The large, hairy spiders found in Colorado are generally dark brown to black. You are more likely to come across these spiders in the southeast part of the state this time of year as mature males migrate in late summer and early fall. They pose little hazard to people, but their bite can be painful. However, the venom released does not cause any serious complications in humans.
Considered harmless to humans, the hobo spider is found in many parts of Colorado.
According to the Colorado State University Extentsion Office, black widow spiders rarely, if ever, bite when not within a web. Bites may be more likely if the female is tending an egg sac in the web, which she will defend. They produce a toxin that affects the nervous system. Muscle and chest pain or tightness are some of the most common reactions to the widow toxin.
Although very rare in Colorado, the brown recluse spider has been identified in the state at times. According to the Colorado State University Extension Office, the brown recluse are, by far, the most commonly misidentified spiders in Colorado.
Sac spiders are active hunters. They get their name because they spend daylight hours in a flattened silken sac, typically located in the upper corners of rooms or in wall cracks. The bite, although painful, usually causes no other symptoms and the pain subsides after a few minutes.
A deceiving and beautiful creature can be found in much of the United States, including in Colorado. A species of wasp that goes by the name of dasymutilla occidentalis, better known as the "Cow Killer" or "Red Velvet Ant" is currently at its peak of activity. Although the sting is dangerous, they won't actively seek out humans, so admiring the wasps at a healthy distance is recommended.
The northern scorpion (Paruroctonus boreus) occurs throughout the counties along the Utah border and is a species with the most northerly distribution of any scorpion, reaching into southern Alberta, according to Colorado State University. No species of scorpions that occur in Colorado have venom associated with dangerous complications.
The northern desert (black) hairy scorpion is also present on the West Slope, but in more limited areas such as Dinosaur National Monument, according to Colorado State University. No species of scorpions that occur in Colorado have venom associated with dangerous complications.
The common striped bark scorpion (Centruroides vittatus) is widespread in southeastern Colorado, with 1-70 about its most northern range, according to Colorado State University. No species of scorpions that occur in Colorado have venom associated with dangerous complications.
Of the 25 species of snakes in Colorado, the western rattlesnake (Crotalus viridis) and the massasauga (Sistrurus catenatus) are the only venomous species. The western rattlesnake appears in most habitats throughout the state. The massasauga, however, is limited to the southeastern grasslands. Even with a high survival rate, rattlesnake venom can lead to significant pain and suffering in its victims, according to Colorado State University.