Fire ants are an invasive species known for their aggressive behavior and painful stings. They can significantly impact ecosystems, agriculture, and public health. Understanding their characteristics and distribution is important for residents in areas where they might appear.
The Current Situation in Wisconsin
Established populations of imported fire ants, including Red Imported Fire Ants (Solenopsis invicta) and Black Imported Fire Ants (Solenopsis richteri), are generally not found in Wisconsin. The state’s colder climate acts as a natural barrier, preventing these species from establishing widespread colonies. While individual ants or small colonies might be inadvertently transported into the state, often via nursery stock, they usually do not survive the harsh winter. These introductions are isolated and do not lead to reproducing populations.
Key Characteristics of Fire Ants
Fire ants have distinct physical and behavioral traits. They typically have a reddish-brown coloration with a darker abdomen. Worker ants within a single colony vary in size, ranging from 2 to 6 millimeters (1/16 to 1/4 inch) in length. This size variation helps differentiate them from other ant species.
When disturbed, fire ants exhibit aggressive swarming behavior. They bite, then sting repeatedly, injecting a toxic alkaloid venom. The venom causes a burning sensation and forms itchy, pus-filled blisters, diagnostic of a fire ant sting. Their characteristic dome-shaped mounds, often asymmetrical and lacking a central opening, also identify colonies.
Common Wisconsin Ants Often Confused with Fire Ants
Many native Wisconsin ant species are mistaken for fire ants due to similarities in appearance or mound-building habits. Pavement ants (Tetramorium immigrans) are small, dark brown to black ants that commonly nest under sidewalks and driveways, creating small soil mounds. While they can sting, their sting is less painful than a fire ant’s, and they lack the distinct reddish coloration of true fire ants.
Field ants (Formica species) are another common group in Wisconsin, some of which can be reddish or red and black. These ants build large mounds, sometimes several feet wide and over two feet tall, which might be confused with fire ant mounds. However, field ants typically bite and may spray formic acid, causing a burning sensation, rather than delivering a venomous sting that results in pustules. Carpenter ants, some of which can be red or reddish-brown, are also larger than fire ants and do not sting, but rather bite.
Reporting Suspected Fire Ant Sightings
Report suspected fire ant sightings in Wisconsin to the appropriate authorities for identification. Avoid disturbing the ants or their mounds, as this can provoke aggressive stinging. Contact the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) through their Pest Hotline at (866) 440-7523 or by emailing photos and your location to [email protected].
Clear photographs of the ants and their mound are helpful for identification. You can also contact a local university extension office, such as the University of Wisconsin-Madison Department of Entomology or their Insect Diagnostic Lab, for assistance. Early reporting helps state agencies monitor and respond to invasive species threats.