Across much of the U.S. ant wars are commonly seen taking place on sidewalks and are always a spectacle to behold. This ant is in the genus Tetramorium but confusion on the exact species persisted for many years. It was also introduced from Europe which has a few different species in the genus.

At first it was placed as the species Tetramorium caespitum but that was eventually changed and it was then known as Tetramorium sp. E for a decent period of time. Finally in 2017 a paper was published that shed light on the subject and finally settled the matter. T. caespitum was confirmed as a species but it was still only in Europe. They raised Tetramorium immigrans to species level and assigned this name to the North American specimens and finally ended the long road of confusion.

So now when you see the pavement ant wars while on your walk you can say those are officially Tetramorium immigrans.

Article:

Herbert C. WAGNER, Wolfgang ARTHOFER, Bernhard SEIFERT, Christoph MUSTER, Florian M. STEINER & Birgit C. SCHLICK-STEINER just published “Light at the end of the tunnel: Integrative taxonomy delimits cryptic species in the Tetramorium caespitum complex (Hymenoptera: Formicidae)”. Myrmecological News 25: 95-129 Vienna, October 2017

https://www.researchgate.net/publication/322663055_Light_at_the_end_of_the_tunnel_Integrative_taxonomy_delimits_cryptic_species_in_the_Tetramorium_caespitum_complex_Hymenoptera_Formicidae