The invasive Red Imported Fire Ant (Solenopsis invicta) is not established in Michigan. While this species is a significant pest in the Southern United States, it has not gained a permanent foothold in Michigan’s ecosystem. Occasional, isolated sightings are possible, as they can hitchhike on soil, potted plants, or nursery stock transported from infested regions. However, these transient occurrences are rare and do not indicate a breeding, established population.
Current Status and Climatic Barriers
Fire ants are not widespread in Michigan because the region’s climate acts as a natural barrier to long-term establishment. The established range of S. invicta is primarily limited to the deep South and Southeast, including states like Texas, Florida, and Alabama. Michigan falls far outside this zone necessary for the ant’s survival and reproduction.
The northward spread of these ants is limited by cold temperatures. Fire ant colonies cannot survive where the minimum winter soil temperature consistently drops below a certain threshold. Researchers predict the species is unlikely to colonize areas that experience minimum temperatures below -3.7 °C (25.3 °F), a temperature Michigan regularly reaches. The state’s prolonged, freezing winters prevent the colony from surviving deep in the soil, successfully protecting the region from widespread infestation.
Key Characteristics of Fire Ants
Identifying the Red Imported Fire Ant requires observing several unique features. They are polymorphic, meaning workers within a single colony vary significantly in size, ranging from about 1/16 of an inch to nearly a quarter of an inch long. This size variation is a rare characteristic among ant species. Their coloration is a reddish-brown on the head and thorax, with a darker, sometimes black, abdomen.
The ant’s body structure includes a petiole, the narrow “waist” connecting the thorax and abdomen, which has two distinct segments or nodes in S. invicta. A telltale sign of a fire ant colony is the mound it constructs, which is typically dome-shaped and lacks a central entrance hole. Unlike many native ant species, fire ants enter and exit their nest through underground tunnels, leaving the soil mound smooth and undisturbed until it is breached.
Michigan Ants Commonly Mistaken for Fire Ants
Many native Michigan ant species are commonly mistaken for the invasive fire ant because they build soil mounds or have a reddish appearance. The Allegheny Mound Ant (Formica exsectoides) often creates large soil mounds several feet in height, typically found in open, sunny areas. These ants are brick-red and black, but they are significantly larger than fire ants. They are known for biting and spraying formic acid, not stinging like S. invicta.
Another common misidentification is the Pavement Ant (Tetramorium immigrans), which is small and dark brown to black, often found nesting in cracks in sidewalks and driveways. Pavement ants are smaller than the largest fire ant workers, and their workers are uniform in size, unlike the polymorphic fire ant. Pavement Ants create small, crater-like mounds with a visible central opening, a feature absent from fire ant mounds.
What to Do If You Find a Suspected Fire Ant
If a Michigan resident suspects they have found a Red Imported Fire Ant, the first step is to avoid disturbing the colony. Disturbing the mound will cause the ants to swarm aggressively and sting, so observation should be from a distance. Safely collect a specimen or take clear photographs, placing the specimen in a sealed container filled with rubbing alcohol for preservation and identification.
The proper authority to contact for verification is the Michigan Department of Agriculture and Rural Development (MDARD). Suspected invasive species sightings should be reported to MDARD through the Michigan Invasive Species website or hotline. Rapid reporting allows state officials to investigate the sighting, confirm the species, and quickly implement a containment plan to prevent any potential establishment.