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When does flea season start in Delaware?
Flea season in Delaware typically runs late March to mid-November, with the heaviest pressure May–Oct. Outside that window outdoor fleas slow down — they don't disappear.
The Delaware flea picture
Delaware winters are cold enough — mid-30s averages in January and February — to shut down outdoor flea activity for a genuine stretch. The season builds through spring and runs hardest from June through September, when humid Atlantic air settles over Wilmington and Dover alike. Fleas riding out the cold in carpets and dog beds never notice the freeze outside, so year-round prevention remains the standing advice from Delaware vets.
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 Delaware
| Month | Typical pressure | Average temperature |
|---|---|---|
| January | Quiet | 34.8°F |
| February | Quiet | 36.9°F |
| March | Low | 44.1°F |
| April | Moderate | 54.7°F |
| May | High | 64°F |
| June | Peak | 72.9°F |
| July | Peak | 77.8°F |
| August | Peak | 76°F |
| September | Peak | 69.5°F |
| October | High | 58.2°F |
| November | Low | 47.7°F |
| December | Quiet | 39.3°F |
Estimates from NOAA U.S. Climate Normals (1991–2020), averaged across 2 weather stations near Delaware'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 Delaware — check the city closest to you:
Ticks are a different calendar. In Delaware tick activity typically runs mid-February to mid-December — see the Delaware tick season page.
Frequently asked questions
When does flea season start in Delaware?
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 Delaware?
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 Delaware?
Yes — veterinary organizations recommend year-round prevention everywhere, Delaware 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 Delaware?
Ticks run on their own, earlier calendar — in Delaware that's mid-February to mid-December. See the Delaware tick season page for the month-by-month picture and the species involved.