[5] The black and orange colour pattern, combined with the wasps' jerky behaviour and strong odour, give an aposematic warning to predators.

[6] Younger females of P. grossa have long, coarse hairs beneath the femur of the front leg, but these can be worn off in older specimens.

[5] The female wasps hunt in a crepuscular pattern, avoiding the intense daytime sun, by flying low over the ground, detecting their prey using vision or scent, possibly detecting the occupied burrows by the scent of the silk curtain the spider weaves over the entrance.

[7] In Big Bend Ranch State Park, Texas, four species of plants accounted for 73.6% of all plants which were used by adults for feeding; these were the milkweeds: Asclepias texana and Asclepias sperryi; Mexican buckeye Ungnadia speciosa, and honey mesquite Prosopis glandulosa.

[9] Wasps of the genus Pepsis do seem to be important pollinators of milkweeds which are regarded as noxious weeds, as they are poisonous to grazing livestock.

[10] P. grossa forms mixed-species, mixed-sex aggregations that appear to be defensive in nature and probably assist in the location of resources and mating opportunities.

[12] Wasps of the genera Pepsis and Hemipepsis produce large quantities of venom, and when stung, humans experience immediate, intense, excruciating short-term pain.

The pain experienced by the potential predator also forms an enabling basis for the evolution of aposematic coloration, aposematic odor, and a Müllerian mimicry complex involving most species of tarantula hawks as well as Batesian mimicry with other harmless insect species.

[13] Other Batesian mimics include the fly Mydas xanthopterus[14] as well as other Diptera, Coleoptera, moths, acridid grasshoppers, and other Hymenoptera.