Bug FAQRusty Pyrausta
Pyrausta semirubralis · Order: Lepidoptera · Family: Crambidae
The forewings measure about 9 to 11 mm long and are dark brown on the base half, turning dull brick-red toward the tip, while the hindwings are a faded brick red. Adults fly from April through September, with numbers peaking in May. It lives along coasts and can be found inland up to roughly 9 000 ft, ranging from southern British Columbia down through California, Nevada, Colorado and Arizona.
Source: Wikipedia
Size
Forewing length ranges from 9 to 11 mm.
Source: Wikipedia
Where it lives
It inhabits coastal areas and can be found inland up to about 9 000 ft elevation.
Source: Wikipedia
Life cycle
The species was first described by Alpheus Spring Packard in 1873.
Source: Wikipedia
When you see it
Adults are on the wing from April through September, with a peak in May.
Source: Wikipedia
Where it is found in the US
Recorded in 9 of 51 states and DC. Most records: California, Oregon, Idaho, Washington, Colorado, Arizona, Montana, Nevada.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
When can I see adult Pyrausta semirubralis?
Adults are active from April to September, most abundant in May.
Source: Wikipedia
Where does this moth live?
It lives in coastal habitats and can be found inland up to about 9 000 ft, from southern British Columbia through California, Nevada, Colorado and Arizona.
Source: Wikipedia
Same family (Crambidae)
Box Tree MothCydalima perspectalisDamages trees, gardens or crops
Celery Leaftier MothUdea rubigalis
Elegant Grass-veneerMicrocrambus elegans
Hawaiian Beet Webworm MothSpoladea recurvalisDamages trees, gardens or crops
Garden Grass-veneerChrysoteuchia culmellaDamages trees, gardens or crops
Bluegrass Webworm MothParapediasia teterrellusDamages trees, gardens or cropsSources
- Wikipedia: https://en.wikipedia.org/wiki/Pyrausta_semirubralis
Look it up elsewhere: GBIF · iNaturalist · BugGuide · Wikipedia
Text written 2026-10-25 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-25.