring. As temperatures slowly rise and we get breaks in the rain, colonies start expanding and foraging inside homes and businesses.

If you’ve noticed small brown or black ants in your kitchen during late winter — March is typically when they begin showing up.

Odorous house ants are small (about 1/8 inch long), dark brown to black ants. When crushed, they give off a distinct “rotten coconut” or vinigry smell — which is how they got their name.

They are one of the most common nuisance ants in the Portland, Canby, Beaverton, Hillsboro, Tigard, Oregon City, and Salem areas.

Life Cycle of Odorous House Ants

Understanding their life cycle helps explain why February activity increases.

1. Egg Stage
The queen lays eggs in hidden nesting areas — often inside wall voids, insulation, or under floors during winter.

2. Larvae Stage
Larvae are fed by worker ants and develop rapidly when temperatures warm.

3. Pupa Stage
They transition into pupae before emerging as adult workers.

4. Adult Stage
Workers begin foraging for food once colonies need to expand. In late winter, colonies may split (a process called budding), creating multiple satellite colonies — which is why DIY sprays often make the problem worse.

In Oregon’s mild winter climate, colonies do not completely go dormant. Instead, they slow down and then ramp up again in February as days get slightly longer and warmer.

🏡 Habits & Favorite Conditions in Portland, Oregon

March in Portland means:

• Cool temperatures

• Heavy moisture

• Saturated soil

• Homes sealed tight for warmth

These ants love:

✔ Moisture (leaky pipes, condensation, damp crawlspaces)

✔ Wall voids and insulation

✔ Under sinks and around dishwashers

✔ Pet food bowls

✔ Sugar sources (syrup, soda, honey)

✔ Heated interiors during rainy spells

When the ground becomes too wet from winter rain, ants often move upward into structures to escape saturated soil.

🚫 What Homeowners Can Do to Prevent Ant Activity

Here are proactive steps Portland-area homeowners can take in March:

Seal Entry Points

• Caulk cracks around windows and doors
• Seal foundation gaps
• Repair torn screens

Reduce Moisture

• Fix plumbing leaks
• Use dehumidifiers in crawlspaces
• Ensure proper drainage away from foundation

Eliminate Food Sources

• Wipe counters daily
• Store food in airtight containers
• Clean pet bowls after feeding

Avoid Over-the-Counter Sprays:
Repellent sprays scatter colonies and cause budding — leading to more nests inside walls!