The Hobo Spider isn't considered a particularly venomous species, but there are some scientists that say it can become very aggressive if someone was to get near it's eggs. The CDC may not consider it a dangerous spider, but I'd still want to stay away. It can be found throughout the entire state.
Need to identify a brown recluse spider? Well we do know that recluse spiders have three pairs of eyes, so you may have to look a lot closer than you actually want to. They also usually have a violin pattern on their bodies, and are very active at night. If you are bitten by a recluse spider, and develop a blue patch around the bite, make sure you get this checked ASAP! This can occur within 72 hours after receiving the bite.
Yellow Sac Spiders have an albino color to them and can be found mainly in homes throughout Colorado, especially during the winter. They are definitely aggressive and can bite several times if they feel like they are threatened. They especially love to hide in piles of clothes, so keep that in mind if you haven't done laundry in a while!
In my opinion, the black widow spider is the scariest looking spider in not only Colorado but the entire country. However, one thing I learned about them is that they rarely bite you when they aren't in their web. When in a web, that means the female is most likely trying to protect her unborn, which will make her get nasty on you. Bites from a black widow can be very dangerous, so if you start to see swelling after a bite, get medical attention immediately.
Their habitat is expanding in Colorado. However, as of this writing, tarantulas still haven't made their way to Northern Colorado yet. Are tarantulas dangerous like the rest of the spiders on this list? No. But they can bite if they are being handled too rough. While they may not carry venom, the body hairs on a tarantula can definitely be uncomfortable and they can sting.