What can fleas not do? - briefly
Fleas are incapable of flight because they have no wings and cannot sustain airborne movement. They also cannot survive more than a few days without consuming blood.
What can fleas not do? - in detail
Fleas are wingless insects, so they are incapable of flight. Their anatomy provides only a pair of hind legs specialized for jumping; no muscles or structures exist to generate lift.
Vision in fleas is reduced to simple eye spots that detect changes in light intensity. They cannot form detailed images, recognize colors, or track objects at a distance. Consequently, visual cues play no role in host detection.
Auditory perception is absent. Fleas lack tympanal organs or other structures that respond to airborne sound waves; they respond only to substrate vibrations transmitted through the host’s body.
Thermoregulation is non‑existent. As poikilothermic organisms, fleas cannot maintain internal temperature and become inactive or die when ambient temperature falls below roughly 10 °C (50 °F) for extended periods.
Water tolerance is minimal. Their exoskeleton does not repel moisture, and they drown when fully submerged. They cannot survive prolonged exposure to wet environments.
Nutritional intake is restricted to blood. Their mouthparts are adapted solely for piercing skin and sucking fluid; they cannot ingest solid food, digest plant material, or process non‑blood substances.
Reproduction requires a blood meal. Female fleas are unable to produce viable eggs without first ingesting host blood; in the absence of a host, egg production halts entirely.
Longevity without a host is limited. Adult fleas survive only a few weeks without blood, and larvae cannot develop to adulthood without the presence of a host‑derived protein source.
Mobility is confined to jumping and short crawling. Fleas cannot climb smooth vertical surfaces unaided; they rely on host contact for vertical movement.
These physiological and behavioral constraints define the capabilities fleas lack.