There are several species of fire ants in the United States. The red imported fire ant, Solenopsis invicta (Buren), is the most widespread. It is also the most important species. It is common to find these fire ants. They have reddish heads and midsections with black abdomens.
In a colony of fire ants, there workers of different sizes. Scientists use the word polymorphic to describe the difference in the size of fire ant workers. Small workers, called minor workers, are usually less than 1/8″ long. The large workers, called major workers, can reach over ¼” in length. The queens are usually larger then the major workers. Fire ant queens can reach half an inch in length.
When scientists identify fire ants, they use a magnifying glass or a microscope. They examine the antennae, the midsection, and the number of teeth. Because fire ants bite and sting, it can be risky to get close enough to collect them or to examine them closely. Many people identify fire ants by observing their behavior.
Fire ants seem to prefer nesting in open, sunny areas. There can be hundreds of colonies of fire ants per acre. Workers will build a mound of soil, especially in cold or rainy weather. It is very common to find fire ant mounds beside sidewalks, driveways, and foundations. Fire ants also make their nests inside of wall voids and in electrical boxes.
Fire ants are very aggressive. If the mound is disturbed, hundreds of ants will rush out to defend the colony. They climb up onto the legs of the intruder. All of the ants seem to bite at the same time – as if they had heard a signal.
The ant workers can bite and then use their jaws to hang onto the skin of the victim. They rotate their abdomen and sting over and over. Fire ants got their name from these painful stings. In fact some people are sensitive to the venom and they become very sick if they are stung.
It is common for people to walk over small fire ant mounds without noticing them. This is the cause of many bites and stings. People who live in areas where fire ants are common supervise their children and pets closely when they are outdoors.