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Northeast · NH
When does flea season start in New Hampshire?
Flea season in New Hampshire typically runs mid-April to late October, with the heaviest pressure Jun–Sep. Outside that window outdoor fleas slow down — they don't disappear.
The New Hampshire flea picture
Flea season in New Hampshire is compact: little stirs outdoors before mid-April, the June-through-September stretch does most of the damage, and by late October the cold — January here averages about 24°F — has ended it. Concord and Manchester sit in the milder southern tier, where the season runs a bit fuller than it does up in the White Mountains. The catch is that fleas overwinter beautifully in heated houses, so New Hampshire vets are firm about keeping dogs protected even with snow on the ground.
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 New Hampshire
| Month | Typical pressure | Average temperature |
|---|---|---|
| January | Quiet | 24°F |
| February | Quiet | 26.5°F |
| March | Quiet | 35°F |
| April | Low | 46.8°F |
| May | Moderate | 57.8°F |
| June | Peak | 66.9°F |
| July | Peak | 72.4°F |
| August | Peak | 70.9°F |
| September | High | 62.9°F |
| October | Moderate | 50.8°F |
| November | Quiet | 40.1°F |
| December | Quiet | 29.9°F |
Estimates from NOAA U.S. Climate Normals (1991–2020), averaged across 2 weather stations near New Hampshire'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 New Hampshire — check the city closest to you:
Ticks are a different calendar. In New Hampshire tick activity typically runs late March to late November — see the New Hampshire tick season page.
Frequently asked questions
When does flea season start in New Hampshire?
Around mid-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 New Hampshire?
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 New Hampshire?
Yes — veterinary organizations recommend year-round prevention everywhere, New Hampshire 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 New Hampshire?
Ticks run on their own, earlier calendar — in New Hampshire that's late March to late November. See the New Hampshire tick season page for the month-by-month picture and the species involved.