For the past few weeks we have been witnessing the migration of thousands of southward-bound orange butterflies, a vast majority of which are not Monarchs (although they are having a good year, too) but Painted Ladies (Vanessa cardui). Both their large numbers and the length of time that they have lingered in the Northeast this fall are unusual.
This was a good year for Painted Ladies — they migrated north earlier than usual, arriving in mid-April, possibly giving them time to have an extra generation, reproducing twice instead of once during the summer. In addition, the unusual weather we’ve been having has not been great for migrating. The butterflies have spent a lot of time fueling up on nectar while waiting for a wind out of the Northeast to assist them in their flight to the Southwest. With the prevailing wind change we’re now experiencing, it’s likely many of them will resume their migration today.