Large Ground Hornet: Why Are They Burrowing in My Yard?

Eek! What are those giant wasps that burrow underground in my grass and lawn? The first time you see a large ground hornet, or “cicada killer,” you might shriek in fear. The enormous wasps, scientifically known as Sphecius speciosus, can grow more than two inches long, sporting a three-inch wingspan. The body is black or brown, with several prominent yellow stripes and amber wings. It’s hard not to fear the sting of such giant ground hornets, but these fellows are typically aggressive only with the cicadas they feed to their young. Because they have no colony or queen to protect, they have no reason to sting people unless they feel threatened.

For all their ferocious appearance, these huge hornets are beneficial insects that prey on plant-eating cicadas. 

Signs of Giant Ground Hornet Activity

The Cicada Killer While large ground hornets are not dangerous to people, they can cause some lawn damage. The first sign of their presence is often the loose soil they kick up as a female cicada killer burrows in your lawn to build her nest for the eggs and larvae to come. Look for a round opening about the size of a quarter, with a fan of loose soil mounded up to one side of the doorway. Giant ground hornets prefer digging in sandy, open areas or bare soil rather than in a lush, healthy lawn because the soil is far easier to dig.

The other clear sign of large ground hornets is actually seeing one of the huge insects. Giant ground hornets cruise along at low altitudes, looking for cicadas. And since these are solitary wasps, sighting several at a time is unlikely. Cicada killers can also be recognized by their distinctive low, slow flight pattern, which is different from the intricate flights of bees and other wasps.

Impact on Lawns

There’s no denying that giant ground hornets can do some damage to your lawn. The loose soil kicked up around their burrows is unsightly. And it can be scary to hear a loud buzzing, look up, and see the enormous wasp. But these fearsome-looking insects have no interest in bothering you, and the males have no stinger to use even if they wanted to. Cicada killers’ burrows even aerate the soil, offering a small benefit in exchange for the nest.

Lifecycle and Behavior

It might surprise you to learn that adult large ground hornets are vegetarians, despite the name “cicada killers.” They feed on flower nectar. It is the larvae that consume cicadas.

Mating and Nesting

In summer, typically June and July, adult cicada killers emerge from the burrows where they overwintered as larvae. Soon after emerging, the giant ground hornets mate, with the males competing over prime nesting sites. They look for sandy soil in full sun, with sparse plants where soil is easy to dig. After mating, the males die, and the females construct their nests, burrowing into the soil to form a labyrinth of tunnels and individual cells.

Hunting and Provisioning

Once her nest is ready, the female ground hornets hunt for cicadas, flying low and slow as they search. When they find one, they sting the cicada to paralyze it. The female then carries her much larger prey back to the nest, installing it in one of the cells she has prepared. There, she lays an egg on the cicada, which serves as live food for her soon-to-hatch larva. Next,she seals up the burrow. Once she finishes laying her eggs, she dies.

Larval Development and Pupation

The eggs hatch in a few days, and hungry larvae emerge to feast on the living cicada. The larva continues feeding, molting several times as it consumes the insect, earning the name “cicada killer.” Once the larva has reached a sufficient size, it spins a cocoon for pupation. It overwinters in its cocoon, emerging in the summer and digging its way out of the burrow to seek a mate.

Prevention and Management Strategies

Large ground hornets are beneficial, no threat to people, and should be left alone whenever possible. But you don’t have to resign yourself to burrows in your lawn. Your primary defense is a lush, healthy lawn. All of our lawn care services help to prevent ground wasps by improving the overall health of your grass.

Grass roots are tough to dig through, so cicada killers look for bare or sparse patches for their nests. Appropriate lawn fertilization and overseeding are particularly effective at keeping the hornets out of your lawn. So, too, is generous watering. Wet soil can cause their tunnels and cells to collapse, possibly one of the main reasons the insects prefer dry soil. Just remember to water in the morning rather than late afternoon or evening. You don’t want the grass to remain wet overnight.

If you’re facing a major infestation or your attempts to evict the giant ground hornets have been unsuccessful, contact Lawn Pride®. In addition to enhancing the health and beauty of your lawn, our perimeter pest control service can take cicada killers out of your way.

Safety Considerations

The large hornets that burrow in the ground are active top-side just for the summer months. It’s best to leave them alone. They pose no threat to people unless they are harassed. Then, the sting packs a powerful punch. Curious children and pets may be stung if they catch a female cicada killer (males have no stinger). If you see a burrow on your property, keep pets and little ones away from it. If you’re working in the garden near a burrow, wear long pants and a long-sleeved shirt, just in case. When mowing the lawn, avoid disturbing the burrow so you don’t provoke the hornets.

Whether you need help getting rid of large ground hornets or just want to enjoy the loveliest lawn in the neighborhood, Lawn Pride is here to help. We know you’ll be pleased with our services because the Neighborly Done Right PromiseTM backs everything we do. Request a free estimate today!