I had the same problem when ants nested under the styrofoam filled seats of my little Jon boat!
I used two cans of Raid and thought I had killed them all. Two weeks later we were on the lake and they swarmed out all over us!
Beat it to shore and they were in our clothing, biting like crazy. Luckily no one was at the refuge ramp and grandson and I stripped down and hit the water. We got multiple bites.
These were fire ants that got in my boat. I stayed with the Raid for two weeks, spraying every morning. The boat is "ant free" now.
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****Sun sinking low....lines baited.....gentle south breeze blowing...you realize.........I AM! .