Kısaca
The moment they land on a flower, sensors in their feet analyze nectar quality and sugar content.
Butterflies taste with chemoreceptors in their feet. The moment they land, they detect sugar concentration, minerals, and toxic substances.
For female butterflies this is vital: they choose plants for their eggs by "tasting" with their feet. Wrong plant means death for caterpillars.
Their taste sensitivity is 200 times greater than humans.
Source: Journal of Insect Physiology