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Midwest · MO
When does flea season start in Missouri?
Flea season in Missouri typically runs late March to mid-November, with the heaviest pressure May–Sep. Outside that window outdoor fleas slow down — they don't disappear.
The Missouri flea picture
Missouri is warm and humid enough to give fleas a five-month plateau — May through September all run at full strength — inside a season that stretches from late March into mid-November. Yard conditions vary more than the statewide averages suggest: shaded Ozark hollows near Springfield hold moisture much longer than mowed suburban lots in Kansas City, St. Louis or Columbia, and that moisture is what flea larvae live on. Indoors, fleas keep their own calendar; a warm house in December suits them as well as a warm July yard, which is why Missouri veterinarians treat prevention as a year-round commitment.
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 Missouri
| Month | Typical pressure | Average temperature |
|---|---|---|
| January | Quiet | 31.5°F |
| February | Quiet | 36°F |
| March | Low | 46°F |
| April | Moderate | 56.1°F |
| May | Peak | 65.6°F |
| June | Peak | 74.6°F |
| July | Peak | 78.7°F |
| August | Peak | 77.3°F |
| September | Peak | 69.2°F |
| October | Moderate | 57.5°F |
| November | Low | 45.2°F |
| December | Quiet | 35.4°F |
Estimates from NOAA U.S. Climate Normals (1991–2020), averaged across 4 weather stations near Missouri'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 Missouri — check the city closest to you:
Ticks are a different calendar. In Missouri tick activity typically runs mid-February to early December — see the Missouri tick season page.
Frequently asked questions
When does flea season start in Missouri?
Around late March 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 Missouri?
Outdoor flea pressure typically fades around mid-November, 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 Missouri?
Yes — veterinary organizations recommend year-round prevention everywhere, Missouri 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 Missouri?
Ticks run on their own, earlier calendar — in Missouri that's mid-February to early December. See the Missouri tick season page for the month-by-month picture and the species involved.