They’re small, they’re smelly, they’re conga-lining straight to your sugar and they’re bringing thousands of friends with them.
Behold, the tiny-but-mighty odorous house ant.
Known by many names — Tapinoma sessile, sugar ant, “a darn nuisance” — odorous house ants are likely the tiny insects that residents encounter when they see a newfound ant party atop a discarded piece of fruit or in a multiple-feet-long line. They thrive and show up en masse in urban areas.
This spring, they’re invading the Seattle area in full force.
“This time of year, we have all the conditions that are perfect: weather, moisture, everything they like,” said Luke Rambo, president of Rambo Total Pest Control. “They are busy, and are active and looking to expand their territories.”
Odorous house ants have become among the leading ant pest in the Pacific Northwest over the past 10 to 15 years, experts say, as multiqueen super colonies expand and become increasingly attracted to living alongside humans. Unlike other ants such as their carpenter counterparts, odorous house ants aren’t destructive, but as anyone who finds them swarming in a flowerpot, or flour bag, knows, they’re a nuisance.
And for any ants found marching one by one (hurrah, hurrah) across a countertop or deck stairs, hundreds of thousands are lurking elsewhere.
In natural environments like forests, colonies can be small, with one queen and hundreds of worker ants, according to Sam Dilday, a recent master’s graduate from Washington State University’s department of entomology whose research focus is odorous house ants. (Her original focus was honeybees, but she said she got tired of being stung so much she shifted to ants. They’re nicer.)
But in urban areas, there are humans providing both food sources and threats, along with environmental pressures like competition from other pests. So we get polydomous (multinest), polygynous (multiqueen) supercolonies with thousands of queens and hundreds of thousands of workers. A Seattle neighborhood can be the site of a minuscule ant HOA whose colonies share resources as they take over, city block by city block.
Even when they number in the hundreds of thousands, these odorous house ants have a unique, well-defined social structure. Within the colony, each individual ant has its own job. The foraging ants, the pantry- or bathroom-sink-invaders, represent about 10% of the population and bring the nutrition and moisture to the other 90% so they can survive.
The queens are the reproductive royalty who get fed and tended to by the worker ants. Once a colony has matured enough, winged males — whose sole purpose is to provide genetic material, so they die quickly — and females will reproduce and, in a process called budding, the females will move to a different location to start a new colony. The process from egg to worker ant can take up to 11 weeks, according to Dilday, and as many as five generations can be produced within one year in a colony.
An ant census published in 2022 estimated there are 20 quadrillion ants around the globe — and that’s a conservative estimate, according to the report published in the Proceedings of the National Academy of Sciences. With 8 billion people on Earth, that’s about 2.5 million ants per person.
Ants, for their part, are important to the ecosystem. They act as decomposers and feed off dead animals, help aerate soils, and spread materials like seeds.
“I know they can be a pest, but there is a lot we can learn from them,” Dilday said. “But if they are in your home, I get that.”
And one annoyance comes from the reason they’re called odorous house ants — they produce an odor from their anal glands that, when the ant is crushed, smells of rotten coconut, or blue cheese, or any variety of unsettling olfactory experience.
Odorous house ants are harder to get rid of than other types of ants, pest control experts say. They’re nomadic and social, so they get along with different colonies. They like to move often, around every 21 days.
“Whenever they find a rich resource, it influences them to go, ‘Oh, let’s try to save energy by moving the whole family instead of going back and forth, back and forth,’ ” Dilday said.
When other types are killed by chemicals or fight to the death, the odorous house ants make themselves at home in the loser’s nests.
“They are survivors, and they are tough,” Rambo said.
Ants are active year-round, though they slow down significantly in winters in a dormant stage called diapause. Spring brings moisture, warmth and food sources, like aphids that feed on plant sap. Ants are attracted to honeydew, the sweet secretion produced by aphids.
This previous winter was mild, so more ants survived and are now growing in population size and demand to feed their colonies, said Matt Mendelsohn, president of Eastside Exterminators.
Ants are the No. 2 complaint, after rodents, at Eastside Exterminators, and each call brings a slightly different mystery. Mendelsohn remembers one call to a Redmond home. The complaint: ants in the kitchen. The evidence: an ant trail from the back door to the cabinet and counter, and the remains of old fruit. He treated the outside of the house and thought he had solved the cut-and-dried case.
But a week or two later, the ants were back, and this time in a slightly different location. Mendelsohn followed the trail and discovered there were multiple colonies. One was in the interior of the home’s drywall, which required the technicians to make small holes to get the product behind the wall. Another trail led them to a shed, and a colony of thousands and thousands of ants.
Mendelsohn pieced together what had happened. The homeowners had used an insecticide, which killed some ants on contact but repelled the others and split up the colony, so they created satellite colonies in different spots.
“It’s important for us as pest-control providers to know if they are using” insecticides, Mendelsohn said. “It could have adverse effects if it’s driving the ants all over the place instead of quarantining them in one location.”
Slow-acting baits are useful to eliminate the infestation but require patience. Taking out the foragers won’t help if the queens remain, because “the queen is the colony,” Dilday said. The worker ants will then take the bait and bring it back to the brood and queen, to then spread throughout the colony. That process can take weeks, depending on the size of the infestation.
The easier option is preventing the infestations in the first place by maintaining a buffer between nature and home. Experts recommend cutting shrubs or branches close to the home so they don’t become onramps to an ant highway. Kitchen debris or exposed pet food attract ants, as do damp environments in spots like gutters and downspouts.
If you do see an ant trail, clean the area with a soapy water to remove the trail pheromone, Dilday said. But if the ants keep returning or seem to be growing in number, it’s likely best to call a pest-control company, she added. They understand ant behavior and know which treatments to use that are safe for humans and pets.
“If you don’t want roommates,” she said, “ you might want to seek out professional help.”
