The nesting behavior of species in the Tachysphex terminatus group is presented in phylogenetic order following Pulawski (1988). Eight taxa are treated: T. clarconis, T. antillarum, T. alpestris, T. linsleyi, T. terminatus, T. similis, T. a. apicalis, and T. apicalis fusus. This paper includes a literature review summary for each species, Howard E. Evans' unpublished field notes on T. linsleyi, T. terminatus, and T. similis, unreported insect museum prey records for T. terminatus and T. apicalis fusus, and long-term field studies on T. terminatus, T. similis, T. a. apicalis, and T. apicalis fusus. The field observations were made during the years 1960–2005 and include 929 nests excavated and examined at 52 locations in the central and eastern United States and southern Ontario. Emphasis is placed on: burrow excavation, tumulus leveling, temporary closure, orientation flight, hunting, prey capture, prey transport, nest entry, final closure, burrow design and length, cell depth, cell shape and size, number of cells per nest, cell sequential position, number of prey per cell, prey and wasp weights, total prey biomass per cell, position of prey in cell, and placement of wasp's egg on prey.
