Eastern Tiger Swallowtails, Canadian Tiger Swallowtails, Hybrids

How do you tell them apart? Can anyone link to a useful site? I have to admit, despite looking up some information and gazing steadily at several specimens, I don’t see much difference. I know there’s a size difference between Canadian and Eastern, but what about the hybrids? I ask because I just had a swallowtail identified as a hybrid on BAMONA, and I am now curious.

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One thing I’ve noticed is looking at the uppersides the blue border on the hindwing is narrower and the bordering black curves are thicker for P. canadensis compared to P. glaucus.

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Ok I’m not so sure now, I just saw some observations that contradict my above statement.

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Sorry for spamming, but this may be useful: https://www.researchgate.net/publication/316654617_Papilio_canadensis_and_P_glaucus_Papilionidae_are_distinct_species

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My copy is locked up at work at the moment, but “Butterflies of Pennsylvania” has a well-illustrated 2-page section on how to distinguish between Eastern, Appalachian, and Canadian Tiger Swallowtails; don’t remember if they talk about hybrids.

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Thank you. I’ll look for a copy on Amazon. Sounds like a guide I should own.

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Thank you for the link!

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I like it! Well-illustrated, good information on food plants and flight times, and has a number of exhibits like that one to help explain certain difficult-to-separate taxa.

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Be very careful about the geography of the reference records. I live in an area in Ontario where apparent hybrids have been found. Now the curator of the Ontario butterfly marks any individual that shows any potential sign of Canadian Tiger as a hybrid.

The result is no records of Canadian Tigers within at least 100 kilometers of here. Yet I’m no biologist but I kind of thought to get a hybrid you needed one of each to start with.

So how we get these is something I cant follow…

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I don’t know the specific case for that region, but I study hybrid speciation and what you often get when two closely related species come into contact is a hybrid zone. Within this hybrid zone if the hybrids are not sterile you can get a whole mosaic of multi-generational hybrids (hybrids crossing with hybrids). If the hybrid zone is wider than the distance that an individual would normally disperse, then you might end up not getting many “pure” individuals moving into the centre of the hybrid zone, and will only find hybrids. The species Papilio appalachiensis in the Appalachian Mountains apparently probably evolved from a Papilio canadensis x glaucus hybrid swarm. So it could be that in your region there really are only hybrids (I think 100 km is pretty wide for a hybrid zone though!)

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That’s fascinating. Thank you.

For Ontario observations, a new report by Chris Schmidt of Agriculture and Agri-Food Canada in Ottawa treats the “hybrids” as not being hybrids at all, but instead a possible new species (B. Christian Schmidt, “More on Ontario Tiger Swallowtails,” in Toronto Entomologists’ Association, Ontario Lepidoptera 2019, April 2020). The working name is “Midsummer Tiger Swallowtail.” Research is ongoing, but molecular markers and diagnostic characters have been found. The report is posted at https://www.ontarioinsects.org/publications/Summaries/2019_tigers.pdf .

The key take-away is that observers in Ontario should take pictures of the underside of the wings and/or the male claspers. Uppersides are not of much help.

The size of the Midsummer Tiger is reported as “intermediate-large”, while Canadian is “small” and Eastern is “large.”

I have written a summary of this report for butterfly watchers and posted it at:
https://www.ontarioinsects.org/tigers.html

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