Current Issue

Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

In a warming world, here comes the red imported fire ant, Solenopsis invicata


The range of fire ants in the U.S. is predicted to spread. (Image from USDA – ARS)


Soaring temperatures last week in the Washington area were a reminder of our warming world. One of the consequences of climate change is an expansion of the geographic range of some southern species of insects into northern zones where cold winter temperatures once excluded them. One such range expansion appears to be underway for the red imported fire ant; a denizen of the south that appears with increasing regularity in the north. Where did this fierce insect originate? In the 1930’s a South American freighter docked in Mobile, Alabama with more than cargo on board. Somewhere in the ship, probably in the ballast, a queen and her court waited to disembark into a new land. The red imported fire arrived by sea, escaped, and now occupies more than 300 million acres of land in the gulf coast states and as far north as Virginia, Tennessee, Arkansas, and Oklahoma. This pernicious insect also infests portions of New Mexico and California.

Local infestations have been found in Maryland, but it is still not clear how long these colonies can persist in northern climes. Several years ago I discovered a colony of fire ants in a landscape bed outside of a bank in Columbia, MD. Another colony was found on the University of Maryland Campus a few summers later. Frequently, my friends at the Maryland Department of Agriculture report infestations in landscapes associated with restaurants that installed tropical potted plants imported from the quarantine zone in the South.

One day after being stung, a small itchy welt appeared on my finger.

Those who have not encountered fire ants might be thinking antz schmantz – what’s the big deal? My first serious encounter with fire ants happened on a bug-collecting trip in Florida. I was squirming through vegetation and stopped to photograph a dragonfly. I knelt in a fire ant nest and within seconds my right leg was covered with dozens of stinging, biting ants. The sting of a fire ant is unique, something less than the bite of a Doberman, but more than that of a mosquito. The defending ant grasps the skin with powerful jaws. She curls her abdomen beneath and stabs the flesh of the adversary with a stinger injecting potent venom that burns like fire for several minutes. She can administer several stings until forcibly removed or crushed.

Three days after a fire ant attack my leg was still red and itchy.

The normal reaction to one or a few bites will be several minutes of memorable pain followed by a small raised pustule. This blister may turn whitish or red. Beginning the day after the attack, my welts itched periodically for several days. As long as the welts do not become infected, which usually occurs when welts are scratched and secondary bacteria are introduced, the associated redness disappears in less than a week. However, for a small fraction of people, one to five percent, a fire ant sting can be more dangerous. Several years ago an elderly women in South Carolina died after being stung by fire ants while she was gardening. Following a sting, people allergic to fire ants may have symptoms including itching and hives over much of the body, upset stomach and cramps, swelling of the tongue and throat, headache, tightness in the chest, difficulty breathing, disorientation, and loss of consciousness. Anyone experiencing these symptoms following the sting of a fire ant or any stinging insect such as a bee or wasp should seek medical attention immediately. People with known allergies to insect stings should be especially careful when visiting locations infested with fire ants because there may be cross sensitivity to fire ant allergens and those of other stinging insects.

Fire ants are not readily distinguishable from many other ant species. They typically have a reddish-brown head and thorax with a dark abdomen, or may be all-over dark in color. They are not fiery red as suggested by their name. They are variable in size, ranging from very small to moderately sized, about 1/16 to ¼ inches. While it might be difficult to distinguish a fire ant from other less noxious ants crawling side by side on the pavement, their behavior and nests are dead giveaways. Fire ants build colonies in the ground that may be several feet in diameter and more than two feet in height. A single large fire ant mound will contain dozens of queens each capable of laying more than 1000 eggs per day. Colonies may contain more than a quarter of a million ants. These are ants with an attitude. Workers are highly aggressive when a predator or a bug geek’s finger threatens the colony. Defenders swarm onto the intruder in seconds and begin a mass attack.



When the nest is disturbed, legions of fierce stinging workers will defend the colony to their death.

To avoid fire ant stings avoid the ants, learn what mounds look like and stay clear of them. Teach children to recognize and avoid them. Inspect picnic areas including tables and benches as well as lawn areas before using them. If you live in an infested area, wear closed shoes rather than sandals while gardening. Tuck your pant legs into your socks to prevent ants from moving beneath clothing and up your legs to sting. Colonies can be eliminated by treating them with very hot water or potent insecticides applied as granules or drenches. Professional pest control operators have the skill and tools to eliminate infestations. Recently, a remarkable fly has been imported and released in the South as a biological control agent for fire ants. The female fly pierces the body of the ant and deposits an egg inside. The egg hatches into a maggot that eats the entrails of the fire ant and works its way to the victim’s head. The maggot consumes the tissue connecting the ant’s head to its thorax decapitating the ant in the process. Sweet!

If you live in areas outside of the zone of known infestations, and you believe that you have found a fire ant colony, please contact the officials at your state Department of Agriculture. So, while we revel in the warmth of December days rising into the 70s, be aware of bevies of southern bugs that will soon be taking up residence in the north.



Ouch! That hurts!


The fascinating study “Zombie fire ant workers: behavior controlled by decapitating fly parasitoids” by D. Henne and S. Johnson was consulted to prepare this episode. To learn more about fire ants and their stings, please visit the following web sites: ants&kt=&kid=&pid=