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The Spiders in Colorado

Spiders in Colorado must be hardy or resourceful enough to endure very cold winters. Most of the spiders have been there for thousands of years, but some, such as the camel spider, were brought to Colorado as a result of human activity. Colorado has some potentially dangerous spiders, but most of the state's spiders present no danger to humans.

  1. Potentially Dangerous Spiders

    • Although it is non-aggressive and rarely attacks, the widow spider's bite is painful and potentially dangerous because its venom contains a nerve poison. The western widow is the most common of this species in Colorado. The female is black and has the much recognized orange-red hourglass on her underside. Males may be marked with brown, red or white. The brown recluse is rare in Colorado but was brought into the state because it is common along the southern Mississippi Valley. It is recognized by the violin-shaped marking behind its head. The venom of the brown recluse damages human cells. The bite spot may form an ulcerous wound that is slow to heal.

    Garden Spiders

    • Garden variety spiders in Colorado include funnel weavers, wood louse hunters, ground and jumping spiders. Funnel weavers, also known as grass spiders, are the most common in the state, and they are known to invade homes. These are harmless spiders but are sometimes mistaken for the brown recluse, which is rare in Colorado. The wood louse uses its large fangs to feed on pillbugs (roly-polies), which is why it's also known as the roly-poly hunter. Ground spiders are found under rocks and wood in a silk home, which it only leaves when it is time to hunt. The jumping spider, which jumps on its prey, is a brightly colored, big-eyed spider. It lays a trail in silk, covers its eggs and constructs temporary shelters.

    House Spiders

    • Although some garden spiders will wander into a home, usually spiders in the house are cobweb spiders (also called house spiders), cellar spiders or long-legged sac spiders. Cobweb spiders build webs in darker corners of a house. Their webs are messy and sticky. Most are harmless, but one genus, the widow spider (with the orange-red hourglass), is potentially dangerous. Cellar spiders keep to garages, cellars and small crawl spaces. Long-legged sac spiders make their homes in upper corners of a room or in a wall crack. They are very common in the house during fall and are thought to be the most common source of spider bites in houses.

    Large Spiders

    • The largest spider in Colorado is the cat-faced or monkey-faced spider (the Araneus gemmoide). This spider is seen a lot in the state, but it is harmless. The female can reach 1 inch in diameter and has a prominent pair of humps on its back. Wolf spiders are also very large; some species, such as the giant wolf spider, can be mistaken for the tarantula, which is found in southeastern and southwestern Colorado. Wolf spiders will enter a home, especially if the home was built in a place where it disturbed their habitat. Some species of the banded garden spider are also large.

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