Fleas don’t sleep. However, they do have cycles of rest and activity. Fleas are most active around sunset, and least active at sunrise. At dusk, there’s an increase in movement, egg production, and respiration. Fleas are never completely inactive. They produce eggs and feces through all hours of the day.
Cocooned adult fleas can enter into a quiescent (dormant-like) state for up to 5 months. However, cat fleas don’t have a true diapause or overwintering stage.
Do Insects Sleep?
Insects don’t sleep in the same way as mammals. However, they do have circadian cycles of rest and activity. During the rest cycle, they won’t respond much to surrounding stimuli. Their sensory systems become somewhat insensitive, which is similar to sleep in other animals.
Fleas are most active as the day transitions into night. Keep in mind, the following studies were done on unfed fleas in a laboratory setting. Activity on hosts hasn’t been studied.
Time of Day
Cat fleas are most active in the evening, and least active in the morning. A peak in locomotive activity occurs a few hours before dusk Fig 1. Activity then gradually decreases throughout the scotophase (dark cycle), reaching the lowest point at dawn. Fleas remain largely inactive throughout most of the photophase (light cycle).
Fig 1 Mean locomotor activity of cat fleas (y-axis) at every hour across a day (x-axis). The scotophase (dark cycle) occurred from 1000 to 2000 hours.
Light & Dark
The effects of light and dark cycles was tested on flea locomotion. In a 24 hour (12:12, L:D) period, flea activity began increasing a few hours before the scotoperiod, peaking at the light/dark transition period. Activity declined over night, reaching the lowest point at the beginning of the photophase. When the lights went on, activity slowly began to increase again.
In the same study, the light and dark cycles were swapped (lights on at night). Similar activity patterns were observed, with more movement in the dark. However, the activity peak occurred a little later on in the scotophase.
When studying the efficacy of flea traps, more fleas were caught at night than in daylight hours. This provides further evidence that fleas are more active in the dark.
Egg production is affected by the time of day. Oviposition rates begin to increase shortly after sunset, peaking in the middle of the scotophase Fig 2. The number of flea eggs laid then declines until it reaches the lowest point shortly after sunrise. Generally, egg production is higher at night, which coincides with the sleep patterns of domestic pets.
Fig 2 Number of eggs produced per cat flea (y-axis) at every hour across a day (x-axis). The scotophase (dark cycle) occurred from 1800 to 0600 hours.
One study observed egg production at three time periods spanning a day. 87.7 eggs were laid during the last 8 hours of the scotophase. 49.9 eggs were deposited during the 8 hours of light. And the 8 hour transition period from light (2 hours) to dark (6 hours), accounted for 59.1 eggs. While more eggs were laid in the dark, no correlation was found between egg production and pet sleeping patterns.
Time of day has no significant impact on fleas’ rate of fecal excretion. Feces is produced at a random or constant rate throughout the day Fig 3.
Fig 3 Amount of feces in mg excreted per cat flea (y-axis) at every hour across a day (x-axis). The scotophase (dark cycle) occurred from 1800 to 0600 hours.
The effect of circadian rhythm on cat flea respiration was also studied. CO2 levels were measured in tubes with fleas. Some tubes were kept in the dark, and some in the light. Fleas kept in the dark produced less CO2. However, the most important factor was time of day. Flea respiration peaked at 18:00 Fig 4. This correlates with when they’re most active, in the evening before shortly before dusk.
Fig 4 Relative CO2 levels in tubes with cat fleas (y-axis) every 4 hours throughout a day (x-axis).
Dormancy & Diapause
Cocooned adults can enter into a sleep-like state. After pupating, fully developed adults can stay in their cocoons for extended periods of time. The quiescent period can last for up to 5 months. However, the fleas rapidly awaken and emerge upon detecting warmth and pressure. These cues indicate that a host is near.
After emerging from cocoons, cat fleas can’t enter into a dormant state. They don’t have a true diapause stage where they hibernate or overwinter.