Gary Alpert, Harvard University, Bugwood.org
Lasius interjectus, the larger yellow ant and Lasius claviger, the smaller yellow ant
The citronella ants get their name from the lemon verbena or citronella odor they emit when threatened. It is most noticeable when the ants are crushed. They are subterranean insects that feed on the honeydew (excretions) of aphids and mealybugs feeding on the roots of shrubs.
Both the larger and the smaller yellow ant are found throughout much of the continental United States. They are very common in the eastern United States and are frequently confused with termites when they swarm into the living areas of homes. In both species, the swarmers (winged ants) may vary in color from the more common light yellow to a dark reddish-yellow or light brown. The workers are typically yellow with less color variation than the swarmers.
Of the two species, the larger yellow ant (L. interjectus) is the most commonly encountered in Pennsylvania homes (Fig. 1). The workers are 4 to 4.5 mm long and have 12-segmented antennae, with the scape (first antennal segment) just reaching the top of the head. They have a single node to the pedicel connecting the thorax and abdomen, with sparse, erect hairs on the head, thorax, and abdomen.
The swarmers are approximately twice the size of the workers and have dark, smoke-colored wings. Like the workers, they can also vary in color from a light yellow to light reddish-brown.
Other than its size (workers are 3 to 4 mm), the smaller yellow ant looks similar to the larger yellow ant.
Fig. 1. Citronella ant
Little is known about the inner workings of these subterranean colonies. The ants are believed to tend aphids (much as dairy farmers would cows) and collect the honeydew they excrete. They are not known to forage for other food sources. Nest sites may include open woods, pastures and fallow fields, gardens, lawns, and next to house foundations. Also, some colonies are located beneath concrete slabs and large rocks, and in and beneath rotting logs.
Swarms may occur in and around homes any time of the year. The most common swarming occurs in mid- to late summer, but swarmers have been collected from homes during late autumn and early spring. These early and late season swarms are possibly an abnormality created by the warmer soils under and adjacent to heated structures.
Citronella ants should be considered only as a nuisance pest species. Normally, they go unnoticed unless the swarmers enter through expansion cracks in slabs or around door openings. Although these intrusions may alarm homeowners, the ants will not reproduce within the home nor will they attack stored goods or structures.
In some cases, swarms may occur repeatedly and attempts should be made to locate the colony or colonies. Colonies typically have mounds of soil around the openings where excavated soil is deposited. These mounds can be treated by injecting an insecticide into the holes. Although numerous insecticides are labeled for ant control, many of these can only be used by licensed individuals. Therefore, a professional pest control company should be contacted because they can use materials not available to the general public and have access to specialized application equipment.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Steve Jacobs Sr. Extension Associate
Revised January 2014