Every living specie of plant or animal except the most narrowly localized have been invasive at some point and the territorial expansion or
retreat of species is a unceasing process . The problem is that human transport and ecosystem alteration accelerate this process thousands of times, what take hundreds of thousands or millions of year in natural conditions happened in 50 years . Invasive species are considered by many as a sort of "great devil " in fact an exotic specie become invasive because of special adaptation, superiority or lack of specific predator or parasite in their area of invasion.
We must admit that "super ants " like Solenopsis fire ants or Pheidol megacephala are specially interesting because they represent a summit of ant evolution but we must absolutely refrain from any thing that risk to provoke an invasion not only of "great devil invasive"but also of ants like Attini leaf cutters whom invasion may have cataclysmic consequences in Africa and south Asia.
For areas where the invasive specie is already well established there is no more risk : It have become "native" we like it or not (probably not) so a Solenopsis invicta in an area where they are firmly established is no different from natives ( who were invasive one million years ago).
It is even more the case for Tetramorium caespitum (or T. sp E) who must now be considered the same way as north America natives.
So before becoming hysterical about " great-devil-invasive" we must reflect on the meaning of the word . Better to use one's brain than to be taken to irrational public hysteria and political correctness (pseudo ecological correctness ).