Red Ants Vs. Black Ants
To distinguish aggressive red fire ants from other types of ants, consider their physical shape, their nesting habits and the way they behave.
Some people view world issues simplistically, seeing everything in terms of black and white. It's equally easy to view the ant kingdom simplistically -- in terms of red and black. The general line goes like this: Black ants are harmless, red ones aggressive and dangerous. But the truth is more nuanced, and the color alone is not enough of an identification.
Red, imported fire ants are the stinging, aggressive ants people refer to as "red ants." Black ants include common ants like the pavement ant, Tetramorium caespitum, the black carpenter ant, Camponotus pennsylvanicus, and the little black ant, Monomorium minimum. But some ants that fall within the category "black ants" (including carpenter ants, pavement ants and field ants) are not black at all. Some are a reddish brown color, and others can be yellow, orange or greenish. For this reason, it's more useful to compare fire ants to other ants than red ants to black ants. Here's how you can figure out whether reddish-colored ants are invasive fire ants.
What Do Fire Ants Look Like?
You can distinguish red fire ants from other ants by their physical appearance. Look carefully at an ant you wish to identify, and how its body is constructed. All insects have three distinct body regions: the head, thorax and abdomen. The regions are united by different segments, termed "nodes."
Red, imported fire ants are a reddish brown, with the abdomen darker than the rest of the body. They have two nodes at their waist between the thorax, in front of the nodes, and the abdomen, at the back. The heads will never be wider than the abdomens. Look at the antennas on the head. Fire ant antennas have 10 different segments with a club of two segments.
Size varies from 1.5 mm to 4 mm. That means they are very small, with the largest ones topping out at about 1/10 of an inch long.
Where Ants Live
Another way to distinguish fire ants from other ants is by their living arrangements. So-called black ants live in different areas depending on their species. Pavement ants and little black ants nest under structures, sidewalks and foundations. Black carpenter ant build nests in decaying wood.
Fire ants build tunnels and chambers underground. They live in these chambers until it is time to breed, usually in spring, fall or after a period of cool wet weather.
At that point, when conditions are good for breeding, fire ants expand their nests above the ground with lose, crumbly soil. These above-ground nests look a little like dirt piles left by gophers, and normally are about 18 inches in diameter. You'll find them in open, sunny locations. What you won't see is an entrance. Red imported fire ant mounds do not have an entrance in the center of the mound.
How Fire Ants Behave
While the black ants you find in your kitchen are fairly docile, simply looking for food to take back to the nest, fire ants are hotheads. Watching their aggressive behavior is another way to confirm their identity.
If someone roughs up a fire ant nest, the red ants don't scuttle off to escape or rush in to try to save their larva. Instead, they come swarming out immediately, ready to fight. They defend their nests aggressively, often climbing up vertical surfaces, including the legs of people or animals, to be in a better position to attack.
Perhaps the absolute way to confirm that the red ants you are looking at are fire ants is when you get stung. Fire ants are unique in that they are the only ants to grab onto their "prey" with their mouths and hold tight while they inject toxins. The burning pain at the sting is intense and painful. These aggressive ants attack small animals like quail, songbirds, lizards and frogs. If an ant sting causes an intense burning sensation, it's probably a fire ant. The pain doesn't go away quickly, and after about four weeks, the sting sites forms white pustules.