There are dozens of species of ants that nest in the soil of lawns, pastures, gardens, and fields in Iowa. Most species are beneficial and do not require control. However, if left undisturbed, and with good soil and cooperative weather, ants may bring enough soil from their expanding, underground colony to construct a small hill in the lawn or a truly impressive mound in the garden or pasture. These ant mounds may become a nuisance.
Ant mounds are a common sight in yards and gardens. These structures made of soil, sand, and debris mark the presence of an underground ant colony. While ant mounds themselves are mostly harmless, the ants that build them can become a nuisance. Read on to learn all about ant mounds, including what they are, why ants build them, different types of mounds, and how to get rid of them.
What is an Ant Mound?
An ant mound refers to the pile of excavated material that surrounds the entrance to an underground ant nest. It is constructed by worker ants as they dig tunnels and chambers below ground. The ants carry the displaced soil to the surface, gradually forming a mound.
The mounds come in a variety of shapes and sizes depending on the ant species. Some mounds are low and flat just a few inches tall. Others can reach up to three feet high and six feet wide! Mounds built by the same ant colony can also vary in appearance based on the type of soil.
Why Do Ants Build Mounds?
Ants create mounds for several important reasons
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Dumping excavated material: As ants dig their underground nests, they have to put the dug-up soil somewhere. Piling it up above ground to form a mound is the easiest solution.
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Temperature regulation: The mound helps insulate the nest, protecting it from extreme temperatures. Its shape facilitates air circulation as well. Some ant species even orient the mound to maximize sun exposure in cooler climates.
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Predator protection: A mound makes it harder for predators to access the nest and the ants inside. Larger mounds provide more robust protection.
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Living space: In some species, ants extend their nest into the mound itself, using it for food storage, incubation chambers for larvae, and more.
Types of Ant Mounds
There are many types of ant species that build mounds. Here are some of the most common:
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Fire ant mounds are made by red imported fire ants. They can reach up to 18 inches high and are loose, cratered mounds made of soil particles.
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Harvester ant mounds are created by seed-gathering harvester ants. They are low, broad mounds often covered in pebbles, pine needles, and other debris.
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Pyramid ant mounds are built by cone ants and get their name from the ant’s triangular thorax. They are volcano-shaped, with a central crater for ventilation.
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Carpenter ant mounds consist of excavated wood mixed with sawdust and waste. They form as the ants burrow into wood, unlike other species that dig in soil.
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Allegheny mound ant mounds are some of the largest. These can be up to 6 feet wide and 3 feet high! The ants kill nearby plants to clear space for mound construction.
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Leafcutter ant mounds are common in Texas. They are volcano-shaped and often clustered close together, with many entrance holes.
How to Get Rid of Ant Mounds
If ant mounds are popping up in your yard, here are some effective ways to get rid of them:
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Pour boiling water into the mound to kill ants and disrupt the nest.
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Use a shovel to flatten the mound so ants abandon it.
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Make a boric acid bait to attract and kill ants.
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Drown the mound by flooding it with a hose for several minutes.
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Apply dish soap mixed with water into the holes; this suffocates the ants.
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Sprinkle diatomaceous earth around mounds to irritate ants and dehydrate them.
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Apply pesticide sprays or granules following label directions carefully.
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Hire a professional exterminator for severe infestations.
Be sure to target the queen or queens to prevent ants from rebuilding. Combining methods usually works best for thorough, long-lasting control. With persistence and patience, you can banish pesky ant mounds from your landscape.
Frequently Asked Questions About Ant Mounds
Do ants live in the mounds?
Ants do not live inside most mounds. The mounds themselves are primarily made of displaced soil excavated from underground. The actual ant nest and colony exists below the mound in an extensive network of tunnels and chambers.
However, some ant species do use parts of the mound structure for housing ants, storing food, or incubating larvae. The proportion of ants inhabiting the mound compared to those underground varies by species.
How are ant mounds different from termite mounds?
While ant and termite mounds appear similar on the surface, they have some key differences:
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Composition: Ant mounds are made of soil, while termite mounds contain soil, chewed wood, and feces. Termite mounds feel spongy.
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Moisture: Ant mounds tend to be dry and loose. Termite mounds often feel damp and stick together more.
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Height: Termite mounds are generally much larger, sometimes reaching over 30 feet tall! Ant mounds rarely exceed a few feet high.
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Shape: Termite mounds are often chimney-like. Ant mounds have a more rounded, volcano shape.
How long does it take for ants to build a mound?
Ant colonies can build sizable mounds in just a few months. However, giant mounds that are many feet high can take years or even decades to construct fully. The growth rate depends on factors like the number of worker ants, soil composition, and mound purpose. Regular maintenance is needed as weather and animals damage the mound over time.
What is the largest ant mound on record?
The largest known ant mound was built by a supercolony of Argentine ants in Europe. The massive mound measured about 700 feet wide and 13 feet high! It contained approximately 30,000 entrance holes over its surface. Truly a marvel of ant engineering.
How to Manage Ant Mounds
When anthills in the lawn appear above the grass tops the mound can be raked or “washed” flat as needed (use a forceful stream of water from the garden hose to disperse the soil on a regular basis). The need for such maintenance will be greatest during periods of prolific ant nesting activity such as during periods of wet spring weather. If necessary, as a last resort, you can spot-treat anthills in the lawn with an insecticide such as Sevin, bifenthrin, permethrin, cyfluthrin, or esfenvalerate. Rake the anthill flat and sprinkle granules onto the soil surface or drench the mound area with diluted solution. Read and carefully follow the instructions on the insecticide label.
The other time ants seem problematic is when a colony digs and tunnels around vegetable transplants. Ants do not feed on the plant roots, but they may excavate so much soil from next to the plant that the roots are exposed to air and dry out, thus stunting or killing the transplant. If ants threaten your transplants and the plant is still healthy enough to recover, you can drench the soil around the transplant with a garden insecticide solution. There is no need to treat the entire garden.
Types of Ants Found in Lawns & Pastures
The ants that nest in the ground are called field ants. Many of these are “the other” big black ants. The public often assumes that “big black ants” are carpenter ants. However, carpenter ants do not nest in the soil. Instead, they nest in moist, decayed wood such as hollow trees and rotted window sills. Not all field ants are large and black; there are many small, lighter-colored field ants as well.
The soil-nesting ants found in Iowa are not biting or stinging pests (though some will bite in defense if handled carelessly). The fire ants of the southern U.S., well known for their aggressive behavior and painful stings, are not present in Iowa.