What environmental factor can contribute to the growth of flea populations?

Flea populations thrive in warm and humid conditions, which create an ideal environment for them to reproduce and develop. Fleas prefer temperatures between 65°F and 80°F (18°C to 27°C) and require humidity levels of about 70% to 80% for optimal egg hatching and larval development. Under these conditions, the life cycle of fleas accelerates, leading to a rapid increase in their population. In contrast, low humidity levels and cold temperatures can significantly hinder their growth and survival, as these conditions are less favorable for their life cycle progression. Regular vacuuming can help control flea populations by removing adults, larvae, and eggs from the environment, making it an ineffective choice for fostering flea growth. Thus, the combination of warmth and humidity directly supports the growth and proliferation of fleas, making it the correct answer.