Does anyone know what insect causes this kind of damage?
Hello @Else
The small, evenly scattered holes visible in the bark are most likely caused by wood-boring insects, particularly beetles that tunnel into the outer layers of the tree. A common source of this type of damage is the Ambrosia beetle or other similar bark-boring beetles. These insects drill into the bark and outer wood to create small galleries where they live and reproduce. When the adult beetles eventually emerge, they leave behind the small, round exit holes that become visible across the trunk. This is why the holes often appear scattered over a wide area of the bark rather than being concentrated in one location.
The pattern of damage in the photo fits well with beetle activity. The holes are very small and circular, which is typical of beetle exit holes, and they appear randomly distributed rather than arranged in rows or lines. Birds such as cockatoos or other wildlife that peck at trees generally leave much larger and more irregular damage, so the fine, pin-sized holes seen here strongly suggest insect boring rather than animal activity. The slight darkening and weathered texture around some of the holes is also consistent with older insect tunnels that have been exposed as the bark ages and expands.
Unfortunately, infestations like this are difficult to treat once they have occurred because the insects spend most of their life cycle inside the tree rather than on the surface. Wood-boring beetles typically lay their eggs beneath the bark, and the larvae develop within the tunnels they create in the wood. Because they are physically protected inside the tree, surface sprays or treatments generally cannot reach them. By the time the holes become visible, the insects responsible have often already completed their development and exited the tree. This means chemical treatments are rarely effective and can sometimes do more harm than good if applied unnecessarily.
For this reason, management usually focuses on improving the overall health and resilience of the tree rather than attempting to eliminate the insects directly. Many of these beetles are opportunistic and tend to target trees that are already stressed by drought, soil compaction, root disturbance, or other environmental pressures. Healthy, vigorous trees are often able to tolerate minor boring activity without significant long-term damage. Maintaining consistent watering during dry periods, ensuring the soil around the roots is not compacted, and applying a suitable mulch layer around the base can all help support the tree’s natural defences. Keeping mulch a short distance away from the trunk is also important to prevent excess moisture from sitting against the bark.
In most cases, a mature tree with scattered exit holes like these can continue to grow normally if its general health is maintained. Monitoring the tree over time is helpful, particularly to see whether new holes continue to appear or whether branches higher in the canopy begin to decline. If the activity appears to increase significantly or the tree shows signs of stress such as dieback, it may be worth having the tree assessed by a local arborist who can evaluate its overall condition and determine whether further action is needed.
If you need further assistance, please let us know.
Eric
