Why do fleas bite only at night? - briefly
Fleas are chiefly nocturnal parasites, becoming active after dark when host movement is slower and visual detection is limited, which facilitates discreet blood‑feeding. Their nighttime activity also coincides with cooler temperatures and stronger carbon‑dioxide cues, improving host location.
Why do fleas bite only at night? - in detail
Fleas exhibit a feeding pattern that peaks after dark because several physiological and environmental cues align during this period.
During nighttime, host mammals are typically at rest, reducing the likelihood of grooming that would dislodge the insects. Immobility also creates a stable source of heat and carbon‑dioxide, both of which attract fleas. Their sensory organs—chemoreceptors for CO₂ and thermoreceptors for body heat—are more effective when the host’s body temperature remains constant and the surrounding air is cooler, a condition common after sunset.
Fleas are negatively phototactic; they move away from bright light. Low light levels suppress their activity in open spaces and drive them toward concealed microhabitats on the host’s fur, where they can locate a feeding site without exposure.
Additional factors that reinforce nocturnal feeding include:
- Humidity rise after dusk, which prevents desiccation of the flea’s exoskeleton.
- Reduced competition from other hematophagous insects that are active during daylight.
- Circadian rhythms encoded in the flea’s neural circuitry, synchronizing feeding bursts with the host’s sleep cycle.
Although fleas can bite at any time if conditions are favorable, the convergence of host inactivity, optimal sensory cues, and protective darkness makes the night the most advantageous window for blood acquisition. This timing maximizes the parasite’s survival and reproductive success.