In homes, flea larvae live for 7-11 days before pupating. In ideal environments, they can fully develop in 4-7 days. In poor conditions, it may take 28-45 days for flea larvae to mature. How quickly they develop depends upon ambient temperature, relative humidity, and food availability.
Larval Growth Rates
In Ideal Conditions
Ideal flea larvae environments are warm, humid, and contains plenty of food. Under these conditions, the larvae can fully mature in as little as five days Fig 1.
Fig 1 Days it takes (y-axis) for 50% of flea larvae to form cocoons at different ambient temperatures (x-axis) while relative humidity is held constant at 75%.
In Poor Conditions
In unfavorable conditions, flea larvae may live for 28 to 45 days before pupating. Prolonged development occurs due to low humidity, cool temperatures, oxygen tension, and food shortages.
Temperature, Humidity & Food
The two primary factors governing how quickly larvae develop are relative humidity (RH) and ambient temperature. However, surrounding conditions are somewhat irrelevant, because flea larvae live in protected microhabitats. These areas have their own sheltered microclimates, where humidity is maintained and temperature is moderated.
Fig 2 Environmental conditions required for flea larvae to survive, and days it takes the larvae to fully develop from egg to cocoon.
A relative humidity of 75-92% is optimal for immature fleas. Larvae begin forming cocoons in 5 days at 90% RH, while taking twice as long at 50% RH. In a similar study, larvae raised at 65-85% RH took 4-5 days to develop, while taking 12 days at 50% RH.
The ideal RH occurs above 80%. Only 30% of larvae survive at 70% RH, while over 60% reach adulthood at 80-90% RH. Additionally, larvae are able to actively uptake water from the air when RH exceeds 75%. The larvae exposed to a higher RH develop into larger, healthier adults.
The optimal temperature for flea larvae occurs between 80.6°F and 89.6°F (27°C and 32°C). 88% of larvae survive at these temperatures and 75% RH. Many complete development within five days. Other studies corroborate this data. In one, the ideal temperature occurred between 77°F and 86°F (25°C and 30°C). In another, 99% of larvae survived at 90°F (32.2°C) and 80% RH. Some reached maturity in as little as four days.
Time to maturity progressively increases as temperature is lowered. At 69.8°F (21°C), 50% of larvae mature within 12 days. At 55.4°F (13°C), larvae don’t form cocoons until day 28. A different study found complete development took 45 days at 59°F (15°C).
Food shortages can result in insufficient nutrition and nearly double the time it takes larvae to develop. Additionally, malnourished larvae become slightly smaller adults.
Desiccation & Death
Of all life stages, larvae are most susceptible to death from desiccation. This makes them very sensitive to humidity. Extremes occur at 50% and 95% RH.
All flea larvae will desiccate when exposed to a RH below 50%, regardless of temperature. One experiment saw a slightly higher low-end extreme, with a RH of 60% being lethal. However, a different study showed that at 50%, 55%, and 65% RH, larval survival was 24%, 77% and 91%, respectively Fig 3.
Fig 3 Percent of flea larvae that survive (y-axis) at different increments of relative humidity (x-axis) while ambient temperature is held constant at 90°F.
At the other extreme, no larvae can survive at 95-100% RH, because of fungal growth on their substrate and food.
Flea larvae can only survive at temperatures between 55.4°F and 95°F (13°C and 35°C).
Larvae die at any temperature below 55.4°F (13°C). Similarly, one study found the low-end temperature occurred at 59°F (15°C). At 50°F (10°C), flea larvae die within 10 days of hatching from eggs. At 46.4°F (8°C) and 75% RH, 65% of larvae die within 10 days, and all perish by day 20. At 37.4°F (3°C), 37% die within a day, and 100% die within five days.
Temperatures above 95°F (35°C) are lethal to flea larvae. Only 30% live long enough to form cocoons, and they’ll never emerge to complete their development into adults. Outdoors, when temperatures exceed 95°F (35°C) for more than 40 hours a month, there’s complete mortality in flea larvae.
Fig 4 Percent of flea larvae that survive (y-axis) throughout different increments of relative humidity (x-axis), at three constant ambient temperatures.
Unfed cat flea larvae will die from starvation within three days if they’re unable to find food.