.

Two-tailed. Each hind wing has two distinct tails (almost three), while the other Tigers only have one. Two-tailed is our largest North American Swallowtail (blows "Giant" Swallowtail out of the water), but of course some individuals are larger than others, and they run larger in some regions than others (pretty big generally in e. Colorado). These can be seen from April or May until October, and there are probably about three flights per season (but they aren't well differentiated toward the end of the season).

The Eastern will only be east from the mountains (in theory) and has broader rounder looking wings (subtle, but not hard to see), with the wings proportionately quite large for the body. The under side of the front wings have the marginal yellow band broken into distinct rounded spots (continuous or dark only at the veins in the others). Often the marginal light spot closest to the front edge of the hind wing on the upper side is orange (especially in females), and there is more orange below than is usual than in the previous or next. These can be seen from April or May into October, with more than one flight each summer.

Western Tigers are mostly in the mountains and west (become rare east from the mountains on the Plains). They run smaller than the other two, and look a lot like a smaller version of two-tailed in shape. The front wings usually more pointed and less rounded than in Eastern Tigers, and the wings also usually look proportionately smaller in comparison with the body. The dark stripes tend to look a bit wider or at least closer together than in the other two. There is often a bend in the markings along the outer margin near the tip of the wings. Unlike the previous two, there is usually only one flight (in spring or into summer up high), but in the lower towns where it is warmer and there is a good food supply, they do sometimes fly again later in the summer.

Pale Tiger Swallowtails tend to look white when flying (there is usually a tinge of yellow, but not bright like the ones above, or in a rare individual the color is pale creamy yellow) with the dark stripes wider and bolder than in any of the previous. They are very like Western Tigers, but the front wings are usually even a bit more pointed looking. These almost never stray from the mountains. They also usually fly mostly in spring or early summer, and rarely later.

The adults are easy - compared to the caterpillars and pupae!

David,
Thank you so much, this is excellent.

Thank you for taking the time to convey this information. I really needed the tips too! Diane

Andrew please see the comments for the other swallowtail image I posted the same day:

I lived on the front range for 4 years, and to my knowledge never saw an eastern swallowtail. I spent a ton of time doing insect photo on the greenbelts in Jefferson County. That combined with first looking at the data map for Eastern swallowtail here on Bugguide, which is still white vs. gray, led me to believe that the Easterns didn't extend to the edge of the Rockies. I should have looked down at the BG state list vs. the map. I don't know why CO isn't gray for Eastern. Maybe it takes records in more than one location. Anyway, I stand corrected, and congrats on your CO record for Eastern :-)

If you looked at the map recently, then the image of the map may need a refresh to change the picture. The text seems to update on its own more easily (less caching somewhere).
Remember the maps contain the disclaimer "The following data is based on images submitted and identified by contributors. Range and date information may be incomplete, overinclusive, or just plain wrong." for a reason, we are slowly building the map so just because a state isn't shaded doesn't mean the bug isn't there, it may mean that we just don't have images YET.

I must have looked at that map previously and browser cache not updated. Manually doing it got it shaded. I'll stick to the lists below to be safe. I know our maps aren't the most accurate, but I'm unaware of another mapping tool such as we have here. I don't think books can be trusted either. Climate changes will have species on the move no doubt, and the spread of invasive species over time is readily apparent. Anyway, thanks for the note on cache. I need to watch that.

collection data from the past may have just been too limited. We have 34214 contributors, in many cases that has to beat a handful of grad students with sweep nets.

You probably did see a white CO on the map, since the record just got posted yesterday for the Eastern Swallowtail. I have worked in the same gardens for over 20 years, and I have never seen a black swallowtail here before!