Signal

"Signal" - what is it, definition of the term

A signal is a quantifiable alteration in a physical, electrical, or biological system that transmits information from a sender to a receiver, enabling detection, interpretation, or response; in entomology, for example, the rhythmic movement of a tick, the pheromone release of a bug, the tactile cue generated by a louse, and the vibrational pattern produced by a flea each constitute distinct signals that facilitate intra‑species communication and host‑seeking behavior.

Detailed information

In arthropods such as ticks, insects, lice, and fleas, chemical and mechanical cues serve as primary means of communication and environmental assessment. These cues originate from specialized glands, sensory organs, or external stimuli and are transmitted to conspecifics or potential hosts.

Chemical cues are released as volatile compounds or surface-bound substances. Ticks emit attractant molecules that guide them toward host skin temperature and carbon‑dioxide gradients. Fleas detect host pheromones and sweat constituents, triggering host‑seeking behavior. Lice rely on cuticular hydrocarbons to recognize members of the same species and to maintain colony cohesion. In many bugs, alarm pheromones are discharged when threatened, prompting rapid dispersal.

Mechanical cues involve vibrations and tactile signals. Ticks sense substrate vibrations caused by the movement of nearby organisms, allowing them to position themselves for attachment. Fleas respond to minute air currents generated by host locomotion, adjusting their jump trajectories accordingly. Certain bugs generate stridulatory sounds by rubbing body parts together; these sounds convey territorial or mating information. Lice use antennal tapping to assess the proximity of other individuals.

Signal reception is mediated by receptors tuned to specific frequencies or molecular structures. Sensilla on the tarsus of ticks detect temperature changes as small as 0.1 °C, enabling precise host localization. Flea antennae contain chemoreceptors that differentiate between host species based on odor profiles. Lice possess sensilla on the head that discern variations in cuticular hydrocarbon composition, facilitating species recognition.

The integration of multiple cue types enhances survival. For example, a tick may combine chemical attraction to carbon‑dioxide with vibration detection to confirm host presence before initiating attachment. Fleas synchronize odor detection with vibration sensing to optimize jumping timing, reducing missed opportunities. This multimodal processing allows these ectoparasites to adapt to variable environments and to efficiently locate hosts or mates.