Climate warming trends and State Government urban infill policy is increasing the spread of invasive ants inside and around metropolitan Perth homes.
A study by Curtin University’s Department of Environment and Agriculture has revealed a gradual take-over of invasive ant species more suited to Perth’s increasingly urbanised areas.
The most prolific of these foreign invaders is the African big-headed ant, also known as the costal brown ant (Pheidole megacephala), considered by the International Union for Conservation of Nature to be one of the 100 “worst” invasive species in the world.
The study suggested the big-headed ant now constituted almost 60 per cent of all ants found in household gardens around Perth.
It gets worse.
The Bureau of Meteorology recorded the highest-ever number of 40-degree days across Perth this summer, since records commenced.
BOM long-term records suggest Perth’s climate is steadily warming and experiencing less rainfall each year.
With the ant loving heat and moisture, these recent climatic trends have increased the likelihood of encountering the big-headed ant inside your home now too, according to BioMonitoring International director and entomologist Jonathan Majer.
“The higher the temperatures, up to a point, the more active these ants are going to be,” said Professor Majer.
“And the drier it is the more likely it is they’re going to seek out moist places, like those found inside your home.”
Unsurprisingly, pest control companies have recorded an increase in jobs involving ant activity inside Perth metropolitan homes this past summer.
Pesti Pest Control recorded a 45 per cent increase in inside jobs, compared to the previous summer.
Owner Drew Snir says most of the time it’s the coastal brown.
“You see them mainly in wet areas, like kitchens and bathrooms,” he said.
“Normally they’ll get in through the back door and the window frames.
“You can try plugging up the holes, but they’ll just find another.”
Antipesto Ant Treatment recorded an average increase of 32 inside jobs over the months October, November, January and February, a rise of roughly 33 per cent, and a smaller increase over Christmas and the start of autumn.
“Climate change has kept them active for longer, that’s my personal theory,” says owner Ashley Firth.
“I’ve definitely done more ant jobs because it’s been a longer summer, and the coastal brown ants constitute roughly 95 per cent of the work in Perth.
“We’ve nearly reached last year’s April job figures, three weeks early, just to give you some idea of how long this pest season has been going.”
CTI Pest Control manager Paul Hinscliff also reports an increase in inside jobs and says, additionally, the growing trend he’s witnessing of ants invading bathrooms is unusual.
“I understand why they’re on a kitchen bench or windowsill, obviously they’re chasing a little bit of sugar or leftover food,” he said.
“But often now they are moving into bathrooms too.
“Possibly they’re just seeking what they can’t always get outside now, water.”
The advice from these experts is simple.
“Call us, call an expert,” says Mr Snir.
A study by Stanford University researchers of a different invasive ant, the Argentine ant (Linepithema humile) once Perth’s dominant urban pest, found an “impressive” relationship between the weather and ant abundance inside homes in California.
The study indicated hot, dry summer months correlated with a “peak” in household ant activity.
The study also suggested the ant’s ability to easily utilise households during unfavourable weather conditions might be contributing to their increasing urban populations.
Department of Agriculture and Food entomologist Marc Widmer says, similar to the Argentine ant, big-headed ants also thrive near homes and are prone to come indoors during the hotter, drier periods in search of moisture and food.
“Twenty years ago, 95 per cent of our enquiries were for the Argentine ant, but because it’s drying so much they’re less than 10 per cent of the enquiries we get now,” he said.
“The big-headed ant has catapulted and taken over that number one spot.
“We probably get about two thousand enquiries a year about ants and most of them involve the coastal brown.”
The good news is, unlike the Argentine ant, the big-headed ant is less inclined to nest indoors, with indoor activities restricted to foraging, but it does still happen.
According to a report by the department, they are most often seen nesting in lawns and brick paving around the home, “which they tend to undermine.”
Indoor “invasions” are only occasional, but can be “severe,” the department writes.
Curtin University biodiversity and insect ecologist Brian Heterick says urban infill has also played a role in the rise of the African big-headed ant.
“They flourish in areas which have been highly disturbed, which are houses and parks and gardens, or urban areas generally,” Dr Heterick said.
The State Government has set a 47 per cent urban infill target for the Perth and Peel region, to be stimulated through planning changes.
The most recent government statistics report urban infill has increased 4.5 per cent over 2010 levels.
This means we’ll probably be seeing more of these and other urban specialist ants foraging and nesting inside in the future, according to Dr Heterick.
“If you have increased infill where all the ground is covered with hard-cover such as concrete, bitumen, pavers or something like that, and the only greenery is found in small park areas, where you get non-native grasses and a few non-native trees, there is going to be very little suitable habitat left for native invertebrates,” he said.
“Nature will form a vacuum in these locations, and you’ll get the introduced ants who are more at home in these conditions moving in.
“So, if we head further down this route, we will see less native ants outside, but more species, like the big-headed ant, that are habituated to indoor dwellings.”
Mr Widmer suggests sending in your pesky invaders to the Department of Agriculture and Food for identification.
“It’s a free service, and you get expert advice as to what treatments will be most effective,” he said.
“Some ants require chemical spray, some need a protein or an oil based bait, some need a sugar bait.
“Granular ant baits work like a magic wand on the African big-headed ant, but they’re pretty expensive and will have no effect on other household invaders like the black house ant and the white-footed house ant, so consult us first.”
The identification service serves another important purpose, according to Mr Widmer.
“You’ll be helping the department keep an eye out for exotic species we don’t already have.”