Colorado is full of outdoor adventures, but some creatures lurking nearby pack a venomous punch. Knowing which ones to watch out for can keep your hikes and yard work safe.
I’ve spotted a few myself, and they’re definitely worth respecting from a distance. Here’s what every Colorado resident should know about these dangerous visitors!
1. Western Diamondback Rattlesnake
These iconic pit vipers possess heat-sensing organs that help them locate prey with remarkable precision. Their distinctive rattle serves as a warning when they feel threatened.
Throughout Colorado’s western regions, diamondbacks prefer rocky areas and shrublands. Their venom contains powerful hemotoxins that can cause tissue damage and serious complications if not treated promptly.
2. Prairie Rattlesnake
Most commonly encountered in Colorado’s eastern plains and foothills, these rattlers cause the majority of snakebites in the state. They’re typically tan or light brown with dark oval blotches along their backs.
When hiking in Colorado’s grasslands, watch your step and listen for their warning rattle. Prairie rattlesnakes are generally not aggressive but will strike if they feel cornered or surprised.
3. Massasauga Rattlesnake
Smaller than their rattlesnake cousins, Massasaugas reach only about 2-3 feet in length. Their habitat in southeastern Colorado includes grasslands and semi-desert shrublands where they hunt small mammals and lizards.
Colorado wildlife officials consider them a species of special concern due to habitat loss. While their venom is less potent than other rattlesnakes, medical attention is still essential following any bite.
4. Black Widow Spider
Recognizable by the red hourglass marking on their abdomen, these notorious arachnids lurk in dark, undisturbed areas. Around Colorado homes, they’re commonly found in woodpiles, garden sheds, and under rocks.
Only female black widows pose a significant threat to humans. Their neurotoxic venom can cause painful muscle cramps, nausea, and in rare cases, more serious symptoms requiring immediate medical care in Colorado hospitals.
5. Brown Recluse Spider
Despite common beliefs, true brown recluse spiders are extremely rare in Colorado. They’re identified by the violin-shaped marking on their back and their six eyes arranged in pairs.
Colorado residents often misidentify harmless spiders as brown recluses. The actual range of these venomous arachnids barely touches the state’s southeastern corner, making encounters unlikely but still worth knowing about.
6. Western Yellowjacket
Aggressive defenders of their territory, these social wasps build paper nests in Colorado’s ground cavities and structures. Unlike honeybees, yellowjackets can sting repeatedly without losing their stinger.
Late summer picnics in Colorado parks often attract these yellow-and-black insects to sweet foods and drinks. For most people, stings cause temporary pain, but those with allergies may experience severe reactions requiring emergency treatment.
7. Tarantula Hawk Wasp
Sporting a metallic blue-black body with rusty orange wings, these enormous wasps hunt tarantulas as hosts for their young. Their sting ranks among the most painful insect stings in the world.
During late summer in southern Colorado, males gather in hilltop mating displays. Despite their intimidating appearance and painful sting, they rarely bother humans unless handled or stepped on barefoot.
8. Striped Bark Scorpion
Found primarily in Colorado’s southwestern desert regions, these light brown scorpions have two dark stripes running down their backs. They glow bright blue-green under ultraviolet light, making them easier to spot at night.
While hunting for shelter, they occasionally wander into Colorado homes. Their sting causes intense pain but is rarely dangerous except to small children, elderly individuals, or those with allergies.
9. Honeybee
Essential pollinators for Colorado’s agriculture and wild plants, honeybees only sting as a last resort. Once they sting, their barbed stinger remains in the skin, causing the bee’s death.
Colorado beekeepers maintain thousands of hives throughout the state. For most people, stings cause temporary discomfort, but approximately 2% of the population experiences severe allergic reactions that can be life-threatening without immediate treatment.
10. Midges (No-See-Ums)
Nearly invisible to the naked eye, these tiny biting flies pack a surprisingly painful punch. Around Colorado’s lakes and streams, they emerge in swarms during dawn and dusk hours.
Female midges use specialized mouthparts to slice skin and feed on blood. While not technically venomous, Colorado outdoor enthusiasts often mistake their itchy, painful bites for more dangerous creatures due to the disproportionate discomfort they cause.
11. Blister Beetles
Rather than stinging or biting, these beetles release a caustic substance called cantharidin when crushed or handled. This chemical causes painful skin blisters within hours of contact.
Colorado gardeners sometimes encounter these insects on vegetables and flowering plants. While not aggressive, accidentally brushing against them while working outdoors can result in uncomfortable skin reactions that may take weeks to fully heal.