Managing Household Ants - August 12, 2015
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

In our gardens, ants are often found tending aphids, scales, whiteflies, and mealybugs while harvesting their honeydew (the sweet, sticky substance they secrete). Some species, including carpenter ants, destroy wood and/or collect plant litter. Others invade our homes and live off our food and crumbs. There are over 12,000 species of ants throughout the world. To narrow the field, this column will focus on household ants: in particular, the odorous house ant (Tapinoma sessile).

Ants, like their relatives, bees and wasps, are social insects that go through stages of complete metamorphosis: egg, larva, pupa, adult. Larvae are immobile and wormlike and do not resemble adults. Ants, like many other hymenopterans, are social insects with duties divided among different types, or castes, of adult individuals. Queen ants are the largest in the colony and lay the eggs and sometimes feed and groom the larvae. Sterile female workers gather food, tend the larvae, build tunnels, defend the colony, and are the most numerous within the colony. Male ants do not participate in colony activities and their only apparent purpose is to mate with the queens. The males are fed and tended to by the female workers.

A single, newly mated queen typically establishes the colony. She lays eggs, feeding the hatched larvae her own metabolized wing muscles and fat bodies until they pupate. Several weeks later, the pupae transform into sterile female adult workers, and the first workers dig their way out of the nest to collect food for themselves, for the queen (who continues to lay eggs), and for subsequent broods of larvae. As numbers increase, new chambers and galleries are added to the nest. After a few years, the colony begins to produce winged male and female ants, which leave the nest to mate and form new colonies.

Odorous house ants are 1/8" to 1/4" inch long, blackish, brown in color, and often invade a home by the thousands following a change in the weather. They also have a distinct smell when crushed that some people say is similar to rotten coconut. Odorous house ants often have their nest outside of your house near a shrub or mulched area and enter through a crack in the wall, window, or foundation. Indoors, nests can be found in wall voids, around hot-water pipes and heaters, behind paneling, carpets or beneath the floor. They typically feed on sweets, vegetables, meats, and dead insects.

Scout ants (female workers) wander in search of food. Once food is located, she takes a short, direct route home. While returning, she also leaves an odor trail. Upon reaching the nest, she alerts her nest mates of the food source and they all follow the odor trail directly to the food source. This phenomenon is called trailing. Trailing ants can be closely observed and this behavior can be exploited in their control.

The foremost management strategy should be sanitation. Remove potential food sources by promptly wiping up spills and storing foods in sealed containers. Exclusion is your second line of defense. Follow the trail location and seal the cracks, caulk the seams, and use other materials to limit their entry. This is easier said than done due to the small size of this pest and their large numbers. Next, scrub trails with detergent to remove the scent (pheromone) trail.

Preventative measures are not always 100% effective and insecticide treatment may be necessary. Toxic baits are preferred because the ants transport the insecticide to the nest. The toxins in the baits range from environmentally friendly boric acid to synthetic insecticides. The bait itself can be tricky too. Ants have varied diets that may or may not include sugars, fats, and proteins depending on the state of the brood and other colony needs. To bait successfully, the toxin must be transported back to the colony and ingested by the queen as well as the others. If toxic baits are used, do not use insecticide sprays. This will not allow effective transport of the toxin back to the colony. Follow label directions on any products you decide to use. Additional ant management information is included below.

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Additional Resources

Ants in the Home
Colorado State University Extension

Ant Managemnt Guidelines
University of California Agriculture and Natural Resources

Identifying Household Ants
Texas A & M Agrilife Extension

What to do if you have an ant emergency, University of California Agriculture and Natural Resources.

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: August 3, 2015
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