Tremendous beauty can be found in the tiniest of things… for who has ever thought to rival that of a butterfly’s wing.
~Kristen D’Angelo
Close up of hind wings of an Eastern Tiger Swallowtail (click on photos to enlarge)
Every few years, we have a population high of swallowtails here in our woods. This year has been exceptional with the greatest numbers of these large butterflies that I have witnessed. This is especially true of our largest (and one of the most recognizable butterfly species) the Eastern Tiger Swallowtail (Papilio glaucus). One reason they are so common for us is that our woods are dominated by one of their primary host plants, Tulip Poplar.
We have a relatively small area that receives enough sunlight to grow wildflowers, and this time of year the primary nectar sources are Joe-Pye-Weed, Ironweed, and Garden Phlox. When I walked up to the house one afternoon a week ago, it reminded me of being inside a butterfly house, with large butterflies drifting all around me and seemingly covering every available flower head. I decided to estimate their abundance, so I went inside and started counting swallowtails visible from the front window and the kitchen window. I was stunned when I finished with a total of 90 swallowtail butterflies! Most were Eastern Tiger Swallowtails, but there were about 6 Spicebush Swallowtails as well.
Joe-Pye-Weed has been the favorite nectar source in our yard – this one flower stem has 6 swallowtails on it (one is hidden on the back side)
I did a quick Google search looking for explanations of these population highs and lows in tiger swallowtails. I discovered that what I am witnessing both here and at work is also being seen this summer up and down the East Coast – an explosive population year for Eastern Tiger Swallowtails. But, my searching yielded no real clues as to why. It seems there are just too many variables to explain these population swings, although most scientists agree that it probably relates to weather conditions that negatively influence populations of the abundant predators, parasitoids, and fungi that prey upon the pre-adult life stages of these butterflies.
The Garden Phlox has been the big draw for butterflies at work (NC Botanical Garden), especially this one patch (there are 7 swallowtails scattered in this photo, but I have seen many more at times)
Whatever the reason, it has been an incredible summer for swallowtails. They are believed to live an average of 3 to 4 weeks as adults, so they are starting to decline a little after a peak a couple of weeks ago.
Below is an introduction to the swallowtails (and one look-alike) that frequent our woodland garden. The next time you venture out, look closely at your butterflies and see which ones are most common in your landscape.
Female Eastern Tiger Swallowtails have more blue on their hind wings than males.
Males may have a little blue in the hind wings, but not nearly as much as females.
And, just to make it more confusing, female eastern Tiger Swallowtails can also be blackish in their wing background coloration. You can often see faint traces of yellow in the wings, especially from the underside. Like our other black-colored swallowtails, this is believed to mimic the unpalatable Pipevine Swallowtails. The black color morphs are generally more abundant in the mountains, where Pipevine Swallowtails are also more common.
Spicebush Swallowtails (Papilio troilus) are recognized by the wash of color on the hind wings. Females have bluish color and male a bluish-green color. Their host plants are Sassafras and Spicebush. They are generally more active as feeders, flapping their wings much more than Eastern Tiger Swallowtails.
I don’t see many Black Swallowtails in our yard as they are more of an edge species. There are plenty at work, especially late in the summer, due to the abundance of one of the host plants, Golden Alexander. They are smaller than Eastern Tiger Swallowtails and tend to have a bold yellow stripe (males). Females look similar to black morph Eastern Tiger females, but they are smaller and the orange spot at the base of the hind wings has a dark spot in the center.
One day I looked out and saw a very active swallowtail with yellow under its wings feeding on the Joe-Pye-Weed. I recognized it as a Giant Swallowtail (Papilio cresphontes).
Ironically, it was almost exactly a year ago that I saw my first Giant Swallowtail in Chatham County. They are large (North America’s largest butterfly) and very active butterflies, making a spread wing shot somewhat difficult.
Pipevine Swallowtail (Battus philenor). Males (photo above) have a brilliant iridescent blue-green color on the hind wings. Females are duller. This species is an irregular visitor to our yard but is easily recognized by its fluttering feeding styles compared to most other swallowtails. Spicebush swallowtails are also active feeders, but appear much larger than Pipevines. As caterpillars, this species sequesters toxins from their host plants (pipevine and Virginia Snakeroot) which are transferred to the adult, giving them some protection from hungry birds and other predators.
My favorite butterfly, the Zebra Swallowtail (Eurytides marcellus). These beauties are found in areas near their host plant, pawpaw. Freshly emerged specimens often have hints of blue on their wings.
Often mistaken for one of our four dark-colored swallowtails, the beautiful Red-spotted Purple (Limenitis arthemis astyanax) is believed to be another mimic of the unpalatable Pipevine Swallowtail. It has iridescent blue hind wings, lacks the wing tails, and has blue dashes or spots along the wing margins. This species is very common in our woods where its host plant, Black Cherry, is abundant.
Many butterflies are now showing signs of aging and the hazards of life in the wild. This male Eastern Tiger Swallowtail is missing part of one hind wing, perhaps a victim of a missed attack by a bird or mantis.
Birds are major predators of the larval stages of butterflies, but I have not seen much depredation on adult butterflies, especially of our larger swallowtail species. On two occasions, we have seen flycatchers like Eastern Wood-peewees and this Great Crested Flycatcher snag a butterfly in flight.
Large Robberflies are reaching their peak population about now and I have seen them hit some of the swallowtails that were nectaring at flowers, but have only seen one actually carry a large butterfly off to feed on it. This one has a large Carpenter Bee as its meal.
Large spiders (large orb weavers) are major predators of swallowtails in our yard. I do see the butterflies occasionally escape once they hit a web, but we also see many wrapped in silk in the many webs that dot or yard.
Another important predator of large butterflies are the praying mantids, especially the introduced Chinese Mantis. They wait near flower heads and lunge and grab the butterflies. They must be difficult to see as I have watched butterflies forage on the same flower that has a mantis feeding on one of their cousins.
Roads End Naturalist 
Matt and I were just speculating yesterday on the whys of the tiger swallowtail population boom this year! 🙂
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Yeah, it has really been amazing and I found news articles online referencing similar high numbers in PA and VA this summer.
Hmmmm….. and there was me thinking my gardening skills finally improved a bit, attracting this many swallowtails in the yard this year. Is it just an oustanding tiger swallowtail year.
Thanks, I guess 😉
I’m sure your gardening skills contributed some:)
Great pics and informative narrative, Mike! Saw numerous swallowtails last week at Doughton Park on the BRP compared with their greatly reduced numbers last year.
Thanks, and glad to hear they are abundant up there as well.
Thanks for this timely summary and great pics, Mike. “… just to make it more confusing, female eastern Tiger Swallowtails can also be blackish in their wing background coloration”.
I’ve been seeing a number of these dark (black) butterflies and now have a reference to identify which I’m seeing. I suspect it’s this eastern Tiger Swallowtail — maybe more than one type?
Hey Rich:
Right now, as far as black butterflies go, I am seeing mainly dark morph female eastern Tiger Swallowtails and Spicebush Swallowtails in our yard along with a bunch of Red-spotted Purples.