The large black wasp you’re seeing in Colorado is most likely the great black wasp, a solitary digger wasp that measures roughly 22 to 28 millimeters long, or just over an inch. Despite its intimidating size, this wasp is not aggressive toward people and plays a genuinely useful role in your yard by hunting grasshoppers and pollinating flowers.
How to Identify the Great Black Wasp
The great black wasp has a deep black body with wings that give off a blue iridescent sheen in sunlight. It has a distinctly pinched, narrow waist, long segmented antennae, large compound eyes, and strong jaws. Fine hairs cover the body, which collect pollen as the wasp visits flowers. Females are a few millimeters larger than males and carry a stinger they use exclusively for paralyzing prey, not for defense the way yellowjackets do.
If the wasp you’re seeing has yellow markings, it’s likely something else. The black and yellow mud dauber is also common in Colorado and shares the same thread-waisted shape, but its body is black with conspicuous yellow stripes on the body and legs. Mud daubers build distinctive mud nests under eaves and overhangs rather than nesting in the ground. Spider wasps, another group of mostly dark-colored wasps in Colorado, tend to be slimmer and hunt spiders specifically rather than grasshoppers.
What They Eat and How They Hunt
Adult great black wasps drink nectar from flowers. They’re surprisingly effective pollinators thanks to those fine body hairs picking up and transferring pollen from bloom to bloom. The hunting, though, is all about feeding the next generation.
Females are active predators of crickets, katydids, and grasshoppers. A female will paralyze her prey with a sting, then carry or drag it back to her underground nest. She places the still-living insect inside a chamber alongside a single egg. When the larva hatches, it feeds on the paralyzed insect over about a week. This sounds grim, but it makes the great black wasp a natural form of pest control. Grasshoppers can be destructive to gardens and crops across Colorado’s Front Range and eastern plains, and every wasp you see is removing several of them from your yard each season.
Ground Nests and What They Look Like
Unlike paper wasps or yellowjackets, the great black wasp is solitary. There’s no colony, no hive, and no swarm of workers defending a shared nest. Each female digs her own burrow about a foot deep into the soil, using her jaws and spiny legs to excavate a series of tunnels. She creates individual chambers, each stocked with one egg and one paralyzed insect.
Once a tunnel is full of developing young, the female seals the chamber entrance. She tamps down the soil using her head and the vibration of her abdomen, and she sometimes uses small tools like pebbles or bits of stick to pack the opening. The nest entrance is a simple, small hole in bare or sparsely vegetated ground. You might notice a few of these holes clustered in the same patch of yard, especially in sandy or well-drained soil. This isn’t a colony; females simply prefer the same type of ground and may nest near each other independently.
Are They Dangerous?
Great black wasps are remarkably docile around people. Males cannot sting at all. Females can sting but almost never do unless physically grabbed or stepped on. They have no colony to defend, which eliminates the aggressive guarding behavior you’d expect from yellowjackets or paper wasps. You can walk past their nest entrances, mow near them, and garden around them without provoking a response.
If you do get stung, the pain is comparable to a typical wasp sting. For most people it causes temporary localized swelling and soreness. Anyone with a known allergy to insect stings should take the same precautions they would with any stinging insect.
Should You Remove Them?
In most cases, great black wasps are worth keeping around. They reduce grasshopper and cricket populations, pollinate your garden, and pose very little sting risk. Their ground nests are temporary. Wasps vacate nests in the fall and don’t reuse the same burrows the next year, so any disruption to your lawn is short-lived.
If a nest is in a high-traffic area where someone could accidentally step into the entrance barefoot, you have a few options. Watering the area heavily can discourage nesting since these wasps prefer dry, well-drained soil. Covering the area with mulch or denser plantings also makes the ground less attractive for future burrows. If you feel removal is necessary, a professional pest control service can handle it safely. Attempting insecticide application on your own requires carefully following product labels and taking precautions to avoid stings.
Leaving the nests alone when possible reduces unnecessary pesticide use in your yard and supports an insect that’s quietly doing beneficial work. After the first hard frosts of fall, the adults die off and the sealed burrows are all that remain underground until the next generation emerges the following summer.