Cat fleas are more active at night than during the day. They can be loosely labeled as nocturnal. They can also be described as vespertine since their activity peaks at dusk. Still, fleas are never completely inactive, making their behavior difficult to categorize.
Circadian Rhythm of Fleas
Fig 1 Mean activity of cat fleas (y-axis) at every hour across a day (x-axis). The scotophase (dark cycle) occurred from 1000 to 2000 hours.
Fleas “wake up” a few hours before dusk. Their locomotive activity peaks at twilight, then gradually decreases throughout the night until reaching the lowest point at dawn. Fleas don’t move much throughout daylight hours Fig 1. Egg-laying occurs in similar patterns. Most eggs are laid in the middle of the night, and the fewest shortly after dawn.
Fleas are never completely inactive. Feces are excreted randomly or constantly throughout all hours of the day.
Nocturnal or Vespertine
It’s difficult to categorize cat flea behavior. They can be described as nocturnal, since they’re relatively inactive during daylight hours. However, their activity never completely ceases. Additionally, known studies were done in laboratory settings, not on animals. Fleas may be more active on hosts.
Cat flea behavior is also loosely crepuscular. Crepuscular animals are active at twilight—dusk or dawn. Narrowing this down, vespertine animals are exclusively active at dusk. The term implies that activity terminates at full darkness. While cat flea activity does peak at sunset, they remain active throughout the night. Thus, they don’t strictly fit this label either.