Hyalophora euryalus

Distinguished from other Hyalophora species by geographic range (western North America vs. eastern/central for H. cecropia and H. gloveri). H. euryalus occurs in drier intermontane habitats compared to the more mesic-forest associated H. cecropia. Adults active earlier in the year (January–July) than H. cecropia (spring–early summer in most of range). Wing pattern and coloration variable but generally with more extensive reddish tones than H. gloveri. Larval host plant association with Ceanothus is characteristic but not exclusive.

Dry intermontane valleys and interior regions. Associated with montane and foothill habitats where host plants occur. Found in areas with sufficient moisture to support host vegetation, including riparian corridors and mesic slopes within otherwise dry regions.

Western North America from interior British Columbia (north to Prince George along Fraser River) south through Washington, Oregon, California to Baja California, Mexico. Absent from coastal Pacific Northwest and most of the Great Basin desert proper.

Adults on wing from January to July depending on location, with earlier emergence at lower elevations and southern latitudes. Single generation per year (univoltine). Overwinters as pupa within cocoon.

Larvae feed on leaves of Ceanothus (Rhamnaceae), Rhamnus californica (Rhamnaceae), Prunus emarginata (Rosaceae), Arctostaphylos (Ericaceae), Alnus (Betulaceae), Betula (Betulaceae), Corylus (Betulaceae), Ribes (Grossulariaceae), Pseudotsuga menziesii (Pinaceae), Arbutus menziesii (Ericaceae), Liquidambar (Altingiaceae), and Salix (Salicaceae). Adults do not feed.

• Ceanothus - larval hostPrimary namesake host
• Rhamnus californica - larval host
• Prunus emarginata - larval host
• Arctostaphylos - larval host
• Alnus - larval host
• Betula - larval host
• Corylus - larval host
• Ribes - larval host
• Pseudotsuga menziesii - larval host
• Arbutus menziesii - larval host
• Liquidambar - larval host
• Salix - larval host

Complete metamorphosis with four stages: egg, larva, pupa, adult. Eggs deposited in clusters on leaves of host plants. Larvae progress through five instars, feeding gregariously in early instars, becoming solitary in later instars. Pupation occurs within a silken cocoon attached to vegetation, often with incorporated leaf fragments. Adults emerge following winter diapause, with timing dependent on temperature accumulation. Single generation per year throughout range.

Adults are nocturnal and strongly attracted to light. Males detect female sex pheromones using their large, feathery antennae. Larvae may exhibit gregarious feeding in early instars, dispersing as they develop. Defensive behaviors include thrashing and use of urticating setae.

Larvae function as generalist herbivores, consuming foliage of diverse woody plants. Adults serve as prey for birds, bats, and other insectivores. Pupae in cocoons may be consumed by small mammals and birds. The species contributes to nutrient cycling through herbivory and serves as a food source in food webs.

Subject of ecological study due to sensitivity to introduced parasitoids. Potential impact from Compsilura concinnata, a tachinid fly introduced for gypsy moth biocontrol, has been documented to parasitize related Hyalophora species. No direct economic importance; not a pest species. Occasionally encountered by naturalists and moth enthusiasts.

• Hyalophora cecropiaSimilar large size and general morphology, but restricted to eastern and central North America; differs in habitat preference (more mesic forests) and typical adult activity period
• Hyalophora gloveriOverlaps in western range; distinguished by habitat, phenology, and subtle differences in wing pattern and coloration
• Antheraea polyphemusSimilar large saturniid with eyespots, but distinguished by translucent eyespots on hindwings and different geographic range

• saturniid
• giant silk moth
• western North America
• Ceanothus
• urticating hairs
• univoltine
• nocturnal
• light-attracted
• non-feeding adult

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
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