The behavioral and ecological activities of Tachysphex tarsatus (Say, 1823), T. miwok Pulawski, 1988, T. musciventris Pulawski, 1982, and T. clarconis Viereck, 1906 were studied in spring 2010–2014 at Montana de Oro State Park and El Moro Elfin Forest, San Luis Obispo County, California. Adult wasps were active from late February (T. miwok)-March (T. miwok, T. clarconis, T. tarsatus) to April-early May (T. miwok)-late June (T. clarconis, T. tarsatus) in association with ample seasonal rainfall, moist malleable sand, reduced coastal fog, increased sunshine, flush of low growth flowering plants, and abundance of nymphal prey Caelifera (Orthoptera). The absence of these species in summer 2009–2014 was probably related to extremely limited rainfall, dry loose sand, frequent coastal fog, senescence of flowering plants, and substantially reduced number of nymphal prey Caelifera. Tachyphex amplus was active from July to September 2011–2012 under droughty summer climatic conditions. The five species have adapted to a treeless environment, moderately windy (13–24 mph) maritime climate, periodic fog, cool spring temperatures, and rainfall-deprived summers. Tachysphex miwok was univoltine and provisioned nests with early instar nymphal Conozoa texana (Bruner, 1889) and Oedaleonotus phryneicus Hebard, 1919 (Acrididae). Tachysphex tarsatus was uni- or bivoltine and stocked late instar nymphs and adults of the same acridid species in its nests. Tachysphex clarconis was also uni- or bivoltine but polyphagous, provisioning its nests with two families (Eumastacidae, Acrididae) and six genera of Caelifera. Eumastacidae (Morsea californica Scudder, 1898) is reported as a new host family for the genus Tachysphex in North America.