The large black wasp you’re seeing in Michigan is almost certainly the great black wasp (Sphex pensylvanicus), a solitary digger wasp found throughout the eastern United States. These insects are striking, often over an inch long, entirely jet black with dark, iridescent blue-black wings. Despite their intimidating size, they are one of the least aggressive wasps you’ll encounter.
How to Identify a Great Black Wasp
Great black wasps are hard to mistake for anything else. They’re large, typically 1 to 1.4 inches long, with a completely black body and a noticeable narrow “waist” between the thorax and abdomen. Their wings have a dark, smoky blue or violet sheen that catches the light. Unlike yellowjackets or paper wasps, they have no yellow, white, or red markings whatsoever.
A few other black wasps show up in Michigan that could cause confusion. Black mud daubers are slimmer with an extremely long, thread-like waist and build tubular mud nests on walls and eaves. Spider wasps (Pompilidae) are also dark-bodied but tend to be smaller and have noticeably long, spindly legs. If what you’re seeing is large, all black, and hovering low over bare soil or a lawn, it’s most likely a great black wasp.
Where and When They’re Active
Great black wasps are warm-season insects. In Michigan, adults typically appear in late June or July and remain active through August and into early September. You’ll most often spot them in two places: visiting flowers (they feed on nectar) or flying low over sandy, bare, or compacted soil where females dig their nests.
They favor open, sunny ground with sparse vegetation. Garden edges, gravel paths, patchy lawns, and sandy flower beds are common nesting spots. If you’ve noticed small, pencil-sized holes in bare soil with a black wasp coming and going, that’s a nesting female.
How They Nest and Reproduce
Unlike yellowjackets or hornets, the great black wasp is solitary. There’s no colony, no queen-and-worker hierarchy, and no shared hive to defend. Each female digs her own burrow, working about a foot down into the soil and creating a series of branching tunnels and chambers using her jaws and spiny legs.
Each chamber gets a single egg and a paralyzed insect, usually a katydid, grasshopper, or cricket. The female stings her prey to paralyze it (not kill it), then carries or drags it underground as a fresh food supply for the developing larva. Once a tunnel is stocked and sealed, she moves on to dig another. She even uses small tools, tamping down soil over the entrance with pebbles or bits of stick and vibrating her abdomen to compact the surface.
The larvae develop underground through fall and winter, pupating in the spring and emerging as adults the following summer. Each female may provision several burrows in her short adult life of a few weeks.
Are They Dangerous?
Great black wasps are remarkably docile toward people. Because they’re solitary, they have no colony to defend, which removes the trigger for the aggressive swarming behavior you’d get from yellowjackets or bald-faced hornets. A female focused on digging or hunting will generally ignore you entirely, even if you’re standing just a few feet away.
They can sting if physically grabbed or stepped on, and females do have a functional stinger (males cannot sting at all). The sting is comparable to a typical wasp sting: a sharp, brief pain with localized swelling that resolves within a day or two for most people. But unprovoked stings are extremely rare. You’d essentially have to trap one against your skin to get stung.
Why They’re Worth Keeping Around
Great black wasps pull double duty in your yard. As predators, they help control grasshopper and katydid populations, insects that can damage gardens and crops. As adults, they feed heavily on flower nectar and are effective pollinators, visiting plants like milkweed, sweet clover, and various wildflowers throughout the summer.
Because they nest in the ground individually rather than building large communal nests, they also don’t cause structural damage to buildings, decks, or eaves the way paper wasps or carpenter bees might.
What to Do About Ground Nests
In most cases, the best approach is to leave them alone. A solitary wasp nesting in a garden border or unused patch of yard poses virtually no risk. The burrows are small, temporary, and won’t damage your lawn. The wasps will be gone by early fall.
If nests are in a high-traffic area, like along a walkway where kids play barefoot, you can discourage nesting by changing the soil conditions. Great black wasps prefer dry, bare, compacted ground. Keeping the area well-watered, adding mulch, or encouraging thick grass cover makes the spot less attractive for next season. You can also simply mark the area and avoid it for the few weeks the wasps are active.
Insecticide treatment is rarely warranted for solitary wasps. If you do feel the need to address a nest, a dust-based insecticide applied at the burrow entrance at night (when the wasp is inside and less active) is the standard approach. But given how non-aggressive these wasps are and how much ecological good they do, most entomologists recommend coexistence over control.