Why do fleas jump on some but not others? - briefly
Fleas are attracted to specific sensory cues—heat, carbon dioxide, and vibrations—produced by viable hosts. Hosts that lack these signals or have incompatible fur or skin characteristics are ignored.
Why do fleas jump on some but not others? - in detail
Fleas are capable of powerful leaps because they store elastic energy in a protein called resilin, located in the pleural arch of their hind legs. When the muscle contracts, the arch bends, compressing the resilin. Release of this tension propels the insect upward, achieving accelerations up to 100 g. The magnitude of each jump depends on the insect’s size, age, and nutritional status; well‑fed adults generate larger forces than starving or immature individuals.
Host selection is mediated by a combination of sensory inputs. Thermal receptors detect the warmth of a potential host, while mechanoreceptors sense vibrations caused by movement. Chemical cues, especially carbon dioxide and specific skin odorants such as fatty acids and volatile amines, attract fleas. When these signals reach threshold levels, the nervous system triggers the motor pattern that initiates jumping.
Not all animals present the same suite of cues. Species that emit lower concentrations of CO₂ or have skin chemistry less attractive to fleas are less likely to be targeted. Additionally, fur density influences the ability of fleas to locate a suitable attachment point; dense, oily coats can hinder detection and reduce successful jumps.
Environmental conditions also affect jumping frequency. Low humidity desiccates the resilin protein, reducing its elasticity and consequently limiting jump performance. Ambient temperature influences muscle contraction speed; cooler temperatures slow the motor response, leading to fewer jumps.
Genetic variation among flea populations produces differences in sensory receptor expression and resilin composition. Strains adapted to specific hosts often exhibit heightened sensitivity to that host’s odor profile, resulting in preferential jumping behavior toward those animals.
In summary, flea jumping is governed by:
- Elastic energy storage in resilin (mechanical basis)
- Sensory integration of heat, vibration, CO₂, and skin odors (trigger mechanism)
- Host-specific chemical signatures and fur characteristics (target selection)
- Ambient humidity and temperature (environmental modulation)
- Genetic adaptations influencing receptor sensitivity and protein elasticity (population-level variation)
These factors collectively determine why fleas leap onto certain animals while ignoring others.