Common Colorado House Spiders
House spiders in Colorado are rather common depending on the season and local climate. While these spiders may seem somewhat intimidating, particularly for children, most of the more common spiders found in Colorado are harmless; however, it's important that homeowners understand which of these spiders are harmless, and which should be avoided.
Funnel Weaver Spider
Funnel Weaver Spiders are one of the more common types of spiders you'll see in Colorado homes. People can generally find these spiders in late summer and early fall, though they pose no threat to humans. Homeowners can generally find these spiders indoors and in recessed areas, but they can also be found outdoors in shrubs or thicker grass areas. The Funnel Weaver does not hunt by leaving its web; the Funnel Weaver builds a funnel-type web that's meant to trap any prey that enters into it.
Colorado State University notes that residents often mistake the dark-brown Funnel Weaver for the poisonous Brown Recluse, with the Funnel Weaver lacking the distinctive marks such as a "violin" shape marking and its three sets of eyes. The Funnel Weaver has four sets of eyes.
The Sac Spider, referred to by its scientific genus name Cheiracanthium, is a very common spider in fall months. Sac Spiders are active hunters, and typically leave their silk sacs at night to hunt for prey. According to Colorado State University, the Sac Spider is most responsible for spider bites among humans, especially at night and in homes. However, the University does not include the Sac Spider among the potentially dangerous spider species. The Sac Spider is more likely to be a nuisance than a threat.
The Sac Spider can be easily identified by its pale color.
Black Widow Spider
The Widow is a commonly-seen type of spider in Colorado. This spider is potentially dangerous to humans due to its nerve toxin. These spiders often seek out areas that are normally undisturbed and dark; these include crawl spaces, garage corners and window wells. While Widows can be potentially hazardous, they are not an aggressive species. The Widow will only bite a human if disturbed or provoked.
Black Widows can normally be easily identified. The female has a distinct reddish-orange hourglass (or double triangle) shape design on the underside of the abdomen. Colorado State notes that mature females are black, whereas some of the immature females and males may have red, brown or white markings on their backs. According to DesertUSA, these immature Widow spiders do not pose a danger to humans.