All of a sudden (this past week) there are Dainty Sulphur butterflies (Nathalis iole) all over the west part of San Diego county, after not being seen much prior. Does this constitute an irruption? I’m not sure about the appropriate usage of the term.
Also does anyone have knowledge or a theory on why there are so many right now, this year, this week, etc. I had never seen one before, and have seen about 40 in the last week across multiple locations.