Saturday, May 16, 2015

Species Profile: Swallowtails

The butterfly season is in full swing; the Spring-fliers are wrapping up at the lower elevations and early Summer species are starting to appear.  Right now is the perfect time to see all six species of swallowtails on the wing in Washington and Oregon!  Indra and Anise swallowtails have finished flying in many locations but may still be seen at higher elevations, while the Oregon Swallowtail should be emerging soon, and the Western Tiger, Pale Tiger, and Two-tailed Tiger swallowtails are all on the wing in most locations.  I've previously written about Oregon Swallowtails here, and Anise and Indra swallowtails here.  Because swallowtails are fairly common and easily noticed by many people, I am frequently asked questions about them and how to tell them apart.
One misunderstanding that comes up, more often than some might think, is that these are Monarchs. Although a quick look at pictures of swallowtails (yellow and black) and Monarchs (orange and black) quickly clears up this issue, I think the reason some people are confused is because Monarchs are so often talked about in public forums (media, classrooms, etc.) and swallowtails are large, widespread and very common, so people assume they must be the oft-mentioned Monarch.  Although there are many things about the Monarch that make it special, I am often discouraged that it is held in such high regard while so many other equally or even more unique butterfly species are ignored.  Not taking away from the Monarch, just wishing that more interest was shown in other species.

Swallowtails in our area can be divided into two groups: "black" swallowtails and "tiger" swallowtails.  The first are generally known by their half black, half yellow wings, relatively short tails, and large red eyespot on the hindwing.  The second are known by their familiar black tiger stripes on mostly yellow (or white) wings and longer tails.  As larvae, black swallowtails primarily feed on plants in the parsley family, including desert parsley (Lomatium spp.) with the exception of the Oregon Swallowtail, which feeds only on tarragon (Artemisia dracunculus).  Tiger swallowtails primarily feed on broadleaf trees such as willow, birch, aspen, and chokecherry.  All swallowtails overwinter as a brown or green chrysalis.

Indra Swallowtails are mostly black and have the shortest tails of all these species.  They only use a few species of Lomatium, and are usually found on rocky slopes and canyons on the east side of the Cascades.
Black swallowtail group: Indra, Anise, and Oregon swallowtails.
Anise Swallowtails are common throughout Oregon and Washington.  They are deep yellow and the black pupil in the eyespot is completely surrounded by red.  Oregon Swallowtails are restricted to east-side locations where their host tarragon is found.  They are butter-yellow and the black pupil is bordered by yellow on the lower edge, or is sometimes much reduced (see below).
Comparison between Anise and Oregon swallowtails
Western Tiger Swallowtails are bright lemon yellow with wide black tiger stripes and a single tail.  Two-tailed Tiger Swallowtails are usually darker yellow (faded individuals may appear more similar to Western Tigers in color), have narrow tiger stripes, and a small second tail.  Female Two-tailed Tigers often have wider stripes and appear more like Western Tigers, but are generally larger and have the second tail.  Western Tigers are found throughout Washington and Oregon, while Two-tailed Tigers are only found from the crest of the Cascade range eastward, except in southern Oregon where they range out to the coast.  Pale Tiger Swallowtails are white or cream with wide black stripes and are found through most of western Washington and Oregon and most forested parts of the eastern side of the states.
Tiger swallowtail group: Western, Two-tailed, and Pale tiger swallowtails.

2 comments:

  1. Thank you for this. It helped ID a two-tailed tiger that we ran into in Bend today. It always amazes me what agile flyers swallowtails are.

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  2. Thank you Caitlin on your post regarding the diffs between P. zelicaon & P. machaon. I spotted what looked to be an old, beat up anise swallowtail, but it isn't listed as observed here in Yavapai County, Az. Your illustration and description of it as being "butter-yellow" leads me to believe I saw a P. machaon, which is observed and recorded here.

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