Argentine ants are on the rise


April 3, 2003

By: Austin Frishman

The Argentine ant (Linepithema humile) has been in the United States for more than 100 years. For the last 15 years or so, though, this Brazilian import is fast becoming a major pest — particularly in California, Hawaii and the Southeast.

Once present, they waste no time in significantly increasing callbacks. To better understand these ants means to have a better chance in controlling them. Here are some facts about this species:

1 They can rapidly relocate a nest — The type of location they nest in is so variable that almost anything goes. For example: empty soda cans held for recycling, backyard fruit trees, hummingbird feeders, buses, cars and other vehicles, potted plants and roofs. You may never find all the nesting sites.

2 After heavy rains, they enter buildings in huge numbers — You can expect increased customer calls, so let your office staff know ahead of time what might happen.

3 Aphids provide honeydew, a major food source — Controlling aphids can help control the ants, as well as increase the efficacy of carbohydrate-based baits.

4 They are polygynous — This means many queens are present in one nest. With baits, you get one queen at a time. You can wipe out 99% of the colony and they can still rebound.

5 They are polydomous — This means many nests are present in a single colony. The greater the area the nests cover, the more difficult control becomes.

6 Temperature influences foraging behavior — The ants stop foraging above 86° F. Baits will not work well during the heat of a summer day. The ants may try to beat the heat by moving about and feeding under the mulch. Consider baiting under the mulch inside ant or rodent bait stations.

7 They travel along edges of surfaces such as asphalt and wood — Look for such areas when deciding where to bait.

8 They are strong pheromone trail creatures — You can predict where the ants will be night after night and day after day.

9 They do not sting or bite — This helps diffuse customer apprehension, and they can tolerate them a little longer than say, fire ants.

10 They consistently rank in the top 5 hard-to-control ant species — You have to work to get control. Charge accordingly.

11 They feed on wounds and can enter ears and noses of people sleeping — Do not take this ant lightly. Set up perimeter barriers to keep them away from a structure.

12 As a colony, they eat a lot — Small ant bait stations are not enough. Several large ones may be required. The first time you bait, come back after a few days to see whether more bait is needed.

13 The ants can use shrubbery and small cracks to reach a structure — Trim shrubbery so it does not touch the structure, and seal cracks.

14 They drive out native ants that are needed as food for reptiles, some of which may be endangered — It is environmentally sound to control the Argentine ants in order to maintain the balance of nature.

15 They are highly repelled by pyrethroids — If the ants are already in a building and you place a pyrethroid residual on the exterior, you can end up locking the ants inside. They scatter, and sightings increase.

16 Large potted plants can provide a “Trojan horse” strategy in sneaking whole colonies in a building —Have all potted plants checked before they are brought into a building.

17 The ants go for moisture in walls — Use a moisture meter to check walls. If a problem is found, mark with a UV pen and on the next inspection, check with a black light. Read the moisture meter again. Check that the sprinkler system on the exterior is not hitting the walls.

18 Once you eliminate a colony, a new one may re-enter the area within days or weeks — There is a need for ongoing pest control. Keep a close watch on the exterior of the property, and keep fresh baits available. PC


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