ant hills in yard

Why Are There So Many Ant Hills in my Yard?

In Lawn & Garden by Jamie

Ants are fascinating and in general, are beneficial to your yard, but as gardeners, our knee-jerk reaction seems to be “bug bad.” There are times when you do need to move an ant population, but there’s also many times when it’s best to just leave them alone.

Ant hills are caused by ants digging out tunnels beneath the surface and bringing up that excess soil to the nest entrance. Ants don’t live in the ant hill. Ants may be attracted to your yard because:

  • Depending on the species, they like to nest in sandy and dry soil, moist or decaying wood, and patchy, struggling lawns.
  • There’s a lot of aphids and/or mealybugs, who produce honeydew that ants like to eat.
  • They’re already nesting there but are digging new tunnels and entrances.

What causes ant hills in your yard?

When ants dig their tunnels under the ground, the soil has to go somewhere. The nest isn’t actually the ant hill or mound. The hill or mound is just excess soil. The nest is actually in the tunnels.

Not all ants make ant hills. Some species of ants live underground, but others live under leaves or even solely in trees.

Why are there so many ants?

It may not be that there are actually more ants in your yard, only that it appears to be more. Ants are most active between spring and summer when they hunt for food.

When it rains, tunnels are flooded and tunnel-dwelling ants are forced to find shelter, usually by foundations, siding, and window sills. Either way, you’ll see more ants, but there are not actually more ants. They were just hidden away from human view.

Are ants in the yard bad? Do ants damage your lawn?

Ants are like weeds. Sure we gardeners rail against them and despair, but outside of a few noxious species, they’re a natural and even beneficial part of the ecosystem. Most ants don’t harm your garden or lawns in any way, and, in fact, provide a lot of benefits. The exemption are species like fire ants, which are invasive, and other biting and stinging species.

Benefits of ants and ant nests include:

  • Ant nests aerate the ground because they dig tunnels.
  • Ants fertilise your plants with their excrement. Their excrement contains amino acids and urea, chemicals that people pay a lot of money to spray on leaves as fertiliser.
  • Ants collect dead insects and eat the larvae of pests.
  • Trees attract ants with nectar so that the ants, as they journey to the nectar, will destroy pest insects that would otherwise damage the plants.

The only time that ants may damage plants is if their aerated nests dry out the soil beneath vulnerable plants or if they’re farming aphids. Yes, ants farm aphids like tiny cattle ranchers, collecting for food the honeydew that aphids produce. (Don’t tell me you don’t find that cool.)

In this case, it’s actually the aphids that are hurting plants. Spray the affected plants with castille soap and water to get rid of the aphids. Once the aphids are gone, the ants will go away.

For lawns specifically, the other difficulty is that ant nests can raise the soil level that makes mowing inconvenient. Or, if you’re married to the idea of the ideal lawn, ant mounds can look unsightly.

But if the ant species bites and/or stings and they’re nesting near a space where you and your family use, then you’ll probably want to encourage them to kindly move on.

What are undesirable ants?

While no ants are “bad”, there are ants that are noxious to humans. They aren’t out to get you, but will bite to defend their territory or protect their nestmates. These species are generally either ants that bite and ants that bite and sting.

You’ll know the difference between an ant bite and an ant sting because you’ll feel a sting for hours after.

Fire ants will defend their territory by biting and injecting chemicals that cause allergic reactions. (They are also a destructive invasive species.) Not all red ants are fire ants! Before you panic, learn how to identify fire ants.

Harvester ants are aggressive and sting multiple times, causing minor pain that subsides within a few hours.

Field ants, crazy ants, and carpenter ants (one of the largest species) all bite when threatened.

Identifying ant species can be difficult but if you’re getting bitten or stung, then that’s bad. Where the ants nest can also tell you what species they are.

How do you get rid of ant nests in grass?

Getting rid of all ants in your yard and keeping them out is impossible, and not advisable. They’re going to come back. At best, you may be able to encourage an ant nest to move.

Are your ants actually a problem?

Before you take any action, determine whether you actually need to.

Are the ants:

  • Accidentally killing the plants that they nest under through drying roots?
  • Biting and/or stinging you and are nesting in a place in the yard that you or your family use frequently?
  • Nesting in the foundations or walls of your house?

If so, then you may need to move the ants. If not, they’re probably fine where they are.

If the problem is ant mounds in the middle of your lawn, you have two choices:

1) Let go of the picture-perfect lawn

If the only reason you want to get rid of an ant nest is because it ruins the picture-perfect lawn, then the best way to deal with it is to let go of the image. The lawn is fine. Spend the time and frustration that you’d otherwise be using trying out different solutions on something more relaxing than battling nature.

Or take a look at suggestion #1 in the next section.

2) Rake the mounds to a ¼” over grass on a weekly basis

Keeping soil in a mound to ¼” will help keep the grass under the mound alive and you won’t see a mound anymore. Remember, the ants aren’t actually living in the mounds. They’re just the aftermath of their tunnel digging. Even if you cover up the tunnels, the ants will have other tunnel entrances to use, hopefully in more discrete locations.

If you need to move the ants due to biting, stinging, or inadvertent plant death:

None of these are going to wipe out the whole colony. You may need to repeat these treatments in the future if the ants move back in.

There’s also a lot of organic “solutions” being touted that don’t bear out at all. These three solutions have been proven to effectively move or suppress ant nests.

1) Change the nesting habitat

Ant species have their own preferred nesting habitats. Carpenter ants, for example, prefer decaying wood. So if you have a rotting log in your yard, removing it will force the carpenter ants to find someplace else to live.

For ants that prefer sandy soil or patchy grass, treating with compost over the long will change the soil type and keep those ants from coming back. Or even replace your struggling lawn with a new garden bed or a hardier native species lawn.

This approach will take longer, depending on the nesting habitat, but at the very least, will keep the undesirable ant species from returning.

2) Dust Diatomaceous Earth in nest openings

Diatomaceous Earth is one organic-friendly pest control method that’s made from the skeletal remains of marine creatures. When an insect touches DE, the DE absorbs the waxing material that keeps the insect hydrated. The insect dries out and dies.

DE must be dry to work (although it can get wet and still work when it dries again) and insects must come in contact with it.

To apply, dust DE into nest openings. As ants enter the nest, they’ll carry the DE further into the nest, affecting more ants.

DE will help move ant colonies. It will not kill an entire colony.

3) Mound drench with citrus oil

D-limonene is a natural component of citrus peel oil that is toxic to fire ants. Studies [PDF] have shown that citrus oil applications can get rid of up to 80% of a fire ant colony.

To apply, mix 1.5fl oz Citrus Orange Oil and 3 fl oz of soap. (This is enough for one mound.) Soak the mound completely, making sure that you cover all the visible tunnel openings.

4) Mix borax with sugar or honey (but make sure your children and pets won’t eat it!)

Borax is poisonous to ants, but will also kill plants if you use too much. Borax is generally human-safe, but make sure that you, your children, and your pets DON’T EAT it. If you’re teaching kids to eat out of your garden, avoid, avoid, avoid. If you have a dog that’ll eat anything, avoid, avoid, avoid. Or place it near the nest where children and pets can’t access it.

To apply, mix borax with sugar (or honey) and place it near the nest. The ants, thinking they got a free food source, will take the mixture back to their nests.

Final Thoughts

Ants are fascinating insects that provide a lot of benefits to your yard. Learn to live with a few mounds on your lawn. But if they bite or sting, it’s time to move them on.