Help! Ants are Destroying My Lawn!

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20150814AMaybe they are, but maybe they aren’t. There are all sorts of ants, some that do great damage to lawns and some, like fire ants, you wouldn’t want to have anywhere near a lawn or garden, but the most common lawn ant in most areas is the yellow meadow ant (Lasius flavus), a small reddish brown ant that may be more of an annoyance than a real threat to your lawn, or another species of meadow ant (Lasius). Its cousin, the pavement ant (Tetramorium caespitum), introduced from Europe, has a similar life style and may the most common small brown ant in certain urban areas. I’m treating them here under the name “small brown ants”.

More About Small Brown Ants

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Yellow meadow ant: it isn’t really yellow, but that’s its name.

This type of ant makes small crater-shaped mounds of soil particles with an entrance hole in the center. You’ll find it just about everywhere in urban, suburban and grassland areas: in lawns, of course, but also in flower beds, vegetable gardens and fields. However, the nests are rarely noticed where vegetation is high. It’s when these ants set up shop in areas with vegetation is short, such as a lawn, or absent, such as a patio, that you notice them.

Each nest is usually a single colony with a queen well hidden under the ground and dozens of workers that leave the nest in search of food.

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Commercial ant bait.

Sometimes worker ants enter our homes in search of food (they love sugary foods above all else) and so kitchens and cupboards are favorite spots. They don’t live indoors, though: you’ll see them coming and going from outside. While they are annoying (who wants to see an ant in their sugar bowl?), they are not particularly harmful per se and are best controlled by sealing the cracks and crevices through which they move into the house (try silicone caulking). Or apply diatomaceous earth, an organic insecticide, around doors and windows, baseboards or cracks. Commercial ant bait also works well.

Sometimes on summer evenings you see these ants swarming: hundreds of winged queens take to the air all on the same night, attracting gulls who come to feast on them. It’s a surprising example of how Mother Nature works and one well worth explaining to children. The flying queens mate in the air with the much smaller drones (males), then land, lose their wings and start a new nest. Fascinating!

Small brown ants are essentially harmless. These are nature’s garbage collectors: they collect waste (dead insects, bits of fallen leaf, seeds, crumbs, etc.), keeping your yard neater. They are also predatory and prey on harmful insects. So far, so good, but…

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Ant feeding on aphid honeydew.

These ants do have their down side, though. They are very fond of aphid honeydew (the sugary waste aphids exude) and will protect aphids from their enemies. Sometimes they’ll even move aphids from one plant to another, which is not a good thing. However, if you keep your eyes peeled, you can actually use the ants to locate otherwise invisible aphid colonies. If you see many ants moving up and down the same plant, aphids may well be hiding in its foliage. In such cases, I suggest treating the aphids (a strong spray of water will usually get rid of them) and letting the ants be.

But What About My Lawn?

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In a lawn mowed too short, ant nests are very visible.

Small ant nests like those of the yellow meadow ant and the pavement ant don’t destroy grass: it will grow perfectly well despite their presence and in fact, possibly even better, as ants help aerate the soil. The easiest solution is just to let the grass grow taller, which thus hiding the nests from view! Actually, if you can see the nests of ants in your lawn, you’re probably mowing the lawn too short.

Lawn grasses grow best when they’re allowed to grow taller. This encourages deeper root growth and shades the grasses’ roots, keeping weeds down and protecting their roots from sun damage. For a healthy lawn, never mow less than 3 inches (7.5 cm) high… and at that height, you won’t even see the ant nests!

Note also that lawn ants a source of food for birds. Get rid of the ants and bird visits will drop. Too bad!

When ant nests appear in patios and sidewalks, they’re much more visible than in lawns. Still, I suggest just ignoring them. After all, do a few small piles of sand really do you any harm? If you simply can’t tolerate them, you could try pouring boiling water into the nest. If it kills the queen, the colony will die. Note that you can’t treat ant nests in a lawn with boiling water, as it will kill the grass too.

Bigger Nest, Bigger Problem

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Field ant nest

Sometimes you’re not dealing with little brown ants, but larger ones, often black, although they can be brown or reddish. Most of these are “field ants” (Formica spp.). They form larger colonies and bigger nests with several entrances and exits, and they will indeed harm the grass in that sector. If you are a stickler for perfect lawn, they may deserve treatment.

If you want to try to controlling field ants (and indeed, almost any ant), here’s a trick that is usually effective. Slowly pour 2 tablespoons (28 ml) of borax and 1/4 cup (60 ml) of sugar into 1/2 cup (125 ml) of hot water, stirring as you go so form a syrupy solution. Place small saucers (a bottle cap, for example) of the solution near the ant nest. (Keep any surplus in the fridge in a closed container for future use.) Boron (of which the natural mineral borax is composed) is slightly toxic and therefore the solution is also slightly poisonous. Not enough to kill the worker ants immediately, though… and that is important. The workers, attracted by the sweet solution, will bring droplets of it to the queen. As she is fed boron day after day, she will eventually be poisoned and die. And with no queen, the colony will be abandoned. But be patient! It can take up to 2 weeks to see results.

Note that the sugar and borax solution will also be slightly toxic to both humans and animals: don’t use it around children or pets.

Personally, I am not so infatuated with my lawn that I feel the need treat to field ants that move into it. After all, usually only a small section of lawn is affected, just creating a bit of a barren spot. I simply mow right over it, flattening it a bit. And if I choose to ignore their nest, field ants will help keep my yard clean and reduce predators. Live and let live: that’s my motto.

Such an ant colony will probably thrive for several years, then decline and disappear and the lawn grasses quickly move back in. Of course, by then a new colony will probably start up elsewhere…

Carpenter Ants

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Carpenter ant.

As for carpenter ants (Camponotus spp.), rather large black ants that make their home in wood, including in the timber of our houses, that’s another subject entirely. Here is a blog you might find helpful.

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