Why do mice fear wormwood? - briefly
Rodents avoid wormwood because its leaves contain high concentrations of bitter terpenoids such as thujone, which are toxic and irritate their sensory receptors. This chemical deterrent triggers an innate aversion that reduces the likelihood of ingestion.
Why do mice fear wormwood? - in detail
Mice exhibit a strong aversion to wormwood (Artemisia spp.) because the plant contains bitter sesquiterpene lactones and aromatic terpenes that activate sensory receptors linked to danger detection. These compounds trigger the trigeminal nerve, producing a sharp, unpleasant sensation that discourages ingestion. The bitter taste also stimulates gustatory receptors that signal toxicity, prompting immediate avoidance.
Physiological mechanisms underlying the avoidance include:
- Activation of bitter‑taste receptors (T2Rs) on the tongue, which generate neural signals interpreted as harmful.
- Stimulation of olfactory receptors by volatile oils such as thujone, producing a repellent odor detectable at low concentrations.
- Induction of gastrointestinal distress when small amounts are ingested, reinforcing learned avoidance.
Ecological factors reinforce the behavior. Wormwood grows in habitats where rodents encounter it while foraging for seeds and grasses. Predators often exploit the same plant’s scent to mask their presence; mice that ignore the warning cues increase exposure to predation. Over evolutionary time, individuals displaying heightened sensitivity to wormwood compounds achieved higher survival rates, leading to the fixation of avoidance traits in populations.
Experimental observations support these conclusions. Laboratory tests show that mice will forgo food laced with wormwood extracts even when alternative options are scarce. Electro‑olfactogram recordings demonstrate robust neuronal responses to thujone concentrations as low as 10 ppm, confirming the potency of the odor cue.
In summary, the aversion results from a combination of bitter‑taste detection, repellent odor perception, and negative physiological feedback, all of which have been reinforced by natural selection to reduce the risk of toxin ingestion and predation.