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Milbert’s Tortoiseshell (Aglais milberti)

The Milbert’s Tortoiseshell butterfly, scientifically known as Aglais milberti, stands as a unique specimen among North American butterflies. This species, which has sparked debate over its genus classification—fluctuating between Aglais and Nymphalis—showcases the vibrant diversity of the butterfly world. Its presence across various regions of North America, coupled with its distinctive appearance and behaviors, makes it a fascinating subject for both enthusiasts and researchers.

Milbert’s Tortoiseshell

Scientific Classification

  • Family: Nymphalidae
  • Genus: Aglais
  • Common names: Fire-rim tortoiseshell
  • Scientific Name: Aglais milberti


Aglais milberti is not just any butterfly; it is the only species of its genus found in North America, highlighting its exceptional status in the region’s fauna. The discussion regarding its classification reflects the complexities of entomological taxonomy and hints at the evolutionary intricacies of these winged beauties. The Milbert’s Tortoiseshell is particularly noted for its vivid colors, which set it apart from its counterparts, offering a glimpse into the rich tapestry of butterfly biodiversity.

Description and Identification


The larva of the Milbert’s Tortoiseshell is characterized by its dark, almost black body adorned with spiny projections. This intimidating appearance serves as a deterrent to predators, ensuring its survival through the vulnerable larval stage.


Transitioning into the pupa stage, the chrysalis adopts a brown hue accented with black outlines, a camouflage that blends seamlessly into its surroundings, providing protection from predators during this transformative period.

Adult Butterfly

Sexual Dimorphism: Sexual dimorphism is evident in this species, with variations in size, color intensity, and pattern details between males and females, allowing for easier identification of the sexes.

Color and Appearance: When their wings are spread open, the upper side reveals striking orange bands that fade into yellow towards the inner edges. Both the fore and hind wings are framed by black borders, with the latter occasionally adorned with small, blue spots. In contrast, the underside of the wings presents a more subdued appearance, with black dominating and a subtle brown band visible.

Milbert’s Tortoiseshell ButterflyAglais MilbertiAverage Wingspan: Adults of this species boast an average wingspan ranging from 4.2 cm to 6.3 cm (1.65 – 2.48 in), a size that facilitates their fast and agile flight patterns.

Flight Pattern: The flight of the Milbert’s Tortoiseshell is remarkably swift, an adaptation that serves well for evasion and efficient foraging across their habitats.


The eggs are laid in clusters, showcasing a round shape and a vibrant green color, which helps them blend into the foliage where they are placed.

Quick Facts

DistributionFound throughout the western and eastern United States, encompassing Alaska and Canada.
HabitatPrefers wet woodlands, moist marshes, and pastures for its rich feeding and breeding grounds.
Lifespan of AdultsApproximately 10 days, highlighting a brief but vibrant life cycle.
Host PlantsFavors lilac, thistles, and goldenrod for larval nourishment.
Adult DietEngages in feeding on a varied diet including nectar, dung, plant sap, and rotting fruit, showcasing its adaptability.

How to Identify Milbert’s Tortoiseshell?

Identifying the Milbert’s Tortoiseshell can be a rewarding experience for butterfly enthusiasts. Start by looking for the distinctive orange and yellow bands on the upper side of their wings when open, bordered by black with possible blue spots on the hind wings. Their fast and erratic flight pattern is also a key identifier. In their habitat, observe areas near wet woodlands, marshes, and pastures, where adults are likely to be found feeding on nectar, dung, plant sap, and rotting fruit. Note the sexual dimorphism in size and color intensity when trying to identify males from females. Spotting their unique eggs or caterpillars can also signal their presence in the area.

Did You Know?

  • The Milbert’s Tortoiseshell butterfly is divided into four subspecies: Aglais milberti milberti, Aglais milberti viola, Aglais milberti furcillata, and Aglais milberti pullum, each adapted to specific regions and conditions within North America.
  • Despite its brief adult lifespan of around 10 days, this butterfly engages in a remarkable journey of transformation and migration, contributing significantly to the pollination of various plant species.
  • This species’ adaptability in diet and habitat preferences makes it a resilient figure in its ecosystems, capable of thriving in a range of environmental conditions.


The Milbert’s Tortoiseshell butterfly encapsulates the beauty and complexity of North American butterflies. Its unique identification marks, vibrant life stages, and ecological significance make it a captivating subject of study and observation. Whether you’re an avid butterfly enthusiast or a curious observer, the Milbert’s Tortoiseshell offers a glimpse into the intricate world of these fascinating insects, reminding us of the diversity and resilience of nature.

Milbert’s Tortoiseshell Pictures

Fire-rim Tortoiseshell
Milbert’s Tortoiseshell Images
Milbert’s Tortoiseshell Pictures

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Scientific Classification

  • Family: Nymphalidae
  • Genus: Aglais
  • Common names: Fire-rim tortoiseshell
  • Scientific Name: Aglais milberti
Published by Avatar on August 2, 2019.
Last Updated: February 29, 2024. ✅ Verified by: Butterfly Team