Brown recluse spider, Loxosceles reclusa 

Order: Araneae
Family: Sicariidae


The brown recluse spider is uncommon and frequently misidentified in Colorado. These spiders can have light or dark brown bodies and are about the size of a quarter with legs extended. One distinguishing feature of this species is the violin-shaped mark on the back of the cephalothorax, the body segment that contains the head and legs. The legs of the brown recluse spider are very long, not banded, and are thought to have a silky appearance since large hairs are not present. The egg sac is less than 2.5 cm (1 inch) in diameter and contain about 40-50 small yellow eggs. Incidences in Colorado typically result from unintentional transport of brown recluse spiders from infested areas.

In Colorado, funnel weaver spiders, cellar spiders, and wolf spiders are commonly mistaken for brown recluse spiders. However, unlike most spiders in Colorado, brown recluse spiders have three pairs of eyes instead of four. More information on spiders commonly found in Colorado homes is available here.

Quick Facts

  • In the United States, there are ten spiders in the genus Loxosceles. Most species are confined to southwestern states that border Mexico. They can live outdoors under rocks, logs, woodpiles, and debris, or in dark areas of the home such as basements.
  • Brown recluse spiders are very rare in Colorado. Funnel weaver spiders, cellar spiders, and wolf spiders are commonly misidentified as brown recluse spiders. Two important distinguishing features of brown recluse spiders are the three pairs of eyes and characteristic violin marking on the back.
  • Reducing clutter in the house will limit the number of hiding places for brown recluse spiders. Further management is not typically necessary in Colorado.
bed bug infestation

Adult brown recluse spider. Notice the violin-shaped markings on back. Image credit: Lisa Ames, Univeristy of Georgia,

bed bug bites

Adult brown recluse spider. Notice the violin-shaped markings on back. Image credit: Lisa Ames, Univeristy of Georgia,

bed bug eggs

Adult brown recluse spider. Image credit: Lisa Ames, University of Georgia,

bed bug eggs

Bite inflicted by a brown recluse spider. Note the sunken appearance of the blister. Image credit: USDA Forest Service – Coeur d’Alene Field Office,

Life history and habits

The immature spider reaches adulthood about a year after hatching and lives one to three years as an adult. After laying eggs, female spiders guard egg sacs until they hatch after one month. The spiderlings undergo five molts before developing into adults. An individual brown recluse spider can live two to four years and can live up to six months during periods of extreme drought or when food is absent.

Outdoors, brown recluse spiders live under rocks, logs, in wood piles, or other protective areas. They actively hunt at night and do not use webs to capture prey. In homes, brown recluse spiders like to live in dark, undisturbed areas such as basements, sheds, or garages. They are not active during the day and will hide in their webs in dark areas.

Brown recluse spiders have venom that causes tissue death, but the amount of venom introduced during the bite is controlled by the spider. The venom’s toxicity varies between species.


It is impossible to diagnose a brown recluse spider bite from the wound alone, as many medical conditions produce similar necrotic-looking sores. Bites inflicted by the brown recluse spider are initially painless until several hours later when the affected area becomes red, swollen, and tender. In most cases, the bite will heal in several weeks with no further medical intervention. In more extreme cases, a necrotic lesion with a dry, sinking blue patch, central blister, and irregular edges may develop and expand several inches over days or weeks. The ulcer can persist for several months and leave a deep scar. Severe reactions to brown recluse bites tend to occur in children, the elderly, or individuals in poor health. When bitten by a brown recluse spider, it is recommended to apply ice, elevate the affected area, and seek medical attention immediately.


Any dark, undisturbed area can harbor brown recluse spiders, and reducing clutter will limit the number of hiding places. Further management is typically not required in Colorado where brown recluse spiders are extremely rare.


Hu, X. 2022. The Brown Recluse Spider: Facts and Control. Alabama A&M Extension. Available,300%20eggs%20during%20the%20summer.

Potter, M. 2018 Brown Recluse Spider. University of Kentucky – Entomology. Available,size%20of%20a%20U.S.%20quarter.

CSU Extension Fact Sheet

Download or view the CSU Extension’s PDF fact sheet for your reference.