Flea season is typically most active during the warmer months of the year, starting in early spring and continuing through summer and into fall. The ideal temperature range for fleas is about 75° to 85° Fahrenheit with high humidity, around 90%. Fleas thrive in warm and humid conditions, so flea season can last anywhere from about 6 to 9 months, or even year-round in warmer climates. In many parts of the United States, flea season starts as early as February to March and can last through September, October, or even November. In warmer states such as California, Texas, Florida, and other southern or coastal states, fleas can be active all year round due to mild winters and favorable conditions. To summarize:

• Fleas become active with rising temperatures in early spring.
• Peak flea activity is usually during spring, summer, and early fall.
• Flea season varies by location, lasting 6-9 months or year-round in warm climates.
• Fleas can be a threat indoors even in colder months because of indoor heating.
• Flea season generally ends when temperatures consistently drop below 45°F.

This means flea season roughly spans from early spring through fall, but in warmer regions, it can persist year-round.