¡Argentine Ants!
(Grab a nice beverage and settle in. There’s a lot to unpack here.)
There are about 270 species of ants in California. But I’m focusing on Argentine ants because they’ve gained pest status in our homes and gardens, across agriculture and in natural areas, where they also outcompete native ant species.
Argentine ants, like other ants, are on mission to find food for their nest mates and queens. If we understand their process for finding and sharing food, then the tactics we employ for their control can be more effective for long-term management. Here, you’ll find information on biology and behavior, nest elimination tactics, a DIY bait, and exclusion techniques to help keep these persistent pests away. The management topics below are linked to the main Argentine Ant Management page.
Ant Biology and Behavior
I begrudgingly admire Argentine ants. No, I don’t like it when they invade the house. No, I don’t like it when they infest the yard and disrupt biological control. And, no, I don’t like that they outcompete native ant species and disrupt ecological systems. But I have to acknowledge that these ants are survivors. They are highly adaptable, and have successfully established across much of the globe. Argentine ants are such a common pest that you won’t have to look too hard to find someone to commiserate with. And as annoying as they are, it could be worse, at least they don’t sting or have a painful bite.
I am frequently asked about how to deal with Argentine ants. There’s a lot to it, so I wanted to write it all out in one place. The goal here is to provide insights into how ants survive and thrive, then use that information to suppress their numbers to a point where they’re no longer a nuisance.
As in any pest management strategy, identification is the first step.
Ant Identification
In California, we have about 270 species of ants, and only a fraction - 8 of them - are considered pests. Here’s an online identification guide for ants to take a closer look.
Most likely, if you see dark brown ants in your house, they are Argentine ants, Linepithema humile (Mayr, 1868).
Are they from Argentina? Yes, these ants are indeed from Argentina. They arrived in the US in 1891, first in Louisiana, then California in 1905. Argentine ants have since spread throughout most of the US and much of the rest of the world. This widespread distribution means that these are highly adaptable creatures, and they can survive under pretty much any conditions. Though, they do best in arid areas like California because the climate is similar to their area of origin.
So, why do they collect in kitchens, fruit trees and other landscape plants? Why do they return year after year, even after being treated with insecticides, fumigants and other ant control measures? In a word, trophallaxis.
Trophallaxis
To get to the heart of the ant’s tenacity, we need to understand just one word – trophallaxis. The term trophallaxis comes from the Greek words trophe = nourishment and allaxis = exchange. It was first used by entomologist William Morton Wheeler in 1918 to describe the exchange of liquid food between members of insect colonies, particularly ants.
Watch this short video to learn about key details of an ant’s biology and behavior before going on to the control section. It’ll help you understand why and how the control measures work and that will make the process of managing them more effective.
In the video, I explain:
Nests are made up of many workers and queens - not just one queen
When searching, ants leave behind a chemical trail that helps them and others find food sources and navigate back to the nest
Trophallaxis - regurgitating food to feed colony mates back at the nest
Recruitment - how they maximize the number of worker ants that follow a trail to a food source
Surviving floods and establishing new nests
Argentine ants are most often seen when they are out searching our plants and homes for resources. We can spray them or wipe them up, but as explained in the video, there are thousands more in the nest ready to replace them. So what can be done?
Below is a summary of key points for managing ants indoors and outdoors, using nest elimination techniques and exclusion techniques. Click on Argentine Ant Management for details on the points summarized below.
Managing ants requires a strategy. And fair warning, it takes time, effort and diligence. There is no quick and easy way to do this. It’s you against hundreds of thousands of foraging ants who never stop looking for food and a multitude of queens who never stop producing offspring (up to 60 eggs per day per queen).
Follow the ant trail to see where they’re coming in through the wall
Seal the opening with caulk
Clean up the ants and eliminate their chemical trail using warm soapy water or a household cleaner
Go outside and seal up any cracks the ants are using to get indoors
More work must be done outdoors for best results
Locate ant nests by following ant trails or using a garden hose
If using the hose, have a strategy for eliminating the ants that bivouac
Eliminating nests requires eliminating queens, which can be done using one of two nest elimination methods
Either the boiling water method
Or baits, commercial or DIY
Maintenance - to keep ant numbers down, use bait stations around your home, but be prepared to use these for months or even years, otherwise the ants will bounce back in no time.
Exclusion - There are three exclusion techniques to reduce their access - caulking for cracks in structures, Tanglefoot for trees, and trimming plants away from structures.
You do not need to seal up every single crack in your home, just the ones the ants are using
Ants will set up temporary nests in wall spaces of a home, caulking outside will help prevent the establishment of interior wall nests
Use Tanglefoot to prevent ants from crawling up into tree canopies
Trim plants away from structures to eliminate ant bridges
Summary
Understanding ant behavior helps focus control methods for greater efficacy. Having a variety of control options helps tailor management strategies for individual circumstances. Understanding that you can’t eliminate or eradicate all the ants from your property relieves you of a lot of unrealistic expectations. You’re developing and maintaining barriers and keeping the ant numbers down. Understanding that it takes time, effort, money, and know-how helps you to plan and keep things in perspective.
If you can manage to reduce Argentine ant numbers in your yard sufficiently, that will allow other native, non-pest ant species a chance to come in and compete with Argentine ants. You will have allies that will apply additional pressure to Argentine ants to help keep their numbers down, even if you relax your efforts over time.
Sources:
Markin, George P. (1969). "The seasonal life cycle of the Argentine ant in southern California". Annals of the Entomological Society of America. 63 (5): 1238. doi:10.1093/aesa/63.5.1238.
Moffett, Mark (2010). Adventures Among Ants: A global safari with a cast of trillions. Berkeley and Los Angeles, CA: University of California Press. pp. 203–205. ISBN 978-0-520-26199-0 – via Internet Archive (archive.org).