Hiding in Plain Sight

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So I had always just called the Giant Swallowtail’s species Papilio cresphontes. Afterall that is what is my Kaufmann butterfly guide from 2003 calls the Giant Swallowtail. But as we all know, science marches on. In 2014, a paper came out titled “A new Heraclides swallowtail (Lepidoptera, Papilionidae) from North America is recognized by the pattern on its neck”.

This was the butterfly that got me looking further! Or as they say going down the rabbit hole. 😉 And it was an Eastern Giant Swallowtail! So in fact this is now the Heraclides cresphontes or Eastern Giant Swallowtail. Of course I did a search of my photos to see if I had any of the new species, the Western Giant Swallowtail (Heraclides rumiko).
First I will hit the points of the Eastern Giant Swallowtail. Here is the break down of the key morphological points. Below I will refer to the Eastern Giant Swallowtail as Hc and the Western Giant Swallowtail (Heraclides rumiko) as Hr.
  1. As the paper’s title says this is the strongest point. Hc ‘s thorax has spots or just few to almost none. Hr has a solid line.
  2. The Hc abdomen often has a solid black band. Hr usually fainter.
  3. Hc spot variable from smaller to absent on the yellow. Hr has a larger black spot.
  4. Hc much stronger than marginal yellow spots at the dips in the veins. Hr smaller or absent.
  5. Hc has usually larger and more than 3 spots (hard to see the fourth spot in pic). Hr smaller and rarely more than 3.
  6. Hc tail usually shorter, rounder, and wide. Hr narrow and longer.
An additionally morphological different is on the hindwing. Hc inner edge of the black discal band is broken and curved as shown by the red lines. Hr will be straight all the way across.
Now I wish I had a photo of the Western Swallowtail, but nope. However Kathy has two observations on iNat. This one shown here (Oct 9, 2021). If you can zoom in you can see the solid lines on the neck, only 3 spots (area number 5 above), and the tails do look thinner. The black spot closely matches number 3 above.
Next the underside of the second one from Sept 23, 2023. The red shows how it was straight and not broken. Oh yeah the red line is curved but that was from the angle of the shot. Thus it was the sum of the parts that makes this a Western Giant Swallowtail. Please note I added the red lines and text to Kathy’s pics. 🙂

“A combination of characters should be used for reliable identification… Many specimens in central Texas exhibit intermediate characters, atypical character combinations, and possible hybrids can be found.” Additionally the paper says the genitalia was different. Furthermore the COI DNA had a 3% different in the two species. And apparently that 3% is huge. If you would like to read the paper for yourselves it can be found at Shiraiwa K, Cong Q, Grishin NV (2014) A new Heraclides swallowtail (Lepidoptera, Papilionidae) from North America is recognized by the pattern on its neck. ZooKeys 468: 85-135. https://doi.org/10.3897/zookeys.468.8565

A closeup the spots on the neck with spots on the Eastern Giant Swallowtail!.

There is a nice range map of the two species on page 112 of the paper. The Western Giant Swallowtail should not be in Wise County. Indeed, some day I will spot a Hr (Western Giant Swallowtail) when I go south or west.

So there were two species hiding in plain sight! Isn’t that cool!

And thanks Kathy for your two sightings!

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11 Comments

  1. Wow that is really neat. Thanks for the mark ups and details that distinguish them. I wondered what fun stuff you wanted my photos for. Thanks for digging in so deep for us.

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  2. Wow, this is such helpful information! I had noticed that suddenly (it seemed) folks were starting to occasionally ID giant swallowtails on iNaturalist as H. rumiko. I’ve had no idea how to distinguish them, so I stopped making IDs of the giants. Thanks, Mary!

    Sad news about Condor 1K. 😔

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  3. The invertebrate detective strikes again with all the evidence in hand! So cool! Reminds one of keying out the tiny differences between two similar plant species.

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  6. Ditto what Suzanne said. I had stopped identifying Giant Swallowtails and I’m thrilled to have data to back up ids now! Thank you Mary!

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