Wednesday, August 6, 2014

Great Spangled Fritillaries

If you have any native flowers currently gracing your Montana habits, then maybe you've noticed the frequent aerial chases between orange and black butterflies. Here's a secret - that isn't competition for food, it's the age old chase for a mate.

Female (top) and male (bottom) Great Spangled Fritillary butterflies (c) John Ashley
Female (top) and male Great Spangled Fritillary butterflies
They fooled me into thinking there were two different species not wanting to share the same flowers. But in reality, the dark ones are females and the orange ones are males of the same species, Great Spangled Fritillary butterflies (Speyeria cybele). Males hang out in open areas, looking for females to chase after - sort of like college town bars during spring break.

This late-summer courtship is just about the only time you'll ever get to see this secretive species, because the camera-shy adults are extroverts compared to their mysterious young caterpillars.

Adults nectar on lots of different flowers, including the thistles and beebalm in my yard. But the females seek out one specific flower family when it's time to lay eggs - wild violets. Later this month, each female will lay up to 2,000 eggs close to the ground, near (but seldom on) violet plants, and the first instars hatch out 2-3 weeks later.

The young caterpillars drink a little water but don't eat for 7-8 months. Instead, they burrow down into the leaf litter and enter diapause, a state of rest for the winter. Come spring, they climb back above ground to eat the fresh, new violet leaves and flowers - but only during the cover of darkness. By day they burrow back down below ground, away from the violet plant.

Is it any wonder that you and I have never seen a secretive, nocturnal, ground-dwelling Great Spangled Fritillary caterpillar?

In July the caterpillar anchors itself to the underside of a rock or log to pupate, and the adult butterfly emerges three weeks later. By early August, the largest members of the Fritillary family start chasing each other around the yard like newlyweds, giving us one good chance to see this otherwise modest animal.