Side
by side.

Solenopsis invicta

Linepithema humile

Tapinoma sessile

Southeastern U.S. from Virginia to Texas, west to southern California; USDA quarantine zone.

Warm temperate U.S., entire West Coast, Southeast, Gulf Coast, mid-Atlantic.

Throughout the United States and southern Canada.

Polymorphic workers, 1.6–6 mm; reddish-brown head and thorax, darker gaster.

2.2–2.8 mm; uniform dull medium brown, monomorphic.

2.4–3.3 mm; uniformly dark brown to black, monomorphic.

Earthen dome mounds in sunny, open ground, lawns, pastures, roadsides, parks, athletic fields, levees, electrical boxes.

Outdoors in shallow soil nests under stones, mulch, irrigation pipe, sidewalks; readily moves indoors during rain or summer heat.

Wall voids, behind siding, under flooring, in insulation, beneath stones, mulch, logs, and potted plants.

Omnivorous: insects, oils, sweets, carrion, seedlings, small vertebrates.

Sweets and honeydew dominant; broad omnivore.

Strongly attracted to sweets and honeydew; also greases and dead insects.

Yes, burning sting followed by a sterile pustule within 24 h; anaphylaxis possible.

No.

No, defends with foul odor when crushed.

Polymorphic workers ranging from 1.6 to 6 mm in a single colony, reddish-brown with a darker abdomen, two petiole nodes, a ten-segmented antenna with a two-segmented club, and a prominent stinger. Mounds are dome-shaped, fluffy, and have no central entry hole, workers enter through subsurface tunnels. Disturbing the mound triggers a fast, aggressive swarming response with thousands of workers boiling to the surface, the single most reliable field test against the look-alike native fire ants (S. xyloni, S. geminata).

Uniform dull medium brown, 2.2–2.8 mm, monomorphic. Single petiole node clearly visible in profile (separates from odorous house ant, where the node is hidden under the gaster). Twelve-segmented antenna, no club. No odor when crushed (separates from ODH). Trails are heavily marked, persistent, and follow physical edges, sidewalk cracks, irrigation lines, baseboards.

A small, evenly dark brown ant 2.4–3.3 mm with one node hidden under the gaster (the gaster overhangs and conceals it in profile, a key separator from Argentine ants, which have a clearly visible node). Twelve-segmented antennae with no club. When crushed, workers release a distinctive rotten-coconut or blue-cheese odor; this is the fastest field confirmation.

Medically important: stings cause pustules, secondary infection, and anaphylaxis in sensitized individuals; multiple fatalities per year in the U.S. Damages electrical equipment (HVAC, traffic signals, well pumps, irrigation controllers) where workers chew insulation and short contacts. Suppresses native ground-nesting wildlife, displaces beneficial arthropods, and injures livestock, pets, and ground-nesting birds. Federally regulated: nursery stock, sod, hay, and soil-moving equipment from quarantine counties require certification.

Single most common structural ant in coastal California and a major pest across the Gulf. Heavy trailing in kitchens, bathrooms, garages, and around pet food. Displaces native ants and disrupts pollination networks. Damages drip irrigation by farming root aphids.

Primary nuisance pest in kitchens, bathrooms, and pantries; not a stinger and not a structural destroyer, but trail densities can be extraordinary and recurrent. Often tracked indoors after heavy rain saturates outdoor nests. Frequently mis-treated as 'just sugar ants' with repellent over-the-counter sprays, which causes budding and a worse problem the following week.

Texas A&M's 'Two-Step Method' is the operational standard for residential and turf settings. Step 1: broadcast a fire-ant bait over the entire property in late spring and early fall when soil temperatures are 70–95°F and ants are actively foraging (test with a potato chip). Step 2: treat individual problem mounds 7–10 days later with a contact mound treatment. Avoid disturbing mounds before bait uptake. In large pastures or sensitive sites use IGR-based baits (methoprene, pyriproxyfen) for slow but durable suppression; in commercial sites combine fast-acting metabolic baits with non-repellent perimeter sprays.

Sweet liquid bait at high volume around the perimeter and at every active trail, plus a non-repellent fipronil or thiamethoxam perimeter band. Liquid sucrose bait is the gold standard because of the species' dominant carbohydrate appetite. Successful programs maintain bait stations year-round.

Non-repellent perimeter spray plus sweet liquid baits is the operational standard. Inspect outdoors first, colonies almost always nest within 10–20 ft of the structure under mulch, landscape timbers, or in wall voids near plumbing. Apply sweet liquid bait at every active trail and refresh until trails disappear, then treat the structural perimeter with a non-repellent for residual control. Eliminate honeydew-producing aphids and scale on landscape plants near the foundation; this single step often collapses an infestation that resists indoor treatment.

• Amdro Pro Fire Ant Bait · Hydramethylnon 0.73%
• Extinguish Professional · (S)-Methoprene 0.5%
• Extinguish Plus · Hydramethylnon + Methoprene
• Advion Fire Ant Bait · Indoxacarb 0.045%

• Gourmet Liquid Ant Bait · Borate 1%
• Optigard Flex · Thiamethoxam 21.6%
• Termidor SC · Fipronil 9.1%
• Maxforce Quantum · Imidacloprid 0.03%

• Terro PCO Liquid Ant Bait · Borax 5.4%
• Advance 375A Select · Abamectin B1 0.011%
• Maxforce Quantum · Imidacloprid 0.03%
• Termidor SC · Fipronil 9.1%

Hot-water drench (3+ gallons at near-boiling, poured slowly into the mound center on a cool morning) kills roughly 60% of treated mounds and is the only practical option in organic settings; expect re-invasion. Excluding ants from electrical boxes with silicone sealant and gravel collars prevents shorts. Avoid disturbing mounds mechanically, colonies relocate within 24 hours and become harder to bait.

Manage honeydew-producing aphids, scale, and mealybugs on landscape plants, Argentine ant populations are limited by carbohydrate supply, and removing aphid colonies collapses local foraging pressure. Caulk utility penetrations, pull mulch away from foundation, fix irrigation leaks.

Caulk plumbing and wire penetrations, pull mulch back 12 in from foundations, trim shrubs and tree limbs off the structure, fix moisture leaks under sinks and around HVAC condensate lines, and store sugar / honey / syrup in sealed containers. ODH foraging collapses quickly once interior food and outdoor honeydew are denied.

Do not knock down or flood a mound before baiting, disturbed colonies stop foraging and reject bait. Do not water in granular baits; baits must remain dry and attractive. Do not treat one mound at a time on heavily infested ground; broadcast or you are subsidizing the survivors.

Pyrethroid-only perimeter applications fragment the colony and concentrate trails at the building. Bait alone cannot keep up with supercolony reinvasion; combine bait and non-repellent perimeter.

Do not spray trails with a repellent pyrethroid (bifenthrin, permethrin, cypermethrin), it fragments the colony and creates 3–5 satellite infestations from one. Do not rely on bait alone if outdoor honeydew is unmanaged; the colony will out-feed the bait.