FleaDates › Tick season › Colorado
Mountain West · CO
When are ticks active in Colorado?
Ticks in Colorado are typically active late February to late November, heaviest May–Sep — and one warm spell can wake them well ahead of spring.
Ticks to know in Colorado
The Rocky Mountain wood tick is the one to know here, out with the first warm spells in the foothills and building from March to a June-through-September high. Colorado is not Lyme country — the blacklegged tick is not established in the state — but Colorado tick fever and Rocky Mountain spotted fever are real local concerns, and American dog ticks share the same grassy edges. Dogs that range through scrub oak and sagebrush at mid-elevation pick up the most, so run your hands over them at the trailhead before you load up.
Wherever the calendar sits this month, the habit that actually catches ticks is the after-walk check: ears, collar line, armpits, between the toes. Prevention plus checks beats either alone.
Month-by-month tick activity in Colorado
| Month | Typical activity | Average temperature |
|---|---|---|
| January | Quiet | 30.4°F |
| February | Low | 33.8°F |
| March | Moderate | 42.6°F |
| April | Moderate | 49.1°F |
| May | High | 58.8°F |
| June | Peak | 69.5°F |
| July | Peak | 75.6°F |
| August | Peak | 73.1°F |
| September | Peak | 65°F |
| October | Moderate | 51.7°F |
| November | Low | 39.5°F |
| December | Quiet | 30.4°F |
Estimates from NOAA U.S. Climate Normals (1991–2020), averaged across 3 weather stations near Colorado's larger cities, using the ~40°F activity threshold reported in published tick research. Real years run early or late with the weather.
Fleas peak later. Colorado flea season typically runs mid-April to late October — see the Colorado flea season page.
Frequently asked questions
When does tick season start in Colorado?
Around late February in a typical year, once temperatures clear roughly 40°F — noticeably earlier than flea season. A February thaw can bring ticks out ahead of schedule.
What ticks live in Colorado?
The species dog owners most often meet in Colorado: Rocky Mountain wood tick, American dog tick, brown dog tick. The Rocky Mountain wood tick is the one to know here, out with the first warm spells in the foothills and building from March to a June-through-September high. Colorado is not Lyme country — the blacklegged tick is not established in the state — but Colorado tick fever and Rocky Mountain spotted fever are real local concerns, and American dog ticks share the same grassy edges. Dogs that range through scrub oak and sagebrush at mid-elevation pick up the most, so run your hands over them at the trailhead before you load up.
Do I need tick prevention in winter in Colorado?
Yes. Ticks overwinter under leaf litter and snow rather than dying off, and mild spells wake them — which is why veterinary organizations recommend year-round parasite prevention. The calendar shows when pressure peaks, not when protection can lapse.
What about fleas in Colorado?
Fleas run on a warmer calendar — in Colorado that's mid-April to late October. See the Colorado flea season page for that month-by-month picture.