Last checked November 3, 2026 against official sources.
This page lists 8 spiders. 1 is venomous by official accounts, and 2 mildly venomous. 2 are nonnative.
University of Idaho Extension says: “Though all other spiders have venom, the percentage that are actually dangerous to humans is very small.” Official sources name Western Black Widow as dangerous to people; it is marked venomous, with the source, and listed first. The other 5 spiders are marked “Not named as dangerous”. That does not make them harmless: do not handle spiders.
Not every species: no complete official list of Idaho spiders exists, so this page covers the ones state and Extension sources name. How lists are built.
Official sources single out these spiders in Idaho, in their own words:
Venomous. “…there is only one arachnid in Idaho that is considered medically important to humans (i.e., possesses dangerous venom), the black widow spider” University of Idaho Extension
Venomous species first, then A to Z. Do not handle them.
Latrodectus hesperus
Venom: “In Idaho, only one native spider is dangerous to humans, the western black widow (Latrodectus hesperus)” (University of Idaho Extension)
Cheiracanthium inclusum
Venom: “…they are thought to be mildly venomous” (University of Idaho Extension)
Cheiracanthium mildei
Venom: “…they are thought to be mildly venomous” (University of Idaho Extension)
Phidippus audax
Araneus gemmoides
Steatoda triangulosa
Pholcus phalangioides
Eratigena agrestis
Records of spiders in Idaho peak in May to July and 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.
Official advice from University of Idaho Extension:
Invasive species: Idaho Invasive Species Hotline 1-877-336-8676 (ISDA). Wildlife crimes: Citizens Against Poaching 1-800-632-5999 (IDFG). Bear sightings and conflicts: report to the state wildlife agency (IDFG regional offices). Idaho State Department of Agriculture
Yes. UI Extension: the western black widow is the only native Idaho spider dangerous to humans; it occurs statewide and is most common in the southern third. University of Idaho Extension
“Latrodectus occur statewide but are most common in the southern third.”
No. UI Extension: the brown recluse is not native to Idaho and there are no verified cases from Idaho; one found would likely have been carried in from its native range. University of Idaho Extension
“No verified cases of brown recluse spiders are known from Idaho.”
The species list comes from No official complete list; commonly encountered and medically important species from UI Extension BUL 1094 (Homeowner Guide to Idaho’s Arachnids, 2025) (University of Idaho Extension, September 1, 2025).
Venom labels come only from official sources and link to them; "Not stated" never means harmless. How labels work.
"Nonnative" and "Invasive" follow the wording of the source list. See invasive species in Idaho.
“In Idaho, only one native spider is dangerous to humans, the western black widow (Latrodectus hesperus)”
“…there is only one arachnid in Idaho that is considered medically important to humans (i.e., possesses dangerous venom), the black widow spider”
“Though all other spiders have venom, the percentage that are actually dangerous to humans is very small.”
“…they are thought to be mildly venomous”
“If you think you have or someone else has been bitten by a black widow, seek IMMEDIATE medical attention.”
“People usually notice hobo spiders as lone specimens running across ground-level floors inside homes from mid-July through the first killing fall frost”
“Latrodectus occur statewide but are most common in the southern third.”
“No verified cases of brown recluse spiders are known from Idaho.”
“Idaho Invasive Species Hotline [toll-free]: 1-877-336-8676”
