The large colorful hunting wasps, Scolia dubia (Order: Hymenoptera; Family Scoliidae), may look intimidating, but are harmless to you unless you grab one and force it to sting in self defense. Adults are most numerous late in summer (usually August) and are present now on flowers (see August 17 post for example) and hovering over lawns in search of food for their young. Their larval food is actually grubs, primarily Green June beetle larvae, that feed on and damage grass roots in lawns.
The adult grub-wasps dig into the soil when they “smell” (anyone who has seen holes made by skunks digging for grubs in their lawn knows this is possible) a grub, sting it to paralyze it, then lay an egg on it. The paralyzed grub is then helpless to defend against the hatched grub-wasp larva that will consume this fresh food supply until it is fully grown. The grub-wasp larva then pupates in the soil, ready to emerge as an adult the following summer. If there are enough of these wasps in your yard, they can help reduce the numbers of grubs in your lawn, providing natural control of pests. Here's a video of a grub-wasp feeding on nectar: