Thatching ants are large red-and-black mound-building ants common in open, wooded areas of Whidbey and Fidalgo. They build thatch mounds of grass and twigs, defend them aggressively, and can bite and spray formic acid.
How to identify thatching ants
Workers are 1/4 to 3/8 inch, red and black, with a notched, saddle-shaped thorax. They build distinctive dome mounds of plant debris.
Behavior & season on Whidbey & Fidalgo
They nest outdoors in sunny, open ground and forage on insects and honeydew. Colonies are most active in warm months and vigorously defend the mound when disturbed.
Why thatching ants are a problem
They rarely enter structures but their large mounds and aggressive, acid-spraying bites make yards, gardens, and play areas unpleasant, and they protect aphids that damage plants.
Signs of thatching ants activity
- Dome-shaped mounds of grass and twigs
- Large red-and-black ants defending the mound
- Painful bites when the nest is disturbed
- Aphid activity on nearby plants
How Salty Dog treats thatching ants
We treat the mound directly and manage the surrounding foraging area so the yard is usable again, keeping treatment away from non-target areas. Learn more about our Outdoor Pest Control service, or browse the full Pest Library.
Reviewed by Matthew — Salty Dog Pest Control. WSDA-licensed structural pest applicator (License #101709). Veteran- and family-owned, serving Whidbey Island, Fidalgo Island, and west Skagit County.
Frequently asked questions
Are thatching ants dangerous?
Their bite is painful and they can spray formic acid, but they are not a structural or serious health threat — mainly a yard nuisance.
Should I knock the mound down?
No — disturbing it provokes defensive swarming and does not eliminate the colony. Targeted treatment is safer and more effective.
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