Snakes and spiders in Boulder County, Colorado
Boulder County, home of Boulder, has 11 snake and 79 spider species on record, from 336 licensed snake and 605 spider records. Venomous species here: the prairie rattlesnake and the western black widow.
Are there venomous snakes or spiders in Boulder County?
Yes. The prairie rattlesnake: 41 licensed records, 3% of all Colorado records of it. The western black widow: 23 licensed records, 14% of all Colorado records of it.
What snakes are in Boulder County?
In all, 11 snake species are on the Boulder County list. The most recorded are the western terrestrial garter snake (85), the gopher snake (66) and the plains garter snake (60).
| # | Species | Records | Share of Colorado records |
|---|---|---|---|
| 1 | Western terrestrial garter snake Thamnophis elegans | 85 | 10% |
| 2 | Gopher snake Pituophis catenifer | 66 | 18% |
| 3 | Plains garter snake Thamnophis radix | 60 | 23% |
| 4 | Prairie rattlesnake venomous Crotalus viridis | 41 | 3% |
| 5 | Eastern racer Coluber constrictor | 37 | 30% |
| 6 | Common garter snake Thamnophis sirtalis | 19 | 17% |
| 7 | Northern water snake Nerodia sipedon | 12 | 29% |
| 8 | Central plains milksnake Lampropeltis gentilis | 9 | 31% |
| 9 | Lined snake Tropidoclonion lineatum | 4 | 19% |
| 10 | Plains black-headed snake Tantilla nigriceps | 1 | 8% |
| 11 | Smooth green snake Opheodrys vernalis | 1 | 5% |
When are snakes out in Boulder County?
Observation records of snakes in Boulder County run mostly May through October, peaking in May with 23% of them, the same peak as Colorado as a whole.
What spiders are in Boulder County?
In all, 79 spider species are on the Boulder County list. The most recorded are the bold jumper (97), Dysdera crocata (54) and the Asian wall jumper (34). Boulder County holds more than half of all Colorado records of the common candy-striped spider, the hobo spider, the parson spider and Pholcophora americana.
| # | Species | Records | Share of Colorado records |
|---|---|---|---|
| 1 | Bold jumper Phidippus audax | 97 | 14% |
| 2 | Dysdera crocata | 54 | 49% |
| 3 | Asian wall jumper Attulus fasciger | 34 | 13% |
| 4 | Zebra spider Salticus scenicus | 32 | 8% |
| 5 | Barn funnel weaver Tegenaria domestica | 29 | 45% |
| 6 | Apache jumping spider Phidippus apacheanus | 27 | 15% |
| 7 | Western black widow venomous Latrodectus hesperus | 23 | 14% |
| 8 | Common candy-striped spider Enoplognatha ovata | 20 | 77% |
| 9 | Triangulate bud spider Steatoda triangulosa | 20 | 41% |
| 10 | Hobo spider Eratigena agrestis | 17 | 59% |
| 11 | Banded garden spider Argiope trifasciata | 14 | 31% |
| 12 | Habronattus cuspidatus | 11 | 10% |
| 13 | Parson spider Herpyllus ecclesiasticus | 11 | 65% |
| 14 | Pholcophora americana | 8 | 80% |
| 15 | Brilliant jumping spider Phidippus clarus | 7 | 37% |
| 16 | Cat-faced spider Araneus gemmoides | 7 | 25% |
| 17 | Goldenrod crab spider Misumena vatia | 7 | 12% |
| 18 | Proszynski's jumping spider Evarcha proszynskii | 7 | 54% |
| 19 | Carolina wolf spider Hogna carolinensis | 6 | 29% |
| 20 | California flattened jumping spider Platycryptus californicus | 5 | 17% |
| 21 | Dock spider Dolomedes scriptus | 5 | 33% |
| 22 | Filmy dome spider Neriene radiata | 5 | 83% |
| 23 | Peppered jumper Pelegrina galathea | 5 | 14% |
| 24 | Spotted orbweaver Neoscona crucifera | 5 | 31% |
| 25 | Buttonhook leafbeetle jumping spider Sassacus vitis | 4 | 31% |
| 26 | Drumming sword wolf spider Gladicosa gulosa | 4 | 67% |
| 27 | Pelegrina aeneola | 4 | 5% |
| 28 | Zelotes fratris | 4 | 50% |
| 29 | Attinella dorsata | 3 | 16% |
| 30 | Cone-shaped orbweaver Cyclosa conica | 3 | 60% |
| 31 | Habronattus altanus | 3 | 6% |
| 32 | Neglected ground hunter spider Drassodes neglectus | 3 | 38% |
| 33 | Gnaphosa muscorum | 2 | 40% |
| 34 | Longbodied cellar spider Pholcus phalangioides | 2 | 40% |
| 35 | McCook's split wolf spider Schizocosa mccooki | 2 | 10% |
| 36 | Phidippus octopunctatus | 2 | 40% |
| 37 | Sixspotted orbweaver Araniella displicata | 2 | 6% |
| 38 | Tigrosa grandis | 2 | 33% |
| 39 | Attinella juniperi | 1 | 100% |
| 40 | Carolina jumping spider Phidippus carolinensis | 1 | 17% |
| 41 | Four-lined slender jumping spider Marpissa lineata | 1 | 100% |
| 42 | Glossy ant-spider Micaria pulicaria | 1 | 50% |
| 43 | Greater ant-mimic corinne spider Phrurotimpus borealis | 1 | 100% |
| 44 | Long-jawed orb weaver Tetragnatha laboriosa | 1 | 17% |
| 45 | Mackenzie's thin-legged wolf spider Pardosa mackenziana | 1 | 50% |
| 46 | Northern yellow sac spider Cheiracanthium mildei | 1 | 50% |
| 47 | Oblong running spider Tibellus oblongus | 1 | 33% |
| 48 | Pardosa concinna | 1 | 20% |
| 49 | Pardosa sternalis | 1 | 8% |
| 50 | Pennsylvania grass spider Agelenopsis pennsylvanica | 1 | 100% |
| 51 | Steatoda albomaculata | 1 | 20% |
| 52 | Thanatus coloradensis | 1 | 100% |
| 53 | Western lynx spider Oxyopes scalaris | 1 | 9% |
| 54 | Wetland giant wolf spider Tigrosa helluo | 1 | 17% |
| 55 | Zelotes lasalanus | 1 | 50% |
| 56 | Zelotes puritanus | 1 | 20% |
| 57 | Diplostyla concolor | — | — |
| 58 | Forest wolf spider Hogna frondicola | — | — |
| 59 | Grammonota gentilis | — | — |
| 60 | Groenland wolf spider Pardosa groenlandica | — | — |
When are spiders out in Boulder County?
Observation records of spiders in Boulder County run mostly March through October, peaking in July with 20% of them; across Colorado the peak is August.
What stands out in Boulder County
Species for which Boulder County holds a large share of all Colorado records: the common candy-striped spider, 77% (20 of 26); the hobo spider, 59% (17 of 29); Dysdera crocata, 49% (54 of 111); the barn funnel weaver, 45% (29 of 64); the triangulate bud spider, 41% (20 of 49); the banded garden spider, 31% (14 of 45); the eastern racer, 30% (37 of 123); the northern water snake, 29% (12 of 42).
Common in Colorado, not on the Boulder County list
Among the snakes most recorded across Colorado, these do not reach the county list: the coachwhip (58 statewide), the western rattlesnake (47 statewide), the plains hog-nosed snake (45 statewide), the western ground snake (36 statewide) and the glossy snake (33 statewide). Few records here can mean the species is rare in the county, or that few people have looked.
Among the spiders most recorded across Colorado, these do not reach the county list: the Texas brown tarantula (71 statewide). Few records here can mean the species is rare in the county, or that few people have looked.
Harmless lookalikes in Boulder County
No copperheads reach the county list, and GBIF holds no copperhead record for Colorado under any license, so one reported here is most likely a harmless lookalike: the northern water snake and the central plains milksnake. No cottonmouths reach the county list, and GBIF holds no cottonmouth record for Colorado under any license, so one reported here is most likely a harmless lookalike: the northern water snake. Rattlesnakes are on the county list, and so are harmless species often taken for them: the gopher snake. No coral snakes reach the county list, and GBIF holds no coral snake record for Colorado under any license, so one reported here is most likely a harmless lookalike: the central plains milksnake. Widow spiders are on the county list, and so are harmless species often taken for them: the triangulate bud spider. Recluse spiders are not on the Colorado list, but GBIF holds 20 recluse spider records of any license in Colorado (brown recluse 18, Apache recluse 2), 1 of them in Boulder County: treat any spider like this as venomous until identified. Harmless species often taken for them here: the hobo spider, the longbodied cellar spider and the Pennsylvania grass spider.
Boulder County among Colorado counties
By licensed snake records Boulder County ranks 2nd of 63 Colorado counties with any.
Other Colorado counties with their own page: Weld County, Larimer County and El Paso County.
The whole state: venomous species in Colorado, all snakes, all spiders.
GBIF records read 2026-09-29. Listed: any license. Counted: CC0/CC BY only. How we count.