Last checked November 3, 2026 against official sources.
This page lists 13 spiders and 2 other arachnids. 2 are venomous by official accounts, and 1 mildly venomous.
Not every species: no complete official list of Colorado spiders exists, so this page covers the ones state and Extension sources name. How lists are built.
Official sources single out these spiders in Colorado, in their own words:
Venomous. “All members of the genus Latrodectus are potentially harmful to humans.” Colorado State University Extension
Official sources say the brown recluse is not native to Colorado or not found there. It is not counted on this page; each entry quotes the source.
Not native. “Funnel web spiders are harmless but are often mistaken for the brown recluse, a spider whose venom is of medical importance, that does not naturally occur in Colorado.” Colorado State University Extension
It is venomous, per Colorado State University Extension. If you find one, do not touch it.
Venomous species first, then A to Z. Do not handle them.
Latrodectus hesperus
Venom: “Bites from the widow spider are painful and potentially dangerous because they contain a nerve venom.” (Colorado State University Extension)
Habitat: They usually build their webs near the ground in dark, undisturbed sites. (Colorado State University Extension)
Dysdera crocata
Venom: “Their bite can be painful but they are not aggressive and their venom is not known to cause medical problems.” (Colorado State University Extension)
Venom: “Cellar spiders can bite humans (rarely), but the venom rarely causes more than mild irritation (if any symptoms occur at all).” (Colorado State University Extension)
Argiope trifasciata
Araneus gemmoides
Steatoda triangulosa
Order Opiliones
Venom: “Unlike spiders, daddy-long-legs do not possess venom glands, nor do they produce silk.” (Colorado State University Extension)
Loxosceles rufescens
Aphonopelma vogelae
Aphonopelma hentzi
Cheiracanthium spp.
Order Solifugae
Venom: “They possess large conspicuous jaws used to crush prey, but they do not have venom glands.” (Colorado State University Extension)
Aphonopelma spp.
Records of spiders in Colorado peak in June to September. They show when people record spiders, not how many there are (about month bars).
Call 911 or Poison Help at 1-800-222-1222 right away. Poison Help connects you to your local poison center, any time of day.
Invasive species: file a report with CPW (online "Report a Sighting" form linked from cpw.state.co.us/invasive-wildlife). Injured/abandoned animals, feeding or illegal activity: CPW Denver Headquarters 303-297-1192 or any CPW office; anonymous: Operation Game Thief 877-265-6648. After-hours emergency: Colorado State Patrol 303-239-4500. Wildlife posing immediate danger: local CPW office or law enforcement. Colorado Parks and Wildlife
Yes. CSU Extension says widow spiders, particularly the western widow, are common in Colorado. Colorado State University Extension
“Widow spiders, particularly the western widow (Latrodectus hesperus), are common in Colorado.”
The species list comes from No complete official list of Colorado spiders. Entries are medically significant and commonly asked spiders named by CSU Extension (Spiders in the Home 5.512; Western Widow Spider; Brown Recluse Spiders in Colorado; Colorado Tarantulas) (Colorado State University Extension, Reviewed August 2025). 4 more entries come from other official sources named on each card.
Venom labels come only from official sources and link to them; "Not stated" never means harmless. How labels work.
“Bites from the widow spider are painful and potentially dangerous because they contain a nerve venom.”
“Their bite can be painful but they are not aggressive and their venom is not known to cause medical problems.”
“They possess large conspicuous jaws used to crush prey, but they do not have venom glands.”
“Unlike spiders, daddy-long-legs do not possess venom glands, nor do they produce silk.”
“Funnel web spiders are harmless but are often mistaken for the brown recluse, a spider whose venom is of medical importance, that does not naturally occur in Colorado.”
“The venom of the brown recluse is damaging to human cells.”
“Funnel web spiders are the most common spiders found in homes, particularly during late summer and early fall.”
“They occasionally enter buildings, particularly in early summer.”
“Widow spiders, particularly the western widow (Latrodectus hesperus), are common in Colorado.”
“All members of the genus Latrodectus are potentially harmful to humans.”
“Cellar spiders can bite humans (rarely), but the venom rarely causes more than mild irritation (if any symptoms occur at all).”
“If you spot any invasive species, file a report with CPW.”
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