Butterflies Go From the West

Butterfly numbers in the US, to the West of the Rocky mountains, have been declining by circa 1.6% per year since 1977 (https://www.theguardian.com/environment/2021/mar/04/butterfly-numbers-plummeting-us-west-climate-crisis). This staggering loss of butterflies in Western USA, appears largely down to human-mediated rises in temperature. Temperatures, of course, influence the plants on which the larvae and adults feed. No plants of particular species: no butterflies. Plant populations move slowly and can, of course, only colonise cooler northly locations (or mountain tops), until they run out of land. Butterfly species can move more quickly than plants but this might be the reason that their declines are so obvious. Other species might come in to take the places of the missing butterflies on new vegetation. At the current rate of decline, however, few of the original species will be found to the West of the Rockys, by the middle of this century. Migratory species, like the Monarch butterfly, are likely to be especially endangered by this process.