Sphecius grandis

Distinguishing S. grandis from the other four New World species of Sphecius (S. convallis, S. hogardii, S. speciosus, S. spectabilis) is difficult. The female S. convallis was originally distinguished from the female S. grandis by the yellow marks from the first to third gastral tergites on S. convallis and yellow marks on all tergites for S. grandis. However, this was found to be insufficient for correct identification because the positions of the markings can vary among different wasps of the same species.[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). The 2% percent of S. grandis that overlapped with S. convallis were determined by density of the punctation in colour of the first tergum against the second. The markings on S. grandis males were found to be the same as on females.[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. Experiments found that the wasp has the ability to shift heat from its thorax to its abdomen and that the abdomen is generally kept colder than the thorax. Dead wasps that were placed in the sun reached abnormally high temperatures when compared to those on nearby plants.[12]

After hatching, the offspring feed on the tissue of the cicadas provided by their mother. Males emerge before females and both genders are sexually receptive from emergence in July to early August, when they mate and brood. English naturalist Charles Darwin postulated that the pattern of male emergence before females evolved by natural selection to improve the chances of the male mating. The timing of the emergence of females has evolved to correspond with the similar emergence of the cicada species of the area, Tibicen duryi and T. parallela, which they hunt for the provisioning of their nests.[13] Many have yellow markings located on their tergites (dorsal portion), although some have been found only from the first to fifth tergites.[3]

Sphecius speciosus (eastern cicada killer) shares many behavioral similarities with Sphecius grandis.

Because males emerge earlier than females, the males compete for mating territories surrounding the nests in which the females are located. During a fight, the males risk damaging their wings or appendages by butting and grappling.[14] Another defense technique is to grab another male and carry it high into the air, which is thought to be a demonstration of strength. As a general rule, the larger the male the more predominant he is in battles.[15] Age influences the success in the defense and security of territory; the younger the wasp the greater the chance of a successful takeover of territory. Some small males even engage in non-territorial mating tactics,[16] and delay their emergence so as to have a fairer chance of survival.[17]

On emergence from the nest, the female is sexually receptive but does not choose her mate, but instead copulates with the first male of her species that finds her.[13] Once the female has mated, she rebuffs all advances by other wasps.

Males perch after emerging from their nest. They pick out an area close to a nest with females inside and guard the territory around it so as to have a better chance of mating. They tend to perch on many different substrates such as stumps, pebbles, wood, weeds, grass blades and low tree branches. Males assume an alert posture, ready for a challenge from another male, or from a predator. One study by a behavioral ecologist, John Alcock, showed that a large majority of the marked wasps returned to the same perch day after day, and two males swapped between two different sites.[18] The species rarely perches on the ground.[12]

It shares the same nesting biology as S. speciosus.[7] All cicada killers are ground-nesting insects and nest aggregations can contain up to hundreds of nests, each with a single provisioning female.[4] Their tunnel is mainly made in well-drained, bare sandy soil,[19] frequently under sidewalks,[20] but is generally in full sunlight. Approximately 90% of its life is spent underground as a larva.[21] It rarely infests grounds that are rich in vegetation in order for them to get more sun. Mounds are easily recognizable by their distinctive U-shaped digging entrance.[19]

Sphecius grandis has very similar nesting and feeding habits to other members of its genus, most notably Sphecius speciosus.[7][13] As with S. speciosus,[22] the female hunts for cicadas in low tree trunks, helped by the calls of the cicada males, and paralyses the insect by piercing the central nervous system with her stinger.[19][20] She drags the cicadas back to her nest to place them in brood cells in which she eventually lays one egg per cell.[7] Females carry cicadas that are on average 88% heavier than their own body mass. It has been hypothesised that cicada killers may also have the ability to capture cicadas mid-flight.[10] There are approximately two or more cicadas to each brood cell.[7][19] When the larvae hatch, the cicada provides nutrition for the offspring to feed on.[7]

The wasps preferentially hunt for female cicadas because they have more consumable tissue, but male cicadas are easier to locate, which explains the systemic bias towards male kills.[23] They chiefly hunt for Tibicen duryi, Tibicen dealbata and Tibicen parallela.[24][25] Cicada killers are capable of thermoregulation, which allows them to hunt for cicadas during the day, when the cicadas are most prominent.[11] The species is mostly harmless to humans.[20] Some males when emerging early fly into the trees to feed on sap,[18] and the species has been known to feed on nectar.[19][26]

Stings of this species received a lethality rating of 46 LC measured by LC=μg⁄LD₅₀ (LC="lethal capacity", μg="venom in the insect", LD₅₀="μg⁄g of the venom", g="size of mammal receiving the dose" and LD="lethal dose").[27][28]