Notable concerns
- Western black widow
- Hobo spider
Medically significant species in Idaho
| Species | Scientific | Significance | Range note |
|---|---|---|---|
| Western Black Widow | Latrodectus hesperus | Medically significant | Western North America from southern British Columbia south to Mexico, east to the Great Pl |
| Yellow Sac Spider | Cheiracanthium inclusum | Moderate | Throughout the continental United States and southern Canada. |
All documented species in this index
Species below are present in Idaho according to extension publications and the rangeStates records in our species index. Click through for full profiles.
- Western Black Widow - Latrodectus hesperus (Medically significant)
- Hobo Spider - Eratigena agrestis (Low)
- Yellow Sac Spider - Cheiracanthium inclusum (Moderate)
- Common House Spider - Parasteatoda tepidariorum (Low)
- Wolf Spider - Lycosidae (family overview) (Low)
- Cellar Spider - Pholcus phalangioides (Not medically significant)
- Bold Jumping Spider - Phidippus audax (Low)
- Yellow Garden Spider - Argiope aurantia (Not medically significant)
- Grass Spider - Agelenopsis spp. (Not medically significant)
Seasonal activity in Idaho
Spider activity in Idaho follows the documented peak season of May–September. Indoor sightings often spike in late summer and early fall as males wander to find mates and as cooling outdoor temperatures push synanthropic species toward heated structures.
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Highlighted months reflect the state extension peak-activity window. Individual species (especially indoor recluse populations) may be active outside this range.
Prevention checklist for Idaho homes
- Seal exterior gaps wider than 1/8 inch around utility penetrations, dryer vents, and weep holes. Install door sweeps on garage and basement entries.
- Reduce harborage by storing firewood, lumber, and seldom-used boxes off the ground and at least 18 inches from foundation walls.
- For widow-active areas, wear gloves when handling outdoor electrical boxes, irrigation valves, and stacked materials. Widows favor undisturbed voids.
- Vacuum webs, egg sacs, and spiders rather than spraying. Mechanical removal outperforms most over-the-counter residual sprays for synanthropic species.
If you are bitten
Nearby states in the Mountain region
- Spiders of Colorado - peak activity may–september
- Spiders of Montana - peak activity june–august
- Spiders of Utah - peak activity april–october
- Spiders of Wyoming - peak activity june–august
Sources
- [1]Idaho spider identification - Idaho Cooperative Extension. Accessed 2026-06-14.
- [2]Spiders and scorpions submitted as suspected brown recluse - Vetter RS, 2008. Accessed 2026-06-14.