FleaDates › Flea season › Colorado › Denver
Denver · CO
When does flea season start in Denver?
Flea season in Denver typically runs mid-April to late October, peaking Jun–Sep.
Ticks in Denver
Local tick activity typically runs early March to late November, heaviest May–Sep. The species to know in Colorado: Rocky Mountain wood tick, American dog tick, brown dog tick.
More on species and timing: Colorado tick season.
Numbers come from NOAA U.S. Climate Normals (1991–2020) recorded at DENVER INTL AP — a climate-based estimate; real years wobble.
Frequently asked questions
When does flea season start in Denver?
Around mid-April in a typical year, once local averages hold around 50°F. A warm spring pulls it earlier — prevention shouldn't wait for the calendar.
Is flea season in Denver different from the rest of Colorado?
Not meaningfully — Denver tracks the Colorado statewide estimate closely. Both are climate-based estimates, so treat the edges as fuzzy, not exact.
Do dogs in Denver need prevention outside flea season?
Yes — vets recommend year-round parasite prevention regardless of the local calendar. Indoor fleas ignore the weather entirely, and ticks in Colorado are typically active late February to late November, a longer window than fleas get.