Thanks for the question.

Ants are not known for eating tomatoes but aphids on tomatoes. These aphids are very small so it is possible that you might not have seen them. I don’t think these are carpenter ants as they are usually associated with rotting and decaying wood. For sure if you have an ant nest in your garden, it would not be a nest of carpenter ants. But all these are secondary matters due to your primary concern of keeping ants off of your tomatoes. Take a look at the following as they might give you some ideas:

https://www.gardenguides.com/92119-kill-ants-harming-tomato-plant.html

https://homeguides.sfgate.com/keep-ants-away-tomato-plant-22351.html

https://ourgardenworks.com/ways-to-remove-ants-on-tomato-plants/

https://pestweek.com/ants-on-tomato-plants/

https://www.youtube.com/watch?v=UIyNXQLeYO8

https://www.kellogggarden.com/blog/insect-pest-control/natural-way-to-keep-ants-off-plants/

Good luck and please feel free to get back to us if you have further questions.

Thanks again for your question and I have been giving it some more thought. I enlarged the pictures you sent and I can certainly see “gnawing” marks at the base of the plants. I am thinking that you might be dealing with chipmunks. They dearly love to eat tomatoes. What is occurring at the base is not what I would expect ants to do but is exactly what I would expect chipmunks to do. Chipmunks can be rather elusive and are not easily seen. The mesh on the enclosure around the tomato would certainly enable chipmunks to enter. Now ants may still be going after aphids but it might be chipmunks that are leading to the demise of your plants. See:

https://www.fallsgarden.com/do-chipmunks-eat-tomatoes/ - :~:text=Chipmunks eat tomatoes, among other,spread to other healthy plants.

I would greatly appreciate receiving your thoughts about this possibility. Many thanks.