Colorado has no true hornets in the strict scientific sense, but it does have one insect that carries the name: the bald-faced hornet. This black-and-white wasp is the closest thing to a hornet you’ll encounter in the state. The northern giant hornet (sometimes called the “murder hornet”) has never been found in Colorado or any state outside Washington. Most large, intimidating wasps spotted by Colorado residents turn out to be bald-faced hornets, cicada killers, pigeon horntails, or tarantula hawk wasps.
The Bald-Faced Hornet
The bald-faced hornet is the species most Coloradans are thinking of when they search for hornets. It’s technically a yellowjacket (genus Dolichovespula), but its common name has stuck for generations. Adults are distinctly marked in black and white, with an elongated body that ends in a blunt point. Workers typically measure 10 to 14 mm, while queens and larger individuals exceed 15 mm. Unlike bees, they’re only sparsely hairy.
These hornets build large, enclosed paper nests in shrubs and trees, never in the ground. A single overwintered queen starts a new nest each spring using chewed plant fibers like weathered wood. The finished product has a papery envelope with a scalloped texture covering multiple tiers of horizontal combs inside. Coloration of the envelope can vary quite a bit. Nests are used for one season only and abandoned once cold weather arrives.
Other Stinging Insects You’ll See
Colorado is home to several yellowjacket species, multiple paper wasps, and a handful of solitary wasps that people regularly mistake for hornets. Knowing which one you’re dealing with matters because their behavior, nesting habits, and sting risk differ significantly.
Western Yellowjacket
The western yellowjacket is the number one cause of stings in Colorado. It’s stout-bodied with bold yellow and black markings and builds paper nests enclosed by a paper envelope, usually underground. Unlike bald-faced hornets, western yellowjackets scavenge dead insects, earthworms, carrion, and garbage, which is why they show up uninvited at picnics and trash cans.
European Paper Wasp
This species has spread through many urban areas in Colorado over the past several years. It has a slimmer body than a yellowjacket and builds small, open-celled paper nests above ground in places like playground equipment, open-ended poles, soffit vents, and other man-made structures. European paper wasps are generally docile and feed on live insects, making them effective natural pest controllers for garden pests like cabbageworms and tomato hornworms. Stings happen mostly when people accidentally disturb a nest in an unexpected spot. They’re less common in rural parts of the state.
Cicada Killers and Tarantula Hawks
Both of these are large solitary wasps that look alarming but pose little threat to people. The cicada killer can reach nearly two inches long and digs burrows in sandy soil. Tarantula hawks are metallic blue-black with orange wings. Neither is aggressive toward humans, though a tarantula hawk sting is famously painful if you’re unlucky enough to provoke one.
No Murder Hornets in Colorado
The Colorado Department of Agriculture has addressed this directly: northern giant hornets have not been positively identified in Colorado or any state besides Washington. Many people who report suspected sightings are seeing one of the species listed above. If you spot a large wasp in Colorado, it is almost certainly native or at least long-established, not an invasive giant hornet.
Seasonal Activity and Colony Lifecycle
Hornet and wasp activity in Colorado follows a predictable annual cycle. In spring, a single queen emerges from her winter shelter and begins building a nest alone, laying eggs and raising the first generation of workers by herself. Through June and July the colony grows rapidly, with workers taking over foraging, nest defense, and feeding larvae.
Populations peak in late August, and this is when stings are most likely. Colonies are at maximum size, food demands are high, and workers are actively defending territory. Activity remains noticeable through September, then gradually declines through October as the colony shifts its priorities. The queen begins producing reproductive males and new queens instead of workers. Once those new queens leave to mate, the original colony starts to collapse.
After consistent hard freezes, worker wasps die from cold exposure. Males die shortly after mating. The original queen dies. Only newly fertilized queens survive, tucking themselves into sheltered spots to wait out winter and start the cycle again the following spring.
What To Do About a Nest
If a nest isn’t in a high-traffic area, the simplest approach is to leave it alone until the colony dies off naturally at the end of the season. Once abandoned, you can safely remove the empty nest. Colorado State University Extension recommends washing the area with a strong jet of water afterward to eliminate lingering scent markers that might attract future nest-building.
For nests in spots where people or pets are at risk, insecticides labeled for wasps and hornets can destroy individual nests. Apply them in the evening, when most of the colony has returned for the night. Bald-faced hornet nests high in trees are best handled by a professional, since these insects defend their nests aggressively and can sting repeatedly.
Sting Risks and Allergic Reactions
A normal sting produces pain, redness, and localized swelling that resolves within a few hours to a couple of days. A large local reaction causes swelling that spreads well beyond the sting site. A sting on your forearm, for example, might cause your entire arm to swell. This is uncomfortable but not life-threatening on its own.
Anaphylaxis is the serious concern. Between 1.6% and 5.1% of people in the U.S. have experienced a life-threatening allergic reaction to insect stings at some point. Symptoms include flushing, hives, difficulty breathing, and a drop in blood pressure. These reactions can progress very rapidly. Anyone who has had a systemic reaction to a sting in the past should carry injectable epinephrine. Roughly 72 people die from insect stings in the U.S. each year, so while severe reactions are uncommon, they’re not negligible for people with known allergies.