How do lice smell? - briefly
Lice do not possess a true olfactory system; they sense chemical cues via specialized sensory hairs rather than conventional smelling. Their chemosensory receptors detect volatile substances on the host’s skin and hair.
How do lice smell? - in detail
Lice locate hosts primarily through chemical cues detected by specialized sensory structures. The antennae and maxillary palps contain numerous sensilla equipped with olfactory receptor neurons that respond to volatile compounds emitted by humans. Electrophysiological recordings show activation by carbon dioxide, lactic acid, and a suite of skin‑derived volatiles. Behavioral assays confirm attraction to these substances at concentrations comparable to those found on the scalp or body surface.
Key odorants identified in laboratory studies include:
- Carbon dioxide (CO₂) – universal respiratory by‑product, triggers up‑wind movement.
- Lactic acid – abundant in sweat, elicits strong chemotactic response.
- 1‑Octen‑3‑ol – fungal‑derived volatile, detected by many hematophagous insects, contributes to host finding.
- Indole and skatole – products of bacterial metabolism on skin, enhance attraction.
- Fatty acids (e.g., hexanoic, octanoic) – components of sebum, guide lice to hair shafts.
Species‑specific differences exist. Head lice (Pediculus humanus capitis) show heightened sensitivity to scalp‑derived volatiles, while body lice (Pediculus humanus humanus) respond more robustly to clothing‑associated odors such as ammonia and urea. Pubic lice (Pthirus pubis) exhibit a narrower olfactory range, relying heavily on close‑contact cues.
The olfactory system operates with a limited receptor repertoire. Genomic analyses reveal fewer odorant‑binding proteins than in mosquito species, suggesting reliance on a combination of chemical, thermal, and tactile signals. Temperature gradients and vibrational cues complement odor detection, ensuring precise host localization.
Research methods combine gas chromatography–mass spectrometry (GC‑MS) to profile human skin volatiles with single‑sensillum recordings that map neuronal responses. Quantitative thresholds indicate detection of CO₂ at ~0.5 % and lactic acid at micromolar concentrations, levels readily present on a living host.
In summary, lice detect hosts through a constrained set of volatile chemicals, primarily CO₂ and sweat components, processed by antennal sensilla. This chemosensory strategy, augmented by heat and tactile information, enables efficient movement toward a suitable feeding environment.