A Walk with The Arborist: Arbor Dogs and Ants
Updated: Oct 2
Carpenter Ants and Hidden Tree Decay: What a Fallen Pine Can Reveal
During a recent filming of “Walk With the Arborist” at Bullard Farm, Scott—and the arbor dog—stopped to inspect a fallen pine tree. From the outside, the tree may not have shown any obvious signs of trouble. Once it failed, however, the broken trunk revealed extensive internal decay and galleries excavated by carpenter ants.
The discovery offers an important lesson for property owners: sometimes the most significant structural problems are hidden inside a tree. Carpenter ants may provide a clue, but they are usually only one part of a much longer story.
Carpenter Ants Are Not Termites
Carpenter ants are often blamed for destroying trees, but they behave differently from termites. They do not consume wood for food. Instead, they remove pieces of wood to create galleries where the colony can live and raise its young.
These ants are especially attracted to damp, softened, or decaying wood because it is easier to excavate. A colony may live inside a standing tree, fallen log, stump, or dead limb. Carpenter ants can also occupy the decayed interior of an otherwise living tree.
As Scott explains in the video, the ants visible inside this pine had carved through wood that was already dead or deteriorating. Their presence was more likely evidence of an existing problem than the original reason the tree declined.
Which Came First: The Ants or the Decay?
In most cases, decay begins before carpenter ants establish a colony. A tree may first be injured by a broken limb, trunk wound, crack, root damage, or another opening that exposes interior wood. Moisture and wood-decay fungi can then begin breaking down the affected tissue.
Once the wood becomes moist and soft, carpenter ants may move in and enlarge the existing spaces. Their tunneling can contribute to the loss of already weakened wood, but eliminating the ants does not repair the underlying decay.
This is why treating the ants alone may not solve the actual tree problem. The more important question is why the wood became suitable for them in the first place—and how much structurally sound wood remains.
When a Healthy-Looking Tree Has a Hidden Problem
The pine at Bullard Farm illustrates how internal decay can remain concealed. A tree may retain normal foliage and continue growing even while part of its trunk or root system deteriorates internally.
Much of a tree’s active system is located in the outer portions of its trunk. These layers can continue transporting water and nutrients while the older wood toward the center loses strength. As a result, the canopy may look healthy even though the tree’s structural support has been reduced.
Eventually, wind, wet snow, ice, or the weight of the tree itself may place more force on the weakened area than it can withstand. What appears to be a sudden failure may actually be the final stage of a process that has been developing for years.
Are Hollow Trees Always Dangerous?
A hollow or cavity deserves attention, but it does not automatically mean a tree will fail or must be removed. Some hollow trees remain standing for many years and continue producing healthy growth. In natural areas, cavities and decaying wood also provide valuable habitat for insects, birds, and other wildlife.
The structural significance of a hollow depends on several factors, including its size and location, the amount and distribution of sound wood surrounding it, the condition of the roots and canopy, and the tree’s exposure to wind.
Location also matters. A decaying tree deep in the woods presents a very different concern from a similar tree beside a home, driveway, playground, or frequently used outdoor area.
How Arborists Investigate Internal Decay
An arborist generally begins with a visual inspection of the tree and its surroundings. Cavities, cracks, seams, fungal growth, carpenter ant activity, loose bark, dead branches, or changes in the tree’s lean may indicate that closer investigation is warranted.
One basic assessment method is called sounding. An arborist taps the trunk with a mallet and listens for differences in tone. Sound wood generally produces a different response than wood surrounding a hollow or advanced decay.
When more information is needed, an arborist may recommend advanced testing. A resistance-recording drill can measure changes in wood density along a very narrow path. Sonic tomography uses sound waves to help create an image of the wood inside a trunk.
These tools require experience to use and interpret correctly. Drilling into a tree should not be treated as a casual homeowner test because unnecessary drilling creates wounds and only provides information about the particular path tested.
Warning Signs Property Owners May Notice
Although internal decay can be difficult to detect, property owners can watch for possible warning signs. These may include:
Carpenter ants repeatedly entering or leaving the same opening
Coarse sawdust or wood shavings collecting near the trunk
Visible hollows or cavities
Cracks, splits, or seams in the trunk
Mushrooms or fungal growth near the trunk or roots
Dead or broken branches in the canopy
A sudden change in the tree’s lean
Soil lifting or cracking around the root system
None of these signs provides a complete diagnosis by itself. They are reasons to look more closely and, particularly when the tree could reach people or property, consider arranging a professional evaluation.
A Fallen Tree in the Forest Versus a Tree in Your Yard
As Scott notes, tree failure is a normal part of the forest. Trees decline, fall, and decompose, returning nutrients to the soil while creating habitat for other organisms. Carpenter ants and other decomposers participate in this natural cycle.
The circumstances change when a tree grows in a residential or commercial landscape. A tree near a building, road, parking area, or gathering space has potential targets if it fails. That does not necessarily mean the tree should be removed, but it does make understanding its condition more important.
Tree risk is not determined by a defect alone. An arborist also considers the likelihood of failure, what the tree or branch could strike, and the potential consequences.
The Lesson Inside the Fallen Pine
The broken pine at Bullard Farm reveals something its exterior may have hidden: a hollowed and decaying interior occupied by carpenter ants. The ants did not necessarily create the original problem, but their presence tells us that the wood had already changed.
The video is a good reminder that trees cannot always be evaluated by appearance alone. A full canopy is encouraging, but it does not guarantee that the trunk or roots are structurally sound.
If you notice carpenter ants, cavities, fungal growth, unusual cracking, or other changes in a tree near your home or outdoor spaces, consider having an arborist take a closer look. A thoughtful assessment can help distinguish a normal feature from a condition that may require monitoring or action.
