Milbert’s Tortoiseshell

Nymphalis milberti

Milbert’s Tortoiseshell is a swift flying butterfly that is always a pleasure to see. This butterfly like the Compton Tortoiseshell varies widely in abundance from year to year. There have been years where I haven’t seen even one Milbert’s Tortoiseshell, but 2005 was a banner year for this species. I saw more Milbert’s Tortoiseshells on one day, than I had seen previously in my whole life. During an NABA count in Buffalo County on July 15, 2005 we counted 136 of this species, but before we started counting, I had seen them in abundance along the roadsides on the way to the count site. It was reminiscent of the Red Admiral outbreak of 2001 where I did count over 400 along about a quarter mile stretch of back road. I am not sure about the reasons for them congregating on the road, but they only congregate like this in the early part of the day, and from 9:00-10:00 they disperse. Although we did see some still searching for minerals on the gravel roads, most were dispersed and many of the ones we counted were nectaring. There were still many caterpillars on nettles, and this species was common and flying well into October.

Identifying characteristics

Above, this species has a wide, dark brown margin on all four wings and a very bright orange, but fading to a more yellowish color towards the body, submarginal band. There is a row of blue spots in the hindwing margin, very similar to that in the Mourning Cloak. Below, the Milbert’s Tortoiseshell is a dark brown with a much lighter submarginal band.

Similar species

None in Wisconsin.

Habitat

Woodland edges and along streams and roadsides where its host plant nettles is found.

Flight

Two or more broods. Overwinters as an adult and may be found from early March through October.

Abundance

Varies in abundance from year to year. It can become quite abundant where counts of over 100 of this species are not uncommon. On the other hand, many years I am happy to see a single individual of this species on a butterflying trip.

Early Milbert's Tortoiseshell Sightings

Date	County	Reported by
Mar 11, 2006	Eau Claire	Aimee Beck
Mar 11, 2006	Eau Claire	Aimee Beck
Mar 11, 2006	Grant	Andy Paulios
Mar 22, 2006	Eau Claire	Dan & Mary Fisher
Mar 23, 2003	Dane	Jason Sailing

Locations