What to Know About Two of Colorado's Deadliest Spiders

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There are only two spider species in Colorado that are capable of biting (and harming) humans. Colorado is home to only one of those two species: the Black Widow. However, The Brown Recluse Spider–another lethal-biting spider–is also staking its territory in this state, much to residents' fear for their safety.

Read on to learn and discover more about two of Colorado’s deadliest spiders.

Colorado’s “The Black Widow”

All 31 species of widow spiders are classified as Theridiidae, or comb-footed spiders. Their name derives from a series of hairs on the backs of their hind legs that resemble tiny combs. By weaving irregular cobwebs, widow spiders hunt insects. Their foot combs are used to wrap the silk around their prey. This is why they prefer densely forested areas near the ground that are dark and undisturbed. 

Like the majority of the other 30 widow spider species, the western widow spider is black with a red hourglass pattern on the abdomen. 

Muscle pain, nausea, and diaphragmatic paralysis are all symptoms of the western widow's bite, making breathing difficult. While the majority of widow-bite victims survive unharmed, bites to the elderly or small children can be fatal. If you have been bitten by a widow spider and experience severe symptoms, seek immediate medical attention. 

Western widow spiders, on the other hand, rarely, if ever, bite outside their web. Additionally, they may bite to protect an egg sack contained within the female's web. 

If discovered, destroy and crush the web and spider to bring them under control. Spiders can also be controlled and kept out of your home using insecticides. 

Controlling other insects on your property, such as cockroaches, can assist in eliminating a food source for the widows and preventing them from entering your home. 

Colorado’s “The Brown Recluse Spider”

The brown recluse spider is Colorado's second most lethal spider. Their abdomen is marked with a violin shape, which gives them the common name fiddleback spider. 

Unlike the neurotoxin found in widow spider bites, the venom of the brown recluse spider kills tissue. The initial bite may feel as if it were a pinprick or may go unnoticed entirely. The bite may have no further effect on the victim, depending on the venom dose. A bluish patch may form a few hours after the bite and develop into a blister. This condition may develop into a two-inch irregular lesion. It may take months for the ulcerated area to heal, leaving permanent scarring. 

Fortunately, Colorado's brown recluse is a relatively uncommon species. In the United States, the majority of brown recluse spider species are found in Arizona, New Mexico, Texas, California, and Nevada. 


The most common recluse spider in the United States is the Loxosceles Reclusa, which is found in eastern Kansas, Missouri, Arkansas, Louisiana, Oklahoma, and parts of Texas. Do not be alarmed, because while it is capable of being transported outside of its normal range, it rarely survives and establishes. 

While one or two confirmed specimens have been collected, "their presence in Colorado is (clearly) coincidental, resulting from occasional transfers from chronically infested areas of the country." According to the CSU Extension Office, the establishment and sustained breeding of these spiders in Colorado are extremely rare. 

The Protocol

First, seek medical attention immediately if you believe you have been bitten by one of these dangerous Colorado spiders–the brown recluse or the black widow. However, the best way to truly be proactive and avoid spiders in or around your home is to call professionals today and get the treatment you need.


It may be daunting to know that there are insects that could bite and kill you or someone you know. This is why it’s best to take control of the situation and leave it up to the pros. The faster you act, the more you can prevent encounters with these spiders!

Are you looking for indoor spider control in Denver? Whitmore Pest Control can offer dedicated solutions for the safety of your home. Give us a call today and get your FREE online quote!

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