The ants are 2–3 mm in size, and endemic to the northeastern United States and adjacent Canadian regions.

[1] They do not forage for food, but instead 'scout workers' from the colony seek out nearby host colonies of ants (e.g. Temnothorax longispinosus),[2] steal larvae and bring them back to their own colony.

A small T. americanus colony could consist of a queen, two to five workers and thirty to sixty slaves.

[3] In a study published in Animal Behaviour, researchers showed that T. americanus scouts target stronger colonies over weaker ones to steal larvae from.

[3][4] It was formerly placed as the sole member of the genus Protomognathus.