Large Yellow Ant

Description: The most common species, the larger yellow ant is sometimes called “citronella ant”. These ants have a distinct lemony smell when they are crushed. In the Northwest, these ants nest in structural areas where there is high moisture content; hence the common name, moisture ant. They are large ants ranging from 1/4 to 3/16 inch long. They are pale yellow to yellow-red and have a single node in their petioles and a circle of hairs at the tip if the abdomen.

Biology: Very little is known about the biology of these ants. The large winged reproductives develop in the fall and overwinter, emerging in swarms, often by the thousands, in the early spring through early fall. They often emerge into structures (particularly heated basements) causing the occupants to misidentify them as termites because of their size and their appearance during termite swarming season.

Habits: Large yellow ants nest in rotting wood, in the soil, and in the foundations of homes. Indoors they are found in the crawlspace soil, between insulation and subflooring, patio stones, rocks, landscape timbers, etc. These ants tend to excavate large galleries and stack up large amounts of soil adjacent to the nesting site. In some parts of the country, multiple small openings (mounds) may appear throughout the lawn.

They feed exclusively on honeydew obtained from the aphids they tend on plants. Because yellow ants forage at night, they are seldom seen in structures by customers and perhaps this explains why they have never been reported feeding on human food.

Control: If they are nesting in moist wood in the structure, the moisture source should be eliminated and the wood dried. Rotting firewood that is serving as a nesting site should be removed. These ants are seldom of concern in structures except when the swarmers emerge. Swarmer are best removed using a vacuum cleaner. After collection, the vacuum bag should be sealed and discarded. If this is not practical, a nonresidual aerosol should be used to knockdown the swarmers. Nests located in or around structures should be drenched with a liquid residual product. Baits are ineffective in controlling these ants.

Controlling aphids on ornamental plants and trees around structures removes their primary food source and causes them to forage elsewhere for food.