Friday, October 4, 2013

Species profile: Oregon Swallowtail

Today I received an email from someone I've been in contact with who is establishing a butterfly garden in Maupin, Oregon, and it inspired me to write this article.  One goal of the garden was to attract Oregon Swallowtails, the official state insect, and to that end they have planted wild tarragon and several wildflowers in the garden.  It was only established this spring, but already they have found one full-grown caterpillar on the tarragon!  Although Oregon Swallowtail larvae are nearly impossible to distinguish from Anise Swallowtail (Papilio zelicaon) larvae, Anise Swallowtails tend to use desert parsley (Lomatium spp.) and other plants in the parsley family, while Oregon Swallowtails are exclusively found on wild tarragon (Artemesia dracunculus).  Also, the black and yellow stripe around each segment of the caterpillar is usually narrower on Oregon and wider on Anise swallowtails.  I have partially reared both species from late-instar larvae, and photos of those and other adults are pictured below.  Two years ago I wrote a profile for the Indra Swallowtail, another similar species, click here to see that article.

Oregon Swallowtail (Papilio machaon oregonius)
Wingspan: 2 1/2 to 3 inches
Male: Bright lemon yellow with black veins and wide black wing margins dotted with yellow. HW margin is dusted with blue scales. Slight orange blush above blue markings along VHW postmedian. Red eyespot capped with blue on HW near tail, black pupil on lower edge often appears as a short line or club, never centered in red spot. Abdomen is yellow with narrow black stripes along the length of the body.
Female: same.
Egg: pale yellowish-green; brownish blotches appear as it matures.
Larva: 1st, 2nd and 3rd instars are black with white and yellow markings giving them the appearance of a bird dropping. Final two instars are green, with alternating spots of yellow and black form bands around each body segment.
Pupa: pale green or brown.
Similar Species
Anise Swallowtail (P. zelicaon) has black abdomen with yellow side stripes, HW eyespot has centered black pupil. Indra Swallowtail (P. indra) is more black and has very short tails.
Habitat & Biology
Habitat: dry hills and meadows where its host plant is found. Adults often hilltop.
Overwintering stage: pupa.
Larval host: wild tarragon (Artemisia dracunculus).
Adult food source: numerous flowers such as daisies, asters, rabbitbrush, penstemon, milkweed, and dogbane. Males frequently visit mud.

Caterpillar and chrysalis of the Oregon Swallowtail (pupa darkened to brown within a day)
Newly-emerged Oregon Swallowtail (from the caterpillar above)
Oregon Swallowtail pumping up its wings
Oregon Swallowtail with empty chrysalis
Oregon Swallowtail (on the trailing edge of the hindwing, notice how the black spot seems to "melt" into the edge of the wing and is about halfway between the red and yellow, compared to Anise & Indra swallowtails that have a black spot completely surrounded by red and not touching the wing edge - see last two photos below)
Oregon Swallowtail males sipping from mud at Connors Lake boat launch, Sinlahekin Wildlife Area, Okanogan Co., WA

Anise Swallowtail on wet concrete, Deschutes River near Maupin, OR
Indra Swallowtail on wet sand, Deschutes River near Maupin, OR

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