Red imported fire ants have not established permanent populations in Maryland. The state classifies them as an Invasive Species of Concern, and while isolated colonies have been found, none have survived long enough to become established. If you’ve spotted what you think is a fire ant mound, you’re likely looking at a native ant species, but it’s worth knowing how to tell the difference.
Maryland’s Current Fire Ant Status
Red imported fire ants arrived in the United States from South America in the 1930s and have since spread across much of the Southeast. Their range extends reliably through states like Texas, Georgia, and the Carolinas, where mild winters allow colonies to survive year-round. Maryland sits at the northern edge of where these ants can potentially survive, and so far, the cold winters have prevented any lasting foothold.
Isolated colonies do turn up in Maryland from time to time. These typically arrive through shipments of soil, nursery plants, or landscaping materials from southern states. A colony might survive a mild season, but Maryland’s winters generally kill them off before they can spread. That said, warming temperatures could change this picture over time, which is exactly why the state treats every sighting seriously.
If you find what you believe is a fire ant, the Maryland Department of Agriculture asks that you contact them immediately. Early detection is the state’s primary defense against a permanent infestation.
How to Identify Fire Ants
Red imported fire ants are small, ranging from about 1/16 to 1/5 of an inch long. One distinctive feature is that workers within the same colony come in noticeably different sizes. Their bodies are reddish with a darker, shiny brown rear section, and they have a visible stinger. Their antennae have ten segments ending in a two-segment club shape.
The mounds are often the easiest giveaway. Fire ant mounds are built in open, sunny areas near water sources and lack a central entrance hole on top. Instead, ants enter and exit through multiple openings around the base. Left undisturbed, a mound can grow to 18 inches high and 24 inches wide, developing a dome shape after two to three years. Colonies can house up to 500,000 workers with multiple queens.
If you disturb a fire ant mound, you’ll know it quickly. The ants swarm out aggressively and attack in large numbers. This behavior sets them apart from most native Maryland ants, which tend to scatter rather than mount a coordinated assault.
Ants You’re More Likely Seeing
Several native and established ant species in Maryland build visible mounds or have a reddish color that can cause confusion. Allegheny mound ants create large, dome-shaped dirt mounds in fields and yards that can look alarming but are not fire ants. European fire ants (a completely different species from imported fire ants) have been found in parts of the mid-Atlantic and do sting, though their colonies are much smaller. Common pavement ants, which nest in cracks and along sidewalks, are dark brown and far less aggressive.
The key differences to watch for: true red imported fire ants build mounds without a visible top entrance, contain workers of varying sizes within the same colony, and respond to disturbance with immediate, swarming aggression. If the ants you’re seeing have a single, obvious hole at the top of their mound or are all the same size, they’re almost certainly a different species.
What Fire Ant Stings Feel Like
Fire ant stings are distinctive enough that the sensation itself helps with identification. The initial feeling is a sharp burn at the sting site. Within about an hour, itchy bumps or welts develop, often arranged in a circular or semicircular pattern where multiple ants stung at once. These welts last several hours.
The telltale sign comes next: after several hours, the bumps turn into small blisters. About a day later, those blisters fill with white or yellow pus-like fluid. This progression from burning to welts to pus-filled blisters is unique to fire ant stings and doesn’t happen with most other ant bites. The blisters resolve on their own within seven to ten days. Don’t pop them, as breaking the skin increases infection risk.
For mild stings, washing the area with soap and cold water and taking an over-the-counter antihistamine for the itching is usually sufficient. Cold compresses and hydrocortisone cream can also help. A small percentage of people experience a systemic reaction with symptoms like stomach cramps, nausea, swollen tongue, or difficulty breathing. In rare cases, fire ant stings trigger anaphylaxis, a severe allergic reaction that requires emergency treatment.
Treating a Mound if You Find One
If you discover what appears to be a fire ant mound in Maryland, contacting the Department of Agriculture is the first step since the state tracks every occurrence. But you may also want to deal with the immediate problem, especially if the mound is near where children or pets play.
The most straightforward home method is pouring two to three gallons of very hot or boiling water directly onto the mound. This kills the colony about 60% of the time. When it doesn’t work, the surviving ants typically relocate rather than rebuild, so you may need to repeat the process. Be aware that boiling water will kill any grass or plants it touches.
For chemical treatment, dust products work fastest and don’t require water, though they leave visible residue. Liquid drenches can eliminate a mound within hours. Granular products are applied on and around the mound, then activated by sprinkling one to two gallons of water over them without disturbing the mound itself. With any product, the critical detail is to avoid stepping on or poking the mound first. Disturbed colonies will scatter and relocate before the treatment reaches the queen.
In southern states where fire ants are widespread, experts recommend a two-step approach: broadcasting bait insecticide across the entire yard between late August and mid-October, then treating individual mounds as they appear. For Maryland, where you’re likely dealing with a single isolated colony rather than a yard-wide infestation, individual mound treatment is usually all that’s needed.