Bug FAQWestern Sulphur
Colias occidentalis · Order: Lepidoptera · Family: Pieridae
Also called: Golden Sulfur
The western sulphur is a large yellow butterfly with a single white spot on each hindwing surrounded by a red ring, and females sometimes appear in a rare white form called alba. Caterpillars feed on Vicia, Lupinus, Lathyrus and Thermopsis flowers, and adults fly once from late May to early July.
Source: Wikipedia
How to recognize it
The western sulphur is a large yellow butterfly with a single white spot on each hindwing surrounded by a red ring. Females sometimes occur in a rare white morph called alba.
Source: Wikipedia
Size
Its wingspan ranges from about 50 to 53 mm (2.0 to 2.1 in).
Source: Wikipedia
What it eats
The larvae feed on the flowers of Vicia, Lupinus, Lathyrus and Thermopsis species.
Source: Wikipedia
Life cycle
Adults have a single flight period from late May until early July.
Source: Wikipedia
When you see it
The one flight period occurs from late May through early July.
Source: Wikipedia
Where it is found in the US
Recorded in 9 of 51 states and DC. Most records: Washington, Oregon, California, Utah, Montana, Idaho, North Carolina, Wyoming.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Status: native in North America; native in Canada; native in United States. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
When can I see western sulphur butterflies?
Adults are on the wing from late May to early July.
Source: Wikipedia
What do western sulphur caterpillars eat?
The caterpillars feed on flowers of Vicia, Lupinus, Lathyrus and Thermopsis.
Source: Wikipedia
What does the western sulphur look like?
It is a large yellow butterfly with a single white spot on each hindwing surrounded by a red ring; females may appear in a rare white form called alba.
Source: Wikipedia
Same family (Pieridae)
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Colias_occidentalis
Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia
Text written 2026-10-24 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-24.