Once in a while, if you are traveling on dirt roads, you may come across a cluster of butterflies in the road, such as the pictured Canadian Tiger Swallowtails, that are so engaged in what they are doing that you can approach them fairly closely. The butterflies, predominantly males, have gathered to obtain salts and minerals that have leached from the soil into standing puddles and moist dirt. The act of acquiring nutrients in this manner is referred to as “puddling.”
Because butterflies do not have chewing mouthparts as adults, they must drink their meals. While nectar is their main source of nutrition, males often supplement their diet with these minerals. The sodium uptake aids in reproductive success, with the precious nutrients often transferred from the male to the female during mating. This extra nutrition helps ensure that the eggs survive.
Canadian and Eastern Tiger Swallowtails are very similar, and their ranges overlap. To determine which you have seen, look at the underside of the butterfly’s forewing and see if the yellow band along the margin is solid (Canadian Tiger Swallowtail, Papilio canadensis), or if it is broken up into spots (Eastern Tiger Swallowtail, Papilio glaucus).
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Swallowtails are North America’s largest butterflies, and their tropical relatives are the largest butterflies in the world. At this time of year, Tiger Swallowtails emerge from their chrysalises and seek nectar wherever they can find it, often in gardens. The two common species in the Northeast are the Eastern Tiger Swallowtail and the Canadian Tiger Swallowtail. Those of us living in northern New England are most apt to see the Canadian Tiger Swallowtail, which replaces the Easter Tiger Swallowtail this far north. Both species can be found further south. There are ways to tell these two swallowtails apart (although sometimes where their ranges meet, it can be difficult). The Canadian Tiger Swallowtail is smaller than the Eastern Tiger Swallowtail, but unless you have them side-by-side, this isn’t all that helpful. The easiest way to tell the two species apart is to look on the underside of the butterfly’s forewing and see if the yellow band along the margin is solid (Canadian Tiger Swallowtail, Papilio canadensis), or if it is broken up into spots (Eastern Tiger Swallowtail, Papilio glaucus). (Photo is of a Canadian Tiger Swallowtail)