FAQ - Answer
You are right in that the two are coincidental and not related. Most likely the ants are attracted to the trees because of the presence of Homopterid insects (aphids, whiteflies, scale). The ants will tend these insects for the sugary honeydew that they produce and use it as a food source. The hollow trunks are most likely the result of fungi/bacteria, fire and time. In some cases past fire events can create an injury that over time will result in a hollowing of the interior heart wood from secondary pathogens. Likewise, fungi/bacteria can enter into the tree from a host of causes, wind damage, insects, etc. Most likely the trees with the hollows are quite old, regardless of size, and have been exposed to a number of pathogens that have impacted the wood.