Why Are There So Many Tiger Swallowtails this Year?

Eastern Tiger Swallowtail

Why ARE they so many Eastern Tiger Swallowtails this Year?

This year there are more Eastern Tiger Swallowtails in my garden than I have ever seen before. In years past I’ve seen one, maybe two, Tiger Swallowtails per day in my garden. This year I’m seeing 10, 15, and even 20 at a time in my wildlife garden.

And in every wildlife garden I visit it’s the same there, too. People up and down the East Coast are remarking on this phenomenon, too. And people are submitting this question through the Ask Carole feature here.

So, I decided to find out what was going on. When I have any questions about butterflies I go to my friend and mentor Pat Sutton who is a walking butterfly encyclopedia, and her passion for creating butterfly gardens is infectious.

Pat in turn posed the question to her friend and mentor, David Wright. His response is fascinating:

Same observations have been reported through out Pennsylvania.  I have no explanation. It’s one of the still unsolved mysteries of invertebrate biology. Population fluctuations are natural; they could be the result of internal genetics (as in small mammals like voles) or the could be the result of a bad year for their parasitoids/viruses (more likely).

A simple average temperature increase doesn’t seem to do it. I did do a literature search on the melanic enzyme pathway in dark morph females. It seems that heat cannot create more black females. But the heat can make the black females a more “dusty” intermediate phenotype. Scattered black scales are converted to yellow.

This search was in response to comments on PA-LepOdes that there were more black females being seen this summer, without a substantial increase in Pipevine Swallowtails. After a week these comments ceased. I think we were observing an emergence of a fresh brood that was atttracted to flower-filled in peak bloom. It’s quite impressive to walk through a large meadow in bloom and see 200 swallowtails.

© 2010 Jo Ellen Meyers Sharp

Tiger Swallowtails peak in April/May and again in July/August, although they can be seen anytime from March to October. So it is possible that the large numbers of these butterflies that everyone is reporting is just the result of this normal peak in their population.

But is it possible that the unnaturally cold (and unnatural amounts of snowfall) affected the parasitoids that normally put a damper on the numbers of adult Tiger Swallowtails?

The thing is, there are many questions about nature that scientists don’t yet have all the answers to. But Mother Nature knows what she’s doing, I’m sure. For now, I will just glory in the sight of these beautiful visitors to my wildlife garden.

How about you? Are you seeing a lot of Tiger Swallowtails this year?

[Many thanks to Jo Ellen Meyers Sharp of Hoosier Garden for sharing her "dueling Swallowtails" photo]

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© 2010 – 2012, Carole Sevilla Brown. All rights reserved. This article is the property of EcosystemGardening.com If you are reading this at another site, please report that to us

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About Carole Sevilla Brown

Carole Sevilla Brown is a Conservation Biologist who firmly believes that wildlife conservation begins in your own back yard. Carole is an author, educator, speaker, and passionate birder, butterfly watcher,  and naturalist who travels around the country teaching people to garden sustainably, conserve natural resources, and create welcoming habitat for wildlife so that you will attract more birds, butterflies, pollinators and other wildlife. She gardens for wildlife in Philadelphia, zone 6b, and created the philosophy of Ecosystem Gardening. Watch for her book Ecosystem Gardening, due out soon. Carole is managing editor of  Beautiful Wildlife Garden, and also  Native Plants and Wildlife Gardens. Follow Carole on Facebook and also @CB4wildlife and on Google+


  1. Carole,
    You are SO lucky to see all of those Swallowtails! What a beautiful thing to experience in your gardens and along the East Coast. The response from David Wright is very enlightening, not just for the Swallowtails, but for how different species differ through the years and seasons. Thanks for the lesson!
    Kathy Green recently posted..Sublime Lime Design

    • Carole Brown says:

      Kathy, I’m hearing folks on the west coast saying they’re seeing more, too. Do you have Western Tiger Swallowtails? You might be too high elevation wise. I’m not sure of their range there.

  2. I’ve been noticing the bumper crop of swallowtails, too–not HUNDREDS, mind you, but six or seven at a time instead of one or two, and a good number of the dark morphs. We always get some, having all these tulip poplars around, but it’s definitely an up year. They like the zinnias and the black-eyed susans, and they go absolutely nuts over the mountain mint, which is an underused perennial and brings in the pollinators like nothing I’ve ever seen.

    • Carole Brown says:

      Ursula, I don’t know where David spotted HUNDREDS, but doesn’t that sound absolutely amazing? I’ve got an average of 10 or more in my garden.

  3. How interesting Carole. We too have had an abundance of Swallowtails this year and what a joy to have them visit. Each one an inspiration and delight to watch-what a joy!

    • Carole Brown says:

      I’m so glad you get to enjoy the show, too, Marghanita. Your kids must be thrilled!

  4. I thought this was such an interesting post. I also have tons of them this year, and I thought it was due to planting their larval food everywhere, but now I’m not so sure. Very cool information.~~Dee

    • Carole Brown says:

      Thanks, Dee. It is a mystery because Tiger Swallowtails are generalists. Their caterpillars can feed on a long list of plants: poplar, cherry, maple, sassafras, elm, and willow. Most butterflies are specialists, needing one specific plant or one family of plants on which to lay their eggs.

  5. Carole, I have been thinking the same and asking the exact question. Others have too as you say. I think the lack of rain has helped somewhat for all sorts of butterflies… many more Pearly Crescentspots too… hundreds … so magical walking through the meadows and beds of gooseneck. Our milder winter and near drought must be good for butterflies. ;>)
    Carolflowerhill recently posted..Joyous Fritillary Flutter And Others Fly For Beautiful Bountiful Buddleia

    • Carole Brown says:

      Your winter was MILD? You’re really lucky because ours was way colder with MUCH more snow (almost 7 feet). LOL, it’s always greener….. For me, I’m just content to enjoy the show because a garden full of butterflies makes me so happy!

  6. Mike Korner says:

    Very cool Carole! No surplus of Tiger Swallowtails to report from this yard in Iowa.

  7. Hi Carole, I’ve had a huge number this summer, too…and have been posting on my blog about seeing the eggs, larvae and now loads and loads of swallowtails. No matter HOW they got here or WHY there are more this year, it is beautiful–and a real treat for all of us! It is quite an interesting phenomenon.

    • Carole Brown says:

      Jan, it’s so cool that because there are so many this year, a LOT of people who never noticed butterflies before are seeing them and asking questions. I’m hoping this will create a whole new group of butterfly gardeners for next year.

  8. Hmmm…I was wondering the same thing this summer when we began noticing not only increased numbers, but they also seem larger than in years past! Its indeed a wonderful gift to have their fluttering company keeping us entertained. :-)

  9. Carole, we’ve noticed an abundance of them, too. Also, the Red-spotted Purples are absolutely EVERYWHERE. Unbelievable numbers of those. We had a very mild winter here, so it’s likely not due to that, but for whatever reason, I love going out and being surrounded by so many! I get hit by a “flutter-by” quite often! :-)
    Kylee from Our Little Acre recently posted..Bloom- Crawl- Fly

    • Carole Brown says:

      Well, Kylee I guess we can rule out the weather then, because while you were lucky enough to have a mild winter, ours was abnormally brutal–extremely cold and more snow than we’ve gotten in the past ten years together. I’m really hoping we don’t have a repeat of THAT next year, LOL!

      • We had a fair amount of snow, but for us, that’s usually how it is. Those brutally cold winters don’t seem to produce as much snow for us. I was happy for the snow cover; most of my marginal plants made it through the winter just fine. :-)
        Kylee from Our Little Acre recently posted..Bloom- Crawl- Fly

  10. We’ve got tons of Swallowtails in Denver as well, and we also had a mild winter. Weird!

    Seems like, on the other hand, I’ve seen fewer Monarchs than usual.
    Sonia Simone recently posted..Mud on my Face- and a Marketing Revelation

  11. My theory is that the devastating cold limited the competition for food dramatically. Here in Florida the Gulf Fritillary is the most prevalent butterfly – and I didn’t see any ’til almost mid year – usually they start popping up in January. And they frequent the same plants as Swallowtails…

  12. Yep–I have lots on my butterfly bushes-often up to 8 at a time here in Baltimore. I saw one feeding that had only a portion of its upper wings left! A real trooper!

  13. michele says:

    Thank you for addressing this! Gardening in NYC, I treasure every glimpse of wildlife. This year I thought we’d won the butterfly mega millions! The swallowtails, yellow predominantly, as well as dozens of spring azures, painted ladies, & many others I couldn’t identify. It seems we also have a surge in beneficial insects, including many different kinds of bees. Saw my first sweat bees, & saw them in droves! It will remain one of my favorite gardening memories, this butterfly season, & a lovely reward for our efforts to increase native plantings in our tiny yard.

  14. We have absolutely seen more than ever before. I even made a video of them, before they were in total abundance. They are everywhere, and more black, and some variety of other butterflies as well.

    I have a butterfly fold out field guide out for our guests here at The Claiborne House B&B in Rocky Mount Virginia, they are having a blast seeing them all!
    InnkeeperVA recently posted..Happy New Year!

  15. I usually see one or two, and this year, I’ve seen about a half-dozen, so some increase for me this year. I wonder if there are “edibles” for the caterpillars that have growth more vociferously this year because of the extra rainfall.
    Meanwhile, re: other butterflies: very few monarchs, mainly because the tussock moth caterpillars – black, white, orange and fuzzy – have eaten much of the milkweed.
    Deb Woodell recently posted..4th annual Philadelphia Honey Festival

  16. I noticed that here in 2013 there are more flying over the tallgrass prairie I visit here in Iowa as well.
    In fact it was the first time I’ve ever been able to film one.

    Haven’t seen nearly as many Monarchs this year but quite a few swallowtails!
    Kevin J Railsback recently posted..It’s Important To Get Out In The Field Even If You Don’t Feel Like It

  17. Jane Umstead says:

    It has been wonderful seeing all the swallowtails in central VA, this summer. I will truly miss them when they are gone. They have been very numerous all over our area on the Piedmont, east of the Blue Ridge Mts.
    What is the host plant for Tiger Swallowtails?
    I’m hoping this is a good ecological sign!

  18. Yes, we are seeing more here in NJ. I was wondering if it only seemed like more because there were no monarchs this year, so the swallowtails really stand out. We have a lot of skippers too.
    Nature in the Burbs recently posted..Thistles and Goldfinches


  1. [...] were a LOT of Tiger Swallowtails this year, which was great because I got to study them very closely. Usually I see at most three Tiger [...]

  2. [...] had a banner year for Eastern Tiger Swallowtails this year. Scientists are still uncertain why this year was such a good year for these butterflies, [...]

  3. [...] there, too. People up and down the East Coast are remarking on this phenomenon, too…Find out Why Are There So Many Tiger Swallowtail Butterflies This Year? at Ecosystem Gardening Share this: [...]

  4. [...] Why Are There So Many Tiger Swallowtails this Year? ”This year there are more Eastern Tiger Swallowtails in my garden than I have ever seen before. In years past I’ve seen one, maybe two, Tiger Swallowtails per day in my garden. This year I’m seeing 10, 15, and even 20 at a time in my wildlife garden. And in every wildlife garden I visit it’s the same there, too.” by Carole Sevilla Brown [...]

  5. […] In years past butterflies have been abundant in my Ecosystem Garden to the point where I wrote about Red Admiral Population Explosion and also Why Are There so Many Tiger Swallowtails this Year? […]

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