Day 344: After much digging into books and the internet, and consideration of the butterfly species known to occur in the specific area, I am tentatively identifying Spike as the caterpillar (fifth instar) of Speyeria cybele, the Great Spangled Fritillary. Again, we have a taxonomic readjustment. Formerly called Argynnis, members of this group of North American fritillaries have been distinguished from the European genus with their own nomenclature. Update your field guides, folks! And as always when venturing outside botany (and sometimes within it), I reserve the right to be wrong. Butterflies and moths are not my long suit.
In any event, when Spike is all growed up and his/her wings have come in, he will nectar on members of the Violet family, notably our common Viola rotundifolia. Or that's the plan, anyway. Those of you who have Buddleia (Butterfly Bush) in your yards because "the butterflies love it" are doing more harm than good. Great Spangled Fritillaries are drawn to Buddleia like kids to candy, but it doesn't sustain them any more than a diet of chocolates and butter-mints would a human. Not only that, if the butterflies fail to nectar on the Violas, pollinating them in the process, then there will be fewer Violas to sustain the Fritillaries who haven't discovered butterfly-bush smack. Planting non-native species in your "butterfly garden" is a Bad Idea. Plant natives instead, those things which are known as hosts or food for species in your area. There's a circle here, people. Stop messin' with things you don't fully understand.
