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You don’t want to bring these ants home from vacation
Pharaoh ants are not like other ants. And that is precisely the problem when they show up in your home.
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Pharaoh ants are very small and light in colour. You can see them, but they quickly disappear into a crack in the wall or under a shirt collar in your closet.
They can establish a colony anywhere indoors.
"Pharaoh ants have a very unusual biology compared with ants that live in Norway," says Anders Aak. He researches pests at the Norwegian Institute of Public Health.
Social but different
In many ways, they are like other ants: Pharaoh ants are social insects that live in colonies with a queen at the top. She produces workers that go out and fetch food for the rest of the colony, just as in an ordinary anthill.
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While other ants spread through large, conspicuous swarms, in which they develop wings and fly off to establish a new nest, pharaoh ants do things differently.
"When a colony becomes large enough, it splits in two. We call this budding. Half of the ants move to a new location and establish themselves there," says Aak.
They scatter in panic
This method of spreading makes pharaoh ants particularly difficult to get rid of. And if you disturb them, they spread even more.
“If they’ve settled in, say, a light switch and you remove the cover, they scatter in panic and settle in new places. So instead of just one colony, you suddenly have many,” says Aak.
Pharaoh ants are tropical insects that require warmth and high humidity. This means they cannot survive the Norwegian outdoor climate, but they thrive indoors, particularly in wet rooms or behind the stove.
“They spread internationally primarily through trade and tourism,” says Aak.
May end up in your TV
A typical scenario might play out in a warehouse in a tropical region where pharaoh ants are natural inhabitants. When an order bound for Norway is packed and loaded onto a pallet, the ants hitch a ride. Upon arrival, they crawl out of the pallet and establish themselves in the local warehouse.
“Then they might end up in the home of someone who bought a TV from that warehouse,” says Aak.
You can also pick them up in your luggage while staying at hotels abroad. They might be hiding in the folds of the bedsheets or in the bathroom.
Cannot tolerate cold weather
Aak once experienced ants moving into his suitcase while in Thailand. He had bought new shirts with collars stiffened using sugar. That was a tasty snack for the ants.
“In my case, they weren't pharaoh ants, but the same principle applies. If they find a good food source somewhere, they’re likely to settle there,” says Aak.
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If you suspect you have brought pharaoh ants home with you and the weather is cold, you can simply leave your suitcase outside.
"Pharaoh ants start having problems at temperatures as high as 10-12 degrees Celsius and will die outdoors in this country," says Aak.
They eat everything – which makes them a health hazard
Pharaoh ants are known as a tramp species.
"That’s an apt description, as they wander all over the world and settle wherever they find food and favourable conditions," says Aak.
Their eating habits also distinguish them from the ants commonly found in Norway.
"Carpenter ants and black garden ants also live in our homes, and they can damage woodwork and insulation. But they go outside to feed," says Aak.
Pharaoh ants eat whatever food they can find inside the house. This also makes them a health hazard.
"Imagine that one feeds on an old piece of raw chicken that you’ve thrown in the trash. Then it wanders over to the food sitting on your counter. That’s how it can spread salmonella, for example," says Aak.
People can also have both allergic and asthmatic reactions to pharaoh ants.
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They spread rapidly
In Norway, the number of pharaoh ant extermination cases has ranged between 30 and 50, with a peak of 85 in 2019. The pandemic, and the resulting reduction in travel, caused the numbers to drop again, as it did for other pests.
Although there are relatively few infestations, each one can be very extensive.
"They spread so rapidly from apartment to apartment. That's why they have to be exterminated throughout the entire building at the same time," says Aak.
Ant spray does not work.
"If you spray a colony of pharaoh ants, they will scatter, and you will have spread the problem instead of solving it," the researcher says.
Aak adds that Norway has a competent pest control industry. And they need to be brought in if pharaoh ants have entered your home.
Getting rid of pharaoh ants is expensive
Ragna Byrkjeland is a biologist and technical manager at Vis Insurance. Many of the pharaoh ant infestations are reported to them.
"We handle between 15 and 40 cases a year, but a single case can involve 100 apartments, all of which have to be treated," she says.
This is known as building-wide treatment, and it is expensive.
"A treatment can cost up to NOK 200,000 (20,700 USD). If you are insured, we cover the costs, subject to a deductible," says Byrkjeland.
But it doesn't have to cost that much – if you report it early.
"Typically, we receive a call or a claim from a customer stating they have lots of tiny ants in their apartment. We ask them which floor they live on. If it’s the fourth floor, it’s almost certainly pharaoh ants. Other ants don't settle that high up," says Byrkjeland.
Poison is necessary
Once it has been confirmed that the problem is pharaoh ants, treatment begins.
"Technicians have to assess the extent of the infestation – specifically, how many apartments and stairwells have ant colonies. If you report it early, perhaps only your apartment and the neighbouring ones above, below, and next door will need to be treated," says Byrkjeland.
She recommends contacting the board of the housing cooperative.
"They might have pest insurance, meaning individual residents don't have to file a claim under their own insurance policies," she says.
Poison for everyone
Anders Aak explains that the most effective method is for the ants to poison their own colony.
The poison comes in small pellets that the ants mistake for food.
"The workers that collect food bring the poison back inside and distribute it to the larvae, queens, and other ants that don't leave the colony. The poison prevents the larvae from developing and renders the queens sterile," explains Aak.
High doses of poison do not work. If the dose is too strong, the adult ants die before they can bring back more poison. If every ant does not receive the poison, parts of the colony may survive.
Pest control specialists therefore have to monitor the colonies over time and replenish the bait until they are certain that all the colonies have been eradicated.
"A single queen lays 4,500 eggs during her 39-week lifespan. If the infestation isn't stopped, the numbers can become staggering – massive colonies with millions of workers," says Byrkjeland.
Worst in hospitals
Pharaoh ants do not cause major damage in residential buildings inhabited by healthy people, but residents can carry the ants elsewhere with them.
"If a nurse accidentally brings ants to work, the consequences could be serious," says Byrkjeland.
Because pharaoh ants move between dirty and clean areas, they are particularly problematic in hospitals.
"Hospitals have countless hiding places, such as pipes, tubes, and wiring. Equipment is also constantly being moved around. If ants travel from sinks and drains to bandages and bedsheets, they can carry disease-causing bacteria with them," says Aak.
In countries where pharaoh ants live outdoors, they pose a major problem for hospitals. In Norway, only one hospital has been infested with pharaoh ants.
"That was many years ago, and the infestation was successfully eliminated," says Aak.
Shame and taboo
Ragna Byrkjeland encourages people to report infestations quickly.
"There is a lot of shame and taboo surrounding pests. People worry that it implies poor hygiene, but that isn't the case. Pharaoh ants may have arrived with goods you’ve purchased," she says.
The infestation might not even originate in your home. The ants may have come from neighbouring apartments where the presence of ants has gone unnoticed or unreported.
"We have a zero-tolerance policy for pharaoh ants in Norway," says Aak.
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Translated by Nancy Bazilchuk
Read the Norwegian version of this article on forskning.no
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