Q: July, 1999 – I have seen dozens of yellow insects hovering over my lawn in a big swarm. Are they yellow jackets?
A: The insects are probably golden digger wasps. These are solitary wasps; they don’t build the hanging paper colonies you’ve feared since childhood. In fact, they are not at all aggressive. You’d have to walk up and smack one before they would give you any notice. They hover over your lawn because they are looking for lawn insects to capture and feed to their offspring. When an insect is captured, the wasp hauls it to a hole she has dug in the ground and lays an egg on her prey. When the egg hatches, a delicious meal awaits the next wasp generation. As you might already have discovered, you can safely walk among them as they hover without much concern on your part. Since they are beneficial, no control is needed.
Other species of digger wasps in the family Scoliidae prey on June beetle larvae. These are typically blue-black in color. They are considered beneficial insects since they prey on lawn grubs. Digger wasp adults are about ½ – ¾ inch long with black antennae and a shiny black head. The front half of the abdomen is black and the back half is brown with two distinct yellow spots (one on each side). The wings are dark blue.
Adult digger wasps can be found feeding on nectar and pollen of flowering plants. You will most likely notice adults flying a few inches to a foot above turfgrass. Part of this flight behavior is a mating dance, in addition to mated female wasps searching for green June beetle grubs in the soil. Amazingly the female wasp locates a grub, digs down into the soil, stings the grub to paralyze it with its venom, and then lays an egg on the grub. The wasp egg hatches and the larva proceeds to consume the grub for the energy needed for the wasp to complete its development. Numerous wasp adults are often are observed flying over turf. Although this may seem intimidating to some, they are not aggressive wasps and are unlikely to sting people, unless handled.
When blue digger wasp activity begins, enjoy watching their behavior and realize they are helping to control the green June beetle grubs in the soil.
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