Canadian Tiger Swallowtail

2013 April 24

Sometimes specimens just fall into your hands. On June 22, 2012, I came home and Sam presented me with this nearly perfect Canadian Tiger Swallowtail, Papilio canadensis

It had apparently died of old age, after living a fairly uneventful life that left its wings practically unscathed. It was in much better shape than the one I posted way back in 2009, which had been hit and killed by a car, so this time we can look at the underside.

It still had all six legs, too. Incidentally, we can see that in spite of general resemblance, swallowtails are not in the same family as the “brushfooted butterflies” like monarchs (which have their front legs reduced to little “brushes” that they no longer use for walking).

I’m pretty sure this is a female, because the males have a broader black-and-purple patch at the trailing edge of the wings. Also, the tip of her abdomen looks like it is adapted to laying eggs.

And, here’s the underside of her head, showing the proboscis that she used to uncoil to drink nectar from flowers.

As colorful as most Swallowtail butterflies are, I rather expect that they are at least somewhat distasteful, and that the yellow is a warning color[1]. Although, they are pretty hard to catch (Sam tried to catch one alive with a butterfly net for most of the spring and early summer, and couldn’t do it), so they may survive predators by sheer speed and maneuverability.

[1] A while back, someone asked me what grounds I have for saying that one insect is brightly colored as a warning to predators that it tastes bad or is dangerous, while another is brightly colored because it is making a display to attract a mate. How would we tell one from the other? Well, my general rule of thumb is that if only one sex (usually the males[2]) is brightly colored, then it is probably a mating display. Particularly if the other sex is colored to be highly inconspicuous. But, if both sexes are nearly identically colored, then it is probably a display to warn predators that they taste bad, are toxic, or sting. And, since both the male and female Canadian Tiger Swallowtails look practically identical, I expect that this is mostly a “warning coloration” situation.

[2] And why is it the males that are the brightly-colored ones in these cases? Probably because eggs are metabolically expensive. They need to have all of the structures needed to do all of a cell’s metabolic functions, and also need to be large enough to have the energy reserves for developing and hatching, and so females can only make so many of them. On the other hand, sperm are comparatively “cheap” (being little more than a packet of genetic material with some means of moving around). This means that a given male can produce many times more sperm than the number of eggs a female can produce. As a result, there are more males available than are strictly necessary to fertilize all of the available eggs. So, if the male insects take stupid risks (like flying around in gaudy coloring that is impossible to miss) in the name of attracting female attention, then even if a large fraction of them get themselves killed there are still enough to go around, and their deaths have no effect on the population of the next generation. And if the ones that survive their stupid risks are rewarded by being able to meet significantly more females, then they end up fathering a higher proportion of the next generation than their more-cautious brothers. And so the stupid risk can turn out to be not necessarily so stupid after all. Of course, this doesn’t always work. Sometimes the more-cautious males can find other ways to meet the ladies, and sometimes putting on the public display gets all of the showy males eaten. Which is one of the reasons why there are millions of species of insects with wildly varying lifestyles and mating habits, instead of only a few.

3 Responses
  1. Carole permalink
    April 24, 2013

    Like your thoughts about the warning colors vs attracting colors

  2. April 26, 2013

    Now that’s just gratuitously beautiful.

  3. July 7, 2014

    Actually what you have is a male specimen. Females have broader black stripes and also more blue on the hindwings. The structures at the tip of the abdomen are called claspers, and the males use them to hold on to the female during mating.

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