Ants in the Garden: Both Friends and Enemies

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If you garden, you’ll certainly run into ants. They are everywhere! Different species occur on all the continents except Antarctica and 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 your garden is not being overrun by aphids and caterpillars, 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, 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

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

Nobody wants to see ants inside the house. Photo: http://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 so 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

Some ants actually raise and care for aphids. Photo: http://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, don’t kill the ants: they’re the courier, not the problem! But 10 to 1 there are sucking insects of some sort in the branches above you may want treat.

Stinging Ants

Note the stinger at the end of this fire ant’s abdomen. Photo: http://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.

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 and spread rapidly throughout the south of the country. It’s limited in its northward expansion because of its inability to tolerate cold winters. 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. 

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.

This European red ant was photographed in Vancouver, Canada. It’s come a long way from its home in Western Europe! Photo: Sean McCann, http://www.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?)

Distribution of the European red ant. Ill.: James Wetterer, Wikimedia Commons

It too has taken to traveling and was apparently imported 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 where it’s established 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, neither the true fire ant nor the European red ant should be allowed 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 should 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.

When boron is mixed with sugar, ants don’t seem to realize they’re carrying home a poison. Photo: http://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 is tainted with boron.

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


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

5 thoughts on “Ants in the Garden: Both Friends and Enemies

  1. It’s critical to mention that in the UK and EU you can no longer buy borax. In 2010 the EU reclassified the ‘Borate’ group of chemicals that Borax belongs to as potentially hazardous to health, so it is no longer available as a cleaning and laundry product. Instead, you can only buy “Borax Substitute”. Borax substitute is completely ineffective for use as a means of controlling an ant infestation. We are here advised to use a general insecticide, which is obviously harmful to a wide range of insects, or ‘natural’ remedies containing vinegar or lemon juice, which succeed in merely making them move on. Even if it’s just a foot to the left….

    • Recently I had to rescue a favourite plant, a gingkho sapling which I had in a pot. The leaves were going yellow and the top growth was dying back… I removed it from the pot and found that almost the entire rootball had been stripped of soil, the roots were exposed to nothing but air, and the whole pot was one gigantic, very active and extremely productive ant’s nest. Small, red and very aggressive. I resorted to shaking the rootball thoroughly to get rid of the ants, and dunking it in a bucket of rainwater. I then – shame to say – swept all the ants up into a heap, eggs, queen and all, and put the lot into a large lidded bucket, into which I then poured 2 kettlesful of boiling water. I felt absolutely dreadful doing it, but the nest was beyond control. Drastic, but effective. The tree is now repotted and I think it will survive to tell the tale… after all, a gingkho survived the atomic bomb on Hiroshima; a bunch of red ants are going to be of little consequence…

  2. Ants are what make scale and aphid so bad in fruit trees! That is why we use Tanglefoot. (I actually just use axle grease.) Otherwise, ants are not a problem for us.

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