Wasps in the genus Sphecius are not habitually aggressive and use their venom mainly to paralyse cicadas which they take back to their nests to feed their young.

S. grandis is endemic to Central America, Mexico and the Western United States, and is found at a higher mean altitude than other species of Sphecius.

The western cicada killer males emerge earlier than females, but generally die after only a couple of days.

Sphecius grandis can be distinguished from S. convallis (the Pacific cicada killer wasp) by the coloration pattern of the gastral tergites.

The western cicada killer was first described by American naturalist Thomas Say in 1824 in Madera Canyon, Arizona, as Stizus grandis.

Analysis of mitochondrial DNA showed that the western cicada killer contains two divergent clades, which may represent distinct species.

[4] Ranging in size from 3 to 5 cm (1 to 2 in) in length, the western cicada killer is very similar to its eastern cousin, Sphecius speciosus, with a rufous black hue to the body, amber stripes and a yellow abdomen.

[3][5][6] The western cicada killer has rufous spots on its first to second tergites and yellow markings can generally be found from first to fifth, although there is some variation.

[6] In Steven J. Phillips' book A Natural History of the Sonoran Desert, he referred to them as superficially resembling "huge yellowjackets or hornets" and stated that they are "powerful fliers with compound eyes".

[3] Charles W. Holliday and Joseph R. Coelho devised a new key in 2004 to identify the Sphecius species, examining 4,451 wasps among the five New World species, and noting that 98% of the female S. convallis wasps examined had yellow markings on gastral tergites one to four (or fewer) and S. grandis had 98% yellow markings from tergites one to five (or more).

[3] It has been found that the western cicada killer wasp is capable of thermoregulation which enables them to maintain territories during the day.

[11] A study by Joseph R. Coelho showed that during territorial patrolling the species had a high and regulated thorax temperature.

They tend to perch on many different substrates such as stumps, pebbles, wood, weeds, grass blades and low tree branches.

[4] Their tunnel is mainly made in well-drained, bare sandy soil,[19] frequently under sidewalks,[20] but is generally in full sunlight.

A study showed that the mean elevation for S. grandis was 755 m ± 23.3 m, compared with the lower results of S. speciosus (219 m ± 4.7 m), S. convallis (582 m ± 30.9 m) and S. hogardii (18 m ± 5 m).

[29] Sphecius grandis wasps frequently interact with humans because of their tendency to make their nests in backyards, gardens and sidewalks.

[20] Pest control is mostly unneeded as they nest in areas with little to no vegetation, usually ignore people, and females are not aggressive, tending to save their venom for their cicada prey,[6] but will sting if they are grabbed or stepped on.