Fire ants (Solenopsis invicta) are recognized for their painful sting and the distinct mounds they construct. Understanding how to identify these insects and their nests is important for safety and effective management.
Recognizing the Ant Itself
Fire ant workers exhibit a range of sizes within the same colony, typically measuring between 1/16 and 1/4 inch (1.6 to 6.4 millimeters) in length. Their bodies are reddish-brown, often with a darker, shiny abdomen. This reddish coloration on the head and thorax, contrasting with a darker abdomen, is a key visual identifier.
Fire ants have a “waist,” or petiole, which consists of two segments or nodes connecting the thorax and abdomen. Their antennae have 10 segments, ending in a two-segmented club, and are bent at a 90-degree angle, or “elbowed”. They possess mandibles for grasping and cutting, and a stinger at the tip of their abdomen delivers painful venom.
Identifying Fire Ant Mounds
Fire ant mounds are a prominent sign of their presence and have several distinguishing characteristics. These mounds are typically dome-shaped and built from excavated soil, which often appears loose and fluffy. A key feature is the absence of a central opening on the surface, unlike many other ant species. Instead, the ants use underground tunnels for entry and exit, with openings often located at the base of the mound.
Fire ant mounds vary significantly in size, from a few inches tall in turfgrass to 18 inches (46 cm) high and 24 inches wide in undisturbed areas, sometimes reaching up to 1 meter in height and 1.5 meters in diameter. These mounds are frequently found in sunny, open areas such as lawns, fields, and along sidewalks. Mounds may appear or become more noticeable after rainfall, as the softened soil makes it easier for the ants to dig. They can also be located under objects like logs, rocks, or inside electrical boxes. Internally, the nests consist of many interconnecting galleries, giving them a honeycomb appearance.
Distinguishing Fire Ants from Similar Species
Differentiating fire ants from other ant species is important for accurate identification. One key physical difference lies in the petiole, or waist. Fire ants consistently have two nodes on their petiole. In contrast, some native red ants may have only one node. Pavement ants, another common species, also have two nodes but are typically dark brown to black, with stiff hairs and distinctive grooves on their head and thorax. Odorous house ants are uniformly brown to blackish-brown, have a single, often hidden, node, and release a rotten coconut-like smell when crushed.
Behavioral cues also provide indicators for identification. Fire ants are aggressive and will swarm rapidly out of their mounds, attacking in large numbers when disturbed. They tend to climb vertical surfaces, such as grass blades or human legs, to sting. This aggressive swarming behavior and their painful, burning sting, which can result in white, fluid-filled pustules, are distinctive to fire ants. Other ant species, like pavement ants, are generally less aggressive and do not exhibit the same rapid swarming or painful stinging response.