If, in late summer, you notice a cloud of wasps careening in arcs and figure eights across the surface of the grass, don’t be alarmed and don’t reach for the pesticides. Celebrate these native beneficials that consume grub larvae and pollinate flowers! They are scoliid wasps– likely Scolia dubia or a close relative.
Although scoliid wasps may look intimidating when they congregate, they will only sting humans if severely harassed. Green June beetle and Japanese beetle grubs, on the other hand, have plenty to fear. A scoliid wasp stings a grub to paralyze it, lays an egg on its surface, and provisions an underground cell with additional paralyzed grubs for its larva to eat as it matures. She then repeats this process, dooming additional grubs as live feed for her offspring in other chambers.
Your best chance to examine these attractive wasps is while they feed on nectar. They enjoy a wide variety of flowers, including white clover and mountain mint. They have lovely metallic blue wings and a pattern of yellow spots on the abdomen that varies with the species and gender. Their distinctively curved back is the origin of their scientific name– think “scoliosis.”
Scoliid wasps’ many common names, including flower wasps, scarab hunters, and scarab hawks, remind us of their multiple functions in our ecosystem and their extraordinary value for gardeners.