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Mountain West · WY
When does flea season start in Wyoming?
Flea season in Wyoming typically runs early May to mid-October, with the heaviest pressure Jun–Sep. Outside that window outdoor fleas slow down — they don't disappear.
The Wyoming flea picture
Few states start later than Wyoming: the flea window does not open until early May and it is closed again by mid-October, with June and September busy and July and August at the top. Cheyenne, Casper and Sheridan all sit high and wind-scoured, and that dry air is genuinely rough on flea eggs — outdoors. Indoors is a different building altogether, where a warm floor and a favorite dog bed can sustain a small infestation straight through a Wyoming winter, so a short outdoor season is not a reason to pause prevention.
One thing that's true in every state: indoor fleas are year-round everywhere. A heated house in January is a fine flea nursery, which is why the calendar above describes outdoor pressure — not whether fleas are possible.
Month-by-month flea pressure in Wyoming
| Month | Typical pressure | Average temperature |
|---|---|---|
| January | Quiet | 26.1°F |
| February | Quiet | 27.4°F |
| March | Quiet | 36.2°F |
| April | Low | 42.8°F |
| May | Moderate | 52.2°F |
| June | High | 62.5°F |
| July | Peak | 70.6°F |
| August | Peak | 68.7°F |
| September | High | 59.2°F |
| October | Low | 45.7°F |
| November | Quiet | 34.5°F |
| December | Quiet | 26°F |
Estimates from NOAA U.S. Climate Normals (1991–2020), averaged across 3 weather stations near Wyoming's larger cities, with activity thresholds from published veterinary and entomology research. Real years run early or late with the weather.
Flea season near you
Climate shifts even within Wyoming — check the city closest to you:
Ticks are a different calendar. In Wyoming tick activity typically runs late March to early November — see the Wyoming tick season page.
Frequently asked questions
When does flea season start in Wyoming?
Around early May in a typical year, once average temperatures hold around 50°F — the point where fleas begin reproducing in earnest outdoors. Warm springs pull that earlier, which is a good argument for not waiting.
When does flea season end in Wyoming?
Outdoor flea pressure typically fades around mid-October, when sustained cold shuts down reproduction outside. Indoors is another story — heated homes stay flea-friendly all winter.
Does my dog need flea prevention in winter in Wyoming?
Yes — veterinary organizations recommend year-round prevention everywhere, Wyoming included. Fleas overwinter indoors on pets and in bedding regardless of the weather outside, and a warm snap can restart outdoor activity early. The season calendar tells you when to be extra vigilant, not when to stop.
What about ticks in Wyoming?
Ticks run on their own, earlier calendar — in Wyoming that's late March to early November. See the Wyoming tick season page for the month-by-month picture and the species involved.