could be termites or carpenter ants...............try straight vinegar in the hole with a funnel....do it every day for 1 week.....about 2 cups................ That is the safest thing...but if you have children or pets you would have to keep them out of the yard and mix up Sevin according to directions. Pour it down the hole, make up a snall cone out of foil and then bag and trash it...I always use throw away gloves with chemicals with goggles & face mask.