Beneficial insects Gardening Harmful insects

Ants: The Insect Frenemies of the Garden

Messages have been pouring in over the last few weeks from panicky gardeners who’ve discovered ants in their gardens or lawns and who are convinced it’s a calamity of biblical proportions. Yet ants are not usually a major problem for gardeners. In most cases, in fact, you can simply ignore them. I figured it was worthwhile republishing this article from July 10, 2019 to calm things down a bit. LH

By Larry Hodgson

If you garden, you’ll certainly run into ants. They are everywhere! Different species occur on all the continents except Antarctica. And you find them in all imaginable environments, from deserts to swamps and from the tropics to the frozen North. While some people are horrified by their presence and insist on eliminating them at all costs, a wise gardener will learn to tolerate them, reacting only when they cause a real problem.

It’s important to understand that ants are both beneficial and harmful … and for the most part, it’s the beneficial side that takes precedence.

On the Plus Side

Ants as Predators

Few gardeners suspect the major effect the ants wandering their yard can have on other garden pests. If aphids and caterpillars aren’t overrunning your garden, it’s often because the local ant population has been nipping such infestations in the bud. Many ants are predatory and avidly hunt small insects and other creatures: flea beetles, earwigs, slugs, etc. Or eat their prey’s eggs, keeping populations down. Some plants (the peony is the best-known example) even offer nectar and other resources to ants. That’s because their presence repels insects that can harm them. In former times, farmers used to encourage the presence of anthills in their fields as protection against the really serious pests.

Ants as Bird Food
The northern flicker (Colaptes auratus) is particularly fond of ants. Video: Pets, Animals, Travel, Docs, & Rare Musical Stuff, http://www.youtube.com

Ants help a lot of useful animals indirectly by serving as a food source. All sorts of insect-eating birds, including woodpeckers, grouse and wrens, feed on ants, and so do other animals: toads, lizards, shrews, and many, many more. And we want these insectivores in our gardens, as they keep other pests under control. So if you can tolerate ants, just their presence helps maintain a healthy population of pest eaters.

Detritivores

If you take the trouble to observe ants, you’ll see them carrying all sorts of “junk” back to their nests: petals from faded flowers, dead insects, weed seeds, etc. They are, in fact, Mother Nature’s cleanup crew, like mini vacuum cleaners! Carpenter ants go even further and help decompose dead wood (stumps, roots, etc.), not only by digging tunnels into the wood, but also by transporting fungi and bacteria that contribute further to the wood’s decomposition. That way, they free up space for other cultures.

Soil Aerators
Ant tunnels in soil
As they dig their tunnels, the ants aerate the soil. Photo: colleen721, DeviantArt

Most anthills are above ground where you can see them, but what you don’t see as easily is the whole series of galleries ants dig underground as they tunnel to often quite impressive depths and distances. These tunnels improve air and water circulation to plant roots and are therefore a plus for your garden.

The Downside of Ants

So, ants can be very useful to our gardens, but sometimes they cause trouble too.

Ants Indoors
Ants inside a home.
Nobody wants to see ants inside the house. Photo: www.consumerreports.org

Whatever good ants may do outdoors, they are not wanted indoors. When ants wander into your home, you have every right to want to drive them away, even if they only steal a few crumbs from the pantry. 

But food theft is probably the least of your worries. What you really don’t want indoors are carpenter ants. They can be a real nuisance indoors, as they don’t see the difference between an old stump you don’t mind them helping to decompose and the wood that holds your house upright. Their tunnels and nests can do serious damage … and they are very hard to eliminate. This is the kind of situation serious enough that you may want to call in an exterminator.

Farmer Ants
Ants taking care of aphids.
Some ants actually raise and care for aphids. Photo: www.planetnatural.com

The same ants that protect our garden plants from some insects and pests may also be raising others on the side. Such is the case with some sucking insects such as aphids, scale insects and mealybugs. These insects secrete a sweet liquid called honeydew that ants love. They go so far as to milk (figuratively speaking) sucking insects to stimulate a greater production of honeydew. They’ll defend these “insect cows” against their predators (ladybugs, lacewings, hoverfly larvae, etc.) and can even transport their food source from one plant to another to start a new colony. 

There is at least one advantage to this ant husbandry: it often leads you to discover where the sucking insects are hiding. If you see a procession of ants climbing into a tree or shrub, and especially if they then come back down with a clearly swollen abdomen, don’t kill the ants: they’re the messenger, not the problem! But 10 to 1 there are sucking insects of some sort in the branches above that you may want treat.

Stinging Ants
Fire ant with its dard pointing up.
Note the stinger at the end of this fire ant’s abdomen. Photo: www.npr.org

Then there is the problem of stinging ants, species that you would not want to have in your gardens because of their aggressive nature and their painful sting. 

Now, many ants will bite with their mandibles if you bother their nest, but usually you can simply brush them off, no serious harm done. But stinging ants have a stinger like a wasp or a bee and they don’t hesitate to use it both on humans and pets. They tend to be naturally aggressive and it doesn’t take much to annoy them. Mowing the lawn, weeding the garden or hanging clothes on the line near one of their nests may become unthinkable and you certainly won’t be able to let children play outdoors when they are around.

Fire ants on a piece of wood.
The fire ant is a tiny reddish ant that doesn’t look that impressive, but its size belies its aggressive nature. Photo: Scott Bauer, Wikimedia Commons

The most famous stinging ant is the fire ant (Solenopsis invicta), also called the red imported fire ant (RIFA). This tiny reddish ant was introduced by accident to the United States from South America in the 1930s. It then spread rapidly throughout the south of the country. Its inability to tolerate cold winters limits its northward expansion, though. Still, give it a mild winter or two and it will move well up into more temperate areas. It is now also found in Asia (Hong Kong is experiencing a major infestation), in Australia and in the Caribbean. 

Map showing fire ant distribution around the world.
Fire ants are becoming a planetary issue as they migrate from country to country. Ill.: James Wetterer, Wikimedia Commons

The fire ant is considered one of the worst invasive species on the planet. It is very aggressive towards humans and pets, racing out its nest by the hundreds if you manage to step on it. When it stings you, you’ll know why it’s called “fire ant”: the burning sensation is excruciating. It actually injects venom when it stings, like a wasp, causing skin rashes, blisters and pustules. Sometimes people end up in the hospital. And a very few, unfortunately, are allergic to the stings and need immediate treatment for anaphylactic shock or they can die.

 European red ants
These European red ants were photographed in Vancouver, Canada. They’ve come a long way from their home in Western Europe! Photo: Sean McCann, flickr.com

Another stinging ant is the red ant or European red ant (Myrmica rubra), common throughout most of Europe, including Great Britain. It’s a very nasty ant, but its stings aren’t nearly as serious as those of the fire ant. Unfortunately, the press has taken to calling it European fire ant, leading people to confound the two. (“Fire ant” just sounds so much more dramatic that “red ant,” doesn’t it?)

Map showing European red ant distribution around the world.
Distribution of the European red ant. Ill.: James Wetterer, Wikimedia Commons

It too has taken to traveling. Sailors apparently imported it accidentally to Maine over 50 years ago. A much hardier ant, it can survive Scandinavian winters in the wild, so there is not much to stop it in the US and Canada. You can now find it here and there, notably in Maine, Massachusetts, New York, Pennsylvania, New Jersey, Washington D. C., Rhode Island, New Hampshire, Ontario, Québec, New Brunswick and Nova Scotia. It has has shown up most recently in Washington and British Columbia.

Because of their dangerousness, you shouldn’t allow either the true fire ant or the European red ant free rein in any garden. Both, too, are very hard to eliminate, as they tend to make multiple nests that cover large areas, so you’ll have several nests to control, some often in a neighbor’s garden.

With stinging ants, the best treatment is to call in an exterminator.

Controlling Ordinary Garden Ants

Returning to more typical garden ants, the ones that aren’t threatening to humans: in most cases, it’s best to simply learn to live with them. At mentioned at the beginning of this article, they tend to be more beneficial than harmful. And you’ll never get rid of them all anyway. Even if you wipe out a few colonies, more will move in. So, live and let live: that’s the attitude a good laidback gardener should take.

In the rare cases where ants really cause you problems and you absolutely need to eliminate an anthill, any hardware store or garden center will offer you a wide range of ant control products you can use. In most cases, the active ingredient is boron, a natural element that is toxic only at high doses. The secret to using boron is that the bait must only contain only a weak dose. That way the worker ant won’t be poisoned and can safely carry it back to the nest, which is what you want. With workers feeding the queen small amounts of poison on a regular basis, she eventually dies and then the colony disappears.

Small mound of white boron crystals.
When boron is mixed with sugar, ants don’t seem to realize they’re carrying home a poison. Photo: www.indiamart.com

If you prefer a homemade recipe, mix try mixing 1 teaspoon (5 ml) of borax (a cleaning product sold in supermarkets and supermarkets) or of boric acid (a sterilizer sold in pharmacies) with an equal amount of icing sugar. Pour the mixture into a container so that the bait is protected from the rain (for example, an empty soda or beer can) and place it near the nest you want to eliminate. The ants will find the sugar and carry it back to their queen without noticing that it contains a portion of boron.

Boron treatments take three to four weeks to be effective, so you have to be patient.

Let Nematodes Help You
Commercial nematode product.
Commercial nematode treatment. Photo: Premier Tech Home & Garden

You can also control ants with commercially available nematodes. Treat the soil with the product, following the instructions on the label. After that, the nematodes, which are microscopic worms, will attack and kill the larvae and eggs of the ants. And that gradually puts an end to the colony. This may take a few weeks and a second application is sometimes necessary.


Ants: sometimes they’re our friends, sometimes they’re our enemies, but in most cases, you really don’t need to control them.

Garden writer and blogger, author of more than 60 gardening books, the laidback gardener, Larry Hodgson, lives and gardens in Quebec City, Canada. The Laidback Gardener blog offers more than 2,500 articles to passionate home gardeners, always with the goal of demystifying gardening and making it easier for even novice gardeners. If you have a gardening question, enter it in Search: the answer is probably already there!

4 comments on “Ants: The Insect Frenemies of the Garden

  1. marianwhit

    Great piece…we are taught to freak out by people trying to sell us pesticides. My line is drawn at the inside of the house. This is rarely a problem because I patrol the outside and inside in spring and fall sealing openings and checking for chronically wet wood, which is an open invitation to carpenter ants. We make sure to leave a lot of fallen trees etc. around where they are not a hazard so the carpenter ants are not assaulting our homes. Most people don’t realize that by making a “sterile” yard with just a lawn makes them desperate for habitat…and the only thing that look good…is the house. This seems counter-intuitive, but is true..and our reward is the pileated woodpeckers and flickers which are “ant specialists”. Thank you!

  2. Christine Lemieux

    I have a lot of ants in my gardens. Live and let live is how I go, except when they build up the soil in an ornamental grass, for example, which kind of chokes the grass out. They also farm a lot of aphids here! I just squish if the numbers are too high. Every year is different!

  3. An interesting article. Bugs of any kind, especially large numbers, just seem to panic people. As we live out in the country there are lots of ants, small black one all the way up to big red ones (the most aggressive but only bite not sting). There are several large nests back in the woods and it’s cool to watch their progression. Some of the nests are almost a meter tall now. We pretty much leave them alone until some entrepreneurial group tries to move in to the garden. Thankfully we are too cold for fire ants.

  4. Derek Bull

    Last year I had two rows of beetroot ‘felled’ by black ants, just as they were producing their true leaves. They started on this years rows as well so had to spray a line of ant killer each side of the rows to keep them off! Mind you the other day I also saw some dragging a centipede back to their nest so good on them!

Leave a Reply

Sign up for the Laidback Gardener blog and receive articles in your inbox every morning!

%d bloggers like this: