WSU Extension

Pestsense

Caption: European Fire Ant
Photo by: www.antweb.org
  
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European fire ant

(revision date: 4/21/2021)


Use Integrated Pest Management (IPM) for successful pest management.

Biology
The European fire ant (Myrmica rubra), sometimes known as the red ant or ruby ant, is a native of Europe and Asia. It has been present in the northeastern United States and neighboring Canadian provinces for many years, and has also been found recently in Washington State and British Columbia. While its occurrence in the Pacific Northwest is relatively isolated for now, it has great potential to spread and become a significant pest in our area. European fire ant (EFA) workers are reddish-brown ants about 1/5 inch long. However, color can vary greatly between individuals and between colonies. The body is covered with fine hairs. The head and thorax are sculpted with ridges and grooves and appear somewhat dull, while the abdomen is shiny. EFA workers have two backward-pointing spines on the back of the thorax and a distinct, two-segmented pedicel or “waist.” This species does not build obvious mounds or hills. They like high humidity so will often build in soil at the base of trees or shrubs, under rocks or logs, or in similar sheltered or shady areas. Some colonies have been reported to move nests regularly during the summer. EFA colonies contain multiple queens and may spread into adjacent areas by “budding” (forming satellite colonies of a queen and a group of workers). They are typically spread by transport of infested container plants, soil, or mulch. EFA is considered a potentially significant pest species due to the highly aggressive nature of the workers, the high population density in infested areas, and its fondness for nesting in areas also enjoyed by humans. EFA workers can deliver a painful sting which may cause severe allergic reaction including anaphylactic shock in sensitive individuals. In addition to human impact, these ants will also have an effect on the ecology of the areas they invade, both by impacting native species and by their habit of tending and protecting aphids and other honeydew-producing plant pests. European fire ant should not be confused with the two imported fire ant species (Solenopsis spp.) that are a problem in the southern United States. For assistance identifying suspected EFA specimens, contact your local Extension office.
Management Options

Non-Chemical Management
  • Native Myrmica species in Washington closely resemble EFA in appearance, but occur in low numbers and are not considered aggressive. For assistance with accurate identification of ants, contact your local Extension office.
  • Prevent spread of this invasive species. Do not transport soil, potted plants, or mulch from known infested areas. Inspect plants, soils, and mulches before use.
  • Reduce irrigation, mow tall grasses, and increase sun exposure to the soil to make the environment less hospitable to these ants. Remove debris including rocks, boards, logs, etc. to reduce desirable nesting sites. These tactics will not eliminate colonies, but may help to keep populations low.
  • Control populations of honeydew-producing insect (aphids, scales, etc.) to make your landscape less attractive to EFA.
Select non-chemical management options as your first choice!

Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

The efficacy of bait products against EFA is currently under evaluation. While these ants are attracted to carbohydrates (sugar, honey, etc.), results using food-based baits have been inconsistent. Hydramethylnon-based baits are reported to have some efficacy but have not been tested specifically against EFA. Based on research done in the Northeastern United States, bait products are most effective during early to mid-summer, when colonies are consuming the most food. This research also indicates that repeat chemical applications may cause colonies to relocate. It is not known how EFA in Washington will react to chemical applications. These products may not provide complete control, but should reduce numbers. May require two applications.

If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
  • Amdro Kills Ants Ant Killing Bait
    Active ingredient: hydramethylnon  |  EPA reg no: 1663-33-73342
  • Combat Outdoor Ant Killing Granules
    Active ingredient: hydramethylnon  |  EPA reg no: 64240-25
  • This list may not include all products registered for this use.
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Caption: European Fire Ant
Photo by: www.antweb.org
Caption: European Fire Ant
Photo by: A. Nobile, www.antweb.org