Fleas are attracted to heat, but it plays a relatively minor role in host-finding. A combination of multiple stimuli (e.g. light, heat, and movement) produce the best attraction response.
Cat fleas locate hosts chiefly through visual and thermal stimuli. A combination of multiple cues (light, movement, air currents, and heat) reinforces the likelihood of finding suitable host, and thus produces the best jump response.
Thermotaxis: Attraction to Heat
The term thermotaxis describes attraction or repulsion to heat. Cat fleas are positively thermotactic, meaning they’re stimulated and attracted by warmth. This response helps them locate blood meals, as potential hosts emit body heat. Fleas have antennae which function as sensory organs. The antennae can detect heat and other host stimuli.
When a heated object is placed near cat fleas, their activity dramatically increases. They’ll jump wildly in random directions.
Fleas will jump towards sources of heat, being most attracted to targets at 104°F (40°C) Fig 1. Still, they’re highly attracted to temperatures all the way up to 122°F (50°C), which shows that they don’t discriminate between hosts. They aren’t specifically attracted to their preferred host’s body temperature.
Fig 1 Percent of cat fleas (y-axis) that jumped towards a target heated to different temperatures (x-axis) as opposed to a target of 80.6°F (27°C).
Heat Plays a Minor Role in Host-Finding
Although fleas are attracted to warmth, it isn’t a primary attraction stimulus. Fleas won’t jump when heat is the sole signal. They’ll orient themselves towards the warm object and prepare to jump, but won’t actually jump unless additional stimuli are present. Flea traps employing heat as the only stimulus won’t attract fleas. Similarly, adding heat to a lighted flea trap doesn’t improve performance. Overall, thermal cues play a minor role in detecting a host.
Fleas stay on their host once it’s acquired. They’ll typically only abandon an animal if it’s dead or dying. Once the host’s body temperature begins dropping, the fleas jump off and onto the nearest warm animal. In natural settings, predators may acquire fleas after killing flea-infested prey.
Heat & Pre-emerged Adults
Heat is a crucial host cue for pre-emerged adults. Once fully developed, adult fleas remain inside their cocoons until they detect a host. They can remain in a quiescent state for up to 5 months. The two cues which trigger emergence are heat and physical pressure. Together, they indicate that a warm-blooded animal is resting on the cocoon. Warm human breath is enough to stimulate cocoon emergence. Vacuuming can simulate the cues that cause fleas to emerge.