California’s sage scrub habitats support a diversity of nectar and host plants for migrating and resident populations of painted lady butterflies (Vanessa cardui) throughout all seasons. The V. cardui North American migration is not an annual occurrence and is instead dependent on winter weather patterns at breeding grounds near the US–Mexico border. Thus, the irregularity of these migrations makes it difficult to study floral resource use along the migration route. Here we used the community science platform iNaturalist to quantify patterns in V. cardui nectar resource use in sage scrub over time and space during both migratory and non-migratory years. We identified over 329 different nectaring plant species of varying functional types (72% native to California) visited by adult V. cardui, 195 of which had not been previously identified as known nectar plants for V. cardui. Vanessa cardui butterflies were observed in similar locations regardless of whether a migration occurred, indicating the presence of resident painted lady populations across California. Moreover, migration years were positively correlated with warmer and wetter local conditions at observation locations. Our results provide new insights into patterns of floral resource use by North American V. cardui by harnessing the power of community science data and while highlighting the factors associated with its periodic North American migration.

Painted lady observations were downloaded from iNaturalist (iNaturalist.org) and plants identified from each observation. We also extracted date, time, and climate data for the location of each observation.

data are in the first tab of the xlsx file and the explanation of all columns are in the metadata tab.