Britain's butterflies are in severe decline. As potentially sentient invertebrates, their welfare matters both individually and as a measure of ecosystem health.
The welfare case for butterflies is built on a foundation of uncertainty but also genuine ethical obligation. Caterpillars show clear responses to noxious stimuli that suggest nociception, though whether this involves conscious suffering is unknown. At population level, the mass mortality caused by pesticide drift, habitat loss, and inappropriate land management represents a precautionary welfare concern on a vast scale. The most important welfare interventions are also the most important conservation interventions: restoring unimproved grasslands, reinstating traditional coppice woodland management, and reducing pesticide use on agricultural land.