The brown recluse spider (Loxosceles reclusa) is one of the few North American spiders with venom that can cause serious medical concern. Its necrotic venom, which potentially damages skin tissue, makes accurate identification a priority for people encountering small brown spiders. Understanding the geographic distribution of the species is key, as many reported bites are ultimately misdiagnosed or caused by other issues. This article details where the brown recluse resides and how to identify it from harmless look-alikes.
Natural Range of the Brown Recluse
The definitive answer to whether the brown recluse is established in Colorado is no, as the state lies well outside the spider’s natural range. This species is primarily limited to the South-Central Midwest of the United States, extending from Nebraska down through Texas and across to western Georgia and Kentucky. The environmental conditions in Colorado, particularly the high elevation and dry climate, are generally unsuitable for the establishment of a sustained population.
While there is no established population in Colorado, isolated instances of the spider being transported into the state do occur, though rarely. These individual spiders are usually accidental imports, hitchhiking in moving boxes, furniture, or freight from native states. A few specimens have been confirmed in Colorado over the decades, but these isolated finds do not indicate a breeding or self-sustaining presence. For the vast majority of Colorado residents, any encounter with a brown spider will involve a native species rather than an imported recluse.
Spiders in Colorado Often Mistaken for Recluses
Because the brown recluse is so rare in Colorado, most suspected sightings involve one of the state’s many harmless brown spiders. One frequent culprit is the Funnel Weaver Spider, a group that includes the Hobo Spider. Funnel weavers are brown, hairy, and build distinct sheet-like webs that terminate in a funnel-shaped retreat. These webs are often visible in lawns, rock piles, or building corners. Funnel weavers possess eight eyes arranged in two rows, a distinct difference from the recluse, and they are not considered a medical threat.
Cellar Spiders and Wolf Spiders are also often confused with the recluse. Cellar spiders, often called “daddy-long-legs,” have extremely long legs and a distinct body shape, but their light brown coloration can cause misidentification. Wolf spiders are robust, fast-moving hunters that do not build webs to catch prey. They are often brown or gray with patterns and possess eight eyes. Unlike the recluse, which has smooth legs, both funnel weavers and wolf spiders have legs covered in noticeable spines and hairs.
Key Features for Identifying a Brown Recluse
Identifying a brown recluse requires focusing on specific anatomical markers, since many other spiders are brown. The most reliable feature is the spider’s eye arrangement, which is only visible under magnification. Unlike most spiders that have eight eyes in two rows, the brown recluse has only six eyes arranged in three pairs (dyads) in a semicircle on its cephalothorax.
The spider is known for the dark, violin-shaped marking on the top of its cephalothorax, with the neck pointing toward the abdomen. While this pattern is characteristic, it is not exclusive, as other spiders can have similar markings. The violin mark must be present and accompanied by other features, such as uniformly colored, spineless legs. The abdomen also lacks any stripes, spots, or other patterns.
What to Do If Bitten by a Suspicious Spider
If a bite from any spider is suspected, the immediate focus should be on basic first aid. Gently clean the bite site with mild soap and water to prevent secondary bacterial infection. Applying a cold compress or an ice pack wrapped in a cloth can help to reduce swelling and manage localized pain. If the bite is on an arm or leg, keeping the limb elevated can also help to minimize swelling.
Monitor the bite closely, as most spider bites, even those from a brown recluse, are minor and heal without severe complications. Seek medical attention immediately if systemic symptoms develop, such as fever, chills, nausea, or body aches. Consult a physician if the wound shows signs of severe infection, such as rapidly spreading redness, increased warmth, or a worsening open sore. Bringing the spider, if safely captured, or a clear photograph can help medical professionals confirm the identity and determine the appropriate course of treatment.