This past weekend I stepped into my garden to be greeted by several red admiral (Vanessa atalanta) butterflies. According to our phenology records, the first sightings were in early April, but this year we started receiving reports of larger groups (rabbles) of admirals in late April. This is unusual for this species, which is territorial and usually found singly. It may be that warm southern winds helped to push the butterflies north.
Red admirals can only survive mild winter temperatures, so it is most likely that the butterflies we see in April are migrating from farther south. According to WI butterflies there are occasional outbreaks of large numbers of red admirals.in late June and early July. The last event was in 2007. It is not known what causes these outbreaks, but we do know they are the offspring of those early migrants who laid their eggs on nettles in early May. A friend who found herself in an outbreak a few years ago at Point au Sable said there were so many that she could hear them flyinng. Perhaps this year we might be privileged to see hundreds of these beautiful butterflies this summer. They are common through northeastern Wisconsin; look for them in woodland openings and suburban areas. And let us know at our phenology pages.
You can follow the migration on University of Iowa’s <em>Vanessa Migration website. Entomologist Royce J. Bitzer has been tracking the migration of these and other butterflies since 2001. You can enter your data and follow the North American migration in google maps.