Fig 1 Environmental conditions required for fleas to survive across all life stages.
Cat fleas die outdoors in winter. No life stage can survive in freezing temperatures for extended periods. However, adult fleas will stay alive on their warm-blooded hosts, and immature stages can develop in homes or the freeze-protected dens of wildlife. Cat fleas don’t hibernate, despite what some sources claim.
Fleas Survive Year-Round
Small populations of fleas can be found on domestic and feral animals year-round, even during the coldest months. However, it’s rare for new infestations to begin on dogs and cats during winter. Fleas developing outdoors can’t survive the cold, arid conditions of most temperate zones. Even in California, few fleas are found from January to April.
Some geographic locations have warm, humid climates year-round. In southern Florida, for instance, fleas will continue thriving outdoors through the winter months of November to March.
Don’t Stop Treatments in Winter
The changing of the seasons won’t end a current flea infestation. Stopping flea treatments in cool months is a common cause for reinfestation.
How Fleas Overwinter
No flea stage can survive in near-freezing temperatures for extended periods. However, some fleas don’t get subjected to extreme cold. Adults can survive on warm-bodied hosts, such as dogs, cats and raccoons. Fleas can also live all year long if their host lives in a warmed shelter. For example, fleas will survive in heated homes, where, consequently, most domestic infestations occur. The freeze-protected dens of wild animals can keep immature fleas alive during winter as well.
Img 1 Raccoons are active in the winter and fleas can survive on their warm bodies.
Fleas don’t Hibernate
Fleas don’t have a true diapause stage. They don’t hibernate or go dormant to overwinter. Adults can enter a quiescent (inactive) state within their cocoon for up to 5 months, but temperatures below 37.4°F (3°C) kill them. Still, pre-emerged adults can survive winters in slightly warmed or insulated structures (e.g. crawl spaces), and then emerge in spring when conditions are better. It’s also possible for them to live through short, mild winters outdoors.
Cold Temperatures Kill Fleas
Adult fleas die in temperatures below freezing (Fig 2). Death occurs within five days at 30.2°F (-1°C). Within 24 hours, 20% of emerged adults and 72% of pre-emerged adults are killed in subfreezing temperatures. They’ll survive longer above freezing (37.4°F), but still ultimately die within 10 days.
Fig 2 Percent of emerged adult fleas that survive (y-axis) across 40 days (x-axis).
When temperatures rise above 46.4°F (8°C), nearly half of emerged adults stay alive for 20 days. However, immature stages can’t survive in these temperatures.
Flea eggs hatch in 12 days at 50.4°F (10°C), but the larvae will quickly die. At 46.4°F (8°C), nearly half of the eggs are killed in a day, 65% die by day five, and there’s a complete kill by day ten (Fig 3). At 37.4°F (3°C), 65% of the flea eggs die within a day. Survival isn’t possible below freezing.
Fig 3 Percent of eggs that survive (y-axis) across 10 days (x-axis).
The larval stage is most susceptible to cold conditions. The low-end extreme occurs at 55.4°F (13°C). Flea larvae die within 10 days of hatching at 50°F (10°C). Another study found similar results, where 59°F (15°C) was the low-end extreme. At 46.4°F (8°C), 65% of larvae die within 10 days and 100% die by day 20. At 37.4°F (3°C), 37% of the larvae die in a day and none live past day five.