Why do fleas hop on a person? - briefly
Fleas leap onto humans because their hind legs contain a spring‑like protein called resilin that stores energy and releases it in a millisecond burst, enabling jumps several centimeters high to reach a host. They are drawn by body heat, carbon‑dioxide and movement, which activate the jumping response.
Why do fleas hop on a person? - in detail
Fleas locate a human host through a combination of heat, carbon‑dioxide, movement, and scent. Their sensory organs detect the temperature gradient of warm‑blooded bodies, the rise in CO₂ exhaled during respiration, and the vibrations generated by walking. These cues trigger a rapid pursuit response.
The flea’s jump is powered by a highly specialized resilin pad in its hind legs. Before leaping, the insect stores energy by compressing this elastic protein, then releases it in a fraction of a millisecond. The resulting acceleration can exceed 100 g, propelling the flea up to 150 mm vertically and 200 mm horizontally—distances many times its own body length. This mechanism enables the flea to bridge the air gap between the ground and a passing person.
Once airborne, the flea steers by adjusting the angle of its legs and abdomen, allowing it to aim for the nearest surface. Upon contact, its claws quickly grasp hair shafts or skin folds, and its mouthparts pierce the epidermis to begin feeding. The ability to jump rather than crawl reduces exposure to predators and environmental hazards, increasing the likelihood of successful host attachment.
Key factors that make humans attractive targets:
- Body heat creates a thermal signature detectable from several centimeters away.
- Exhaled CO₂ forms a plume that rises and spreads, guiding the flea upward.
- Sweat contains volatile compounds (e.g., lactic acid) that act as chemical attractants.
- Movement creates air currents that the flea can follow toward a potential host.
In summary, fleas combine acute sensory detection with a powerful, elastic‑driven jump to reach a human host efficiently. Their anatomical adaptations, environmental cues, and behavioral strategies together explain why they frequently land on people.