Hello Wendy,

More information would be helpful in order for us to suggest a course of action, though the ants may simply relocate if the nest is too badly damaged or disturbed.

Carpenter ants do not kill trees - they establish nests in wood that is already compromised by moisture and fungi. While wood at the heart of tree trunks is naturally dead already, its decay suggests it was exposed to the elements by way of broken limbs, lightning damage (removing bark), or other wounds. Ants may also be seen on the tree's bark if they are using scale (a type of pest insect) as a source of food; the scale would be feeding on tree sap. Treating the tree for ants alone is not recommended, though if the tree is in good condition but has a notable scale population, then using bait to kill the colony (so the scale can be dealt with by natural predators) might be useful.
https://extension.umd.edu/resource/carpenter-ants

What is the overall condition of the tree? Can you share photos of its appearance and any particular symptoms you find concerning? Was it being trimmed to selectively remove dead wood or problematic branches?

Miri

Miri,

I can take some photos and send them along. The trimming was of dead branches. To me, but I’m not a tree expert, the tree seems healthy; however, as you said, the presence of carpenter ants indicates otherwise.

Best,

Wendy

Miri,

Attached please find three photos. One shows red ants, one shows black ants (carpenter ants?), and one shows the tree (it’s the one in the center of photo). Please let me know if you need additional photos.

Thank you,

Wendy

Miri,

Here are a few more photos.

Thanks again,

Wendy

Thank you for the photos. Based on the tree's overall appearance, it definitely does not look like it needs removal, at least not for reasons tied to any ant presence. Even so, consulting with a certified arborist about any concerns is sensible since they can inspect for issues that might not translate well in photographs. (Some tree services are overseen or performed by arborists while others are not.)

They mentioned an "infestation" of the black ants (which do look like carpenter ants), but it doesn't sound like they distinguished between ants coming and going from a nest or rather a number of them roaming around on the bark. Aside from "farming" scale, ants do prey on a number of other insects and might simply be foraging in the canopy rather than causing any problems for the tree itself. The red ants are another species and are probably unrelated (in terms of their activities) to the black species.

If the tree still needs dead wood removed for the safety of people or property, perhaps the tree service can come back to finish the pruning in winter, when any ants would be relatively inactive. A tree this size should not need pest control company treatment; even if a high population of scale insects were present, they usually don't cause much damage, and any insecticide used to try to control them risks harming beneficial insects and impacting the tree's value to wildlife (like foraging birds, especially since this is an oak).

Miri

You're welcome.

Routine arborist assessment isn't needed for trees that appear healthy, though aside from any incurred expense it won't hurt to do so periodically; we don't have any particular time interval to recommend. Rather, when symptoms of stress or an ailment manifest, or when pruning for tree health or aesthetics is considered, those are times their consultation is definitely prudent.

Miri

Miri,

Okay. Thank you. One more bit of information a board member, who interacted with the tree service employee, said she was told the employee stopped pruning because he thought the tree was too weak to withstand any more. I apologize I didn’t know this information earlier. Does that information change what needs to be done with the tree? Or are we okay to wait until winter to continue pruning?

Best,

Wendy

The tree doesn't look too bad in the photos, so we aren't certain what the tree service was referring to by saying "weak." Dead wood can always be removed, so if that's what they were pruning, this has no impact on the health of a tree. (It's a positive, actually, since it avoids this wood damaging healthy branches if it comes crashing down in a storm.) According to a pruning calendar published by Virginia Tech, the best time to trim oaks (regarding live wood) is between September and February, with the ideal window being November-December.

Miri

You're welcome.