Ants in a Willow Tree


We have a giant willow tree on our front lawn. It has been there 50 years. We like it because it gives our property character. We usually get it trimmed every 5 years. This year we noticed the bark was loosening in several places and ants were behind the bark when we tried to remove the bark. There are holes in the wood and what looks like sawdust at the bottom of the tree in several places. We think it might be carpenter ants but we are not sure. We read sprays might make it worse if we don’t get the queen ant.What should we do to remove these ants? We don’t want to loose the tree.



Your willow tree obviously gives you great pleasure.  Your first step should be to identify the ants.  Carpenter ants, which are typically about 6 to 25 mm in size, are very common in Ontario.  They are either “red”, with red and black bodies, or “black” carpenter ants, which are a dark brown-black all over.  In the mating part of their life cycle both males and females are winged.  The sawdust you describe at the bottom of the tree is typical of the way carpenter ants make their nests.  They do not eat live wood, but any holes in living trees are attractive to carpenter ants as nests.  It is worth mentioning that carpenter ants often form “satellite colonies” which could potentially include indoor nests in nearby buildings, so it is important that the perimeter of your house remains clear of any dead plant matter, old wood, or piles of firewood.

You mention that you have your tree trimmed every five years.  You may wish to consider calling your arborist to take a look, first to confirm that it is indeed a carpenter ant colony in your tree, and then to recommend a treatment.  To find a certified professional arborist to help you with a tree problem, visit the Ontario branch of the International Society of Arboriculture – trees are good

In your phone call, you asked about the use of diatomaceous earth, and this is indeed a possibility. For control of ants outdoors, the Ontario Ministry of Environment has approved the use of borax as well as diatomaceous earth.  Below is a link to a Gardening Guide on organic pest control for a more general discussion.

We wish you all the best of luck in preserving this venerable tree that has graced your front lawn for so many years.