By Laura Jesse
Iowa Sate University Plant and Insect Diagnostic Clinic
Have you ever been out digging in your garden and suddenly been surrounded by an odor of lemons? If so, you have probably disturbed a colony of larger yellow ants. When disturbed, ants commonly release a defensive compound that is irritating to predators and warns other members of the colony that there is a problem. In the case of larger yellow ants this compound smells to humans very much like citronella or lemon.
Larger yellow ant workers are about a quarter inch in length and very yellow in color. Larger yellow ants eat the honeydew of aphids and mealybugs feeding on the roots of plants. Honeydew is essentially the excrement of these pests that contains plant sugars and other nutrients. Larger yellow ants and many other ant species gather this honeydew, essentially treating the aphids like a herd of dairy cattle. Since larger yellow ants feed primarily below ground and their colonies are below ground, we seldom see them outside in our gardens.
However, larger yellow ants are encountered by many people in the late summer and fall when winged swarmers are produced. In an ant colony there are sterile female worker ants and the queen. An established colony will produce new queens and kings that will leave the colony to start new ones. These winged ants are called swarmers. The male swarmers, or kings, usually die after mating with the queens. The queen finds a suitable site to establish a colony, loses her wings and then begins laying eggs that will become her workers.
In the case of larger yellow ants, often the swarmers will stay with the colony through the winter and together the colony will move toward buildings and try to enter through cracks or gaps in the foundation. If the colony gains entry they will set up a temporary nest. The temporary indoor, winter nest is usually somewhere in the basement under a loose brick or board or in a crack in the wall or floor.
During the winter larger yellow ants do not forage for food through the house and apparently cause very little damage except to create piles of dirt at the entrance to the nest. Reportedly, these ants try to return to the outdoors sometime in the early spring if left undisturbed.
Control of larger yellow ants is not critical, since they cause little damage other than the annoyance of their presence. Ants found indoors in the winter can be vacuumed or swept up and discarded.
Concerned homeowners often fear that groups of larger yellow ant swarmers are termites. Termites also produce winged swarmers in a manner similar to ants. However, winged termites and winged ants can be differentiated. Ants and termites are actually not very closely related at all in the insect world. Termites are in a completely separate group and ants are more closely related to wasps and bees. Several characteristics are used to distinguish termites from winged ants. Ants have antennae with a bend, or elbow, and termites have straight antennae. Both ants and termites have four wings, but ants have different sized wings (the hindwings are smaller than the forewings) and termites have four wings that are the same size.
It is important to properly identify termites, so if you have any doubts about an insect identification please contact Laura Jesse at the Plant and Insect Diagnostic Clinic at Iowa State University. You can e-mail Jesse or call (515) 294-0581.