Sphecius grandis, also called the western cicada killer, is a colony-forming species of wasp in the genus Sphecius (cicada killer wasps). It shares the same nesting biology as its congener the eastern cicada killer, S. speciosus. S. grandis, like all other species in the genus, mainly provides cicadas for their offspring. It is colonial, mating brooding once a year, in July and early August. Adults are typically 3–5 cm (1.2–2.0 in) long, and amber-yellow with yellow rings on the abdomen.
Members of the genus Sphecius are not habitually aggressive and save their venom for cicadas which they paralyse and take back to their nests. The female catches around four or more cicadas for provisioning, places them in her brood cells and then proceeds to lay eggs in her cells. The species is endemic to Central America and the Western United States, and is found at a higher mean altitude than other species of Sphecius. The males emerge earlier than females, but generally die after only a couple of days.