Colias scudderi
In 3 days ~20% in a week ~50%
Colias scudderii, the willow sulphur, is a butterfly in the family Pieridae. It is found from Alaska south through the Rocky Mountains to northern New Mexico. The habitat consists of mountain meadows and willow bogs. The wingspan is 38–51 mm (1.5–2.0 in). Adults are on wing from June to August. They feed on flower nectar.
The larvae feed on the leaves of Salix species (including Salix reticulata, Salix lutea and Salix planifolia). Second, third, and fourth instar larvae hibernate. Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Rocky Mountain National Park | 🇺🇸 United States |
More parks will be added in future updates.
With luck
About 10% of wildlife watchers report a Colias scudderi sighting in Rocky Mountain National Park on a given day, based on 28 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 51st most-seen of the 191 insects we can rate there. Over three days the chance rises to about 20%, and over a week to about 50%, if each day is a fresh chance.
July and August
In those months about 10% of wildlife watchers report a Colias scudderi in Rocky Mountain National Park on a given day, against under 5% in September to June, the lowest months.
Between 11 am and 2 pm
Across all the parks we cover, that three-hour window holds the most Colias scudderi sightings with a recorded time, and nearly all of them come between 6 am and 6 pm: it is a daytime animal.
Only Rocky Mountain National Park, in our data
Rocky Mountain National Park is the only park on Wallace's Line with enough records to rate Colias scudderi sightings: about 10% of wildlife watchers there report one on a given day.
Same genus: Colias
The closest relatives of the Colias scudderi that you can see in Rocky Mountain National Park (genus Colias, Clouded Yellows) are Mead's Sulphur (about 10%), Queen Alexandra’s Sulphur (about 10%) and Clouded Sulphur (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Colias scudderi is recorded against all the insects logged in Rocky Mountain National Park (28 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.
