Western Tiger Swallowtail
Papilio rutulus
Description 2 3/4-3 7/8" (70-98 mm). Above and below, lemon-yellow with black tiger-stripes across wings and black yellow-spotted margins. 1 or 2 orange spots and several blue spots near black tail on HW; blue continuous all around outer margin of HW below. Yellow spots along outer black margin of FW below run together into band; uppermost spot on border of HW above and below is yellow.
Similar Species Tiger Swallowtail usually has distinct separate yellow spots on margin of FW below; HW uppermost spot is normally orange. Two-tailed Tiger Swallowtail has narrower stripes, more tails. Pale Tiger Swallowtail is paler, with darker veins below.
Life Cycle Egg deep green, shiny, spherical. Caterpillar, to 2" (51 mm), deep to light green, swollen in front, accentuating large yellow eyespots with black and blue pupils.
Dark brown, woodlike chrysalis overwinters slung from a twig or tree trunk. Hosts more limited than those of eastern Tiger, include willows, poplars, and aspens (Salicaceae), several alders (Alnus) and sycamores (Platanaceae).
Flight February in S. California, May in Washington, normally June-July in mountain areas. Up to 3 broods in low altitudes and latitudes, 1 in cooler places with shorter seasons. Present most of summer.
Habitat Widespread, but normally near moisture - canyons, watersides, trails, roadsides, parks and gardens; sagelands and mesas with creeks.
Range British Columbia south to Baja California, east through Rockies to Black Hills, and High Plains of Colorado and New Mexico. Rare east of Rockies.
Discussion The Western Tiger may be the most conspicuous butterfly in the West. The eastern and western species essentially replace each other along a diagonal line, northwest to southeast, although there may be some slight hybridizing along the dividing line. Such east-west species-pairs are not unusual among butterflies. In Western canyons, males of several species of swallowtails gather in spectacular numbers around mud puddles or beside streams, with the Western Tiger usually predominating.
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