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Pacific · WA
When does flea season start in Washington?
Flea season in Washington typically runs early April to late October, with the heaviest pressure Jun–Sep. Outside that window outdoor fleas slow down — they don't disappear.
The Washington flea picture
Two Washingtons show up in the monthly means: marine air keeps Seattle soft and damp, Spokane and Yakima swing colder in winter and drier in summer, and the statewide January figure lands in the mid-30s. The result is a flea season with a slow ramp and a concentrated middle, July and August carrying the heaviest pressure with June and September close behind. None of that winter chill reaches the flea living in the warm rug near the woodstove, so year-round prevention stays the standard recommendation even when the yard looks asleep.
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 Washington
| Month | Typical pressure | Average temperature |
|---|---|---|
| January | Quiet | 34.7°F |
| February | Quiet | 37.7°F |
| March | Low | 43.5°F |
| April | Low | 49.5°F |
| May | Moderate | 57.6°F |
| June | High | 63.3°F |
| July | Peak | 70.3°F |
| August | Peak | 69.7°F |
| September | High | 62°F |
| October | Moderate | 50.5°F |
| November | Quiet | 40.2°F |
| December | Quiet | 33.9°F |
Estimates from NOAA U.S. Climate Normals (1991–2020), averaged across 3 weather stations near Washington'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 Washington — check the city closest to you:
Ticks are a different calendar. In Washington tick activity typically runs mid-February to late November — see the Washington tick season page.
Frequently asked questions
When does flea season start in Washington?
Around early April 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 Washington?
Outdoor flea pressure typically fades around late 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 Washington?
Yes — veterinary organizations recommend year-round prevention everywhere, Washington 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 Washington?
Ticks run on their own, earlier calendar — in Washington that's mid-February to late November. See the Washington tick season page for the month-by-month picture and the species involved.