Aglais milberti
In 3 days ~20% in a week ~40%
Aglais milberti, the fire-rim tortoiseshell or Milbert's tortoiseshell, is considered the only species of the proposed Aglais genus that occurs in North America. It is one of two tortoiseshell butterflies in North America. The other species is the nymphata californica or California Tortoiseshell (California tortoiseshell).
The data is muddled on the range of the two recognized tortoiseshell species. Similar species distributions exist and have separate migration patterns for other butterflies with the same geographical ranges. Western monarchs, for example, migrate between southern BC, coastal CA and Pacific Mexico. Eastern monarchs can be found east of the Rockies in Canada and migrate along the Eastern American coast into interior Mexican highlands. The mountain ranges are often physical borders between distinct populations and migration. (Danaus plexippus)
The wingspan is between 4.2 and 6.3 cm and the forewing's tips are squared off. The upperside is black with wide orange submarginal bands; this orange slightly fades to yellow near the inner edge. Both wings have narrow black marginal borders; the hindwing may have blue spots.
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| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Wood Buffalo National Park | 🇨🇦 Canada | |
| 2 | Elk Island National Park | 🇨🇦 Canada | |
| 3 | Gros Morne National Park | 🇨🇦 Canada | |
| 4 | Riding Mountain National Park | 🇨🇦 Canada | |
| 5 | Banff National Park | 🇨🇦 Canada | |
| 6 | Glacier National Park | 🇺🇸 United States | |
| 7 | Jasper National Park | 🇨🇦 Canada | |
| 8 | Grand Teton National Park | 🇺🇸 United States | |
| 9 | Yellowstone National Park | 🇺🇸 United States | |
| 10 | Sequoia and Kings Canyon National Parks | 🇺🇸 United States | |
| 11 | Rocky Mountain National Park | 🇺🇸 United States | |
| 12 | Great Bear Rainforest | 🇨🇦 Canada | |
| 13 | Yosemite National Park | 🇺🇸 United States | |
| 14 | Olympic National Park | 🇺🇸 United States |
With luck
About 10% of wildlife watchers report a Milbert's Tortoiseshell sighting in Yosemite National Park on a given day, based on 26 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 75th most-seen of the 227 insects we can rate there. Over three days the chance rises to about 20%, and over a week to about 40%, if each day is a fresh chance.
June to October
In those months about 10% of wildlife watchers report a Milbert's Tortoiseshell in Yosemite National Park on a given day, against under 5% in November to May, the lowest months. Those are among Yosemite National Park's driest months, with about 30 mm of rain a month against 220 mm in January.
Between 11 am and 2 pm
Across all the parks we cover, that three-hour window holds the most Milbert's Tortoiseshell sightings with a recorded time, and nearly all of them come between 6 am and 6 pm: it is a daytime animal.
13th of 14
Of the 14 parks where we can rate Milbert's Tortoiseshell sightings, Yosemite National Park ranks 13th at about 10%. The best odds are in Wood Buffalo National Park (Canada, about 40%), Elk Island National Park (Canada, about 40%) and Gros Morne National Park (Canada, about 30%).
Same family: Nymphalidae
The closest relatives of the Milbert's Tortoiseshell that you can see in Yosemite National Park (family Nymphalidae, Brush-footed Butterflies) are Limenitis bredowii (about 40%), California Tortoiseshell (about 30%) and Mormon Fritillary (about 20%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Milbert's Tortoiseshell is recorded against all the insects logged in Yosemite National Park (26 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
