27 September 2010

A Fen-tastic Saturday Morning, Part III

In my previous two posts, I discussed the plant communities and some of the plants present in three of northeastern Indiana's highest quality fens. While botanizing these preserves, Nate Simons and I noticed a few common butterflies and moths that certainly deserve a place on this blog.

In the photograph above, a Monarch (Danaus plexippus) is feeding on nectar from Spotted Joe-Pye Weed (Eupatoriadelphus maculatus). Monarchs are protected by chemicals they obtain as caterpillars that are toxic and taste bad to potential predators. These heart toxins come from milkweeds (Asclepias spp.), and are often many times stronger in the Monarch caterpillar than they are in a milkweed plant.

While most people are familiar with the phenomenon of bird migration, relatively few are aware that millions of Monarchs depart on similar journeys each fall and spring. Many of our butterfly species overwinter as adults, caterpillars, or pupae; however, our winters are just too cold for Monarchs, so they annually travel south (some up to 3000 miles!) at the end of our warm season. Monarchs who have summer homes in eastern North America all travel to the Sierra Madre Mountains in Mexico, whereas those in western North America make their way to California. To stay warm during their migration and during the winter, congregations of up to tens of thousands of Monarchs cluster together on a single tree. I hope to someday visit the Sierra Madre Mountains in February to see this amazing sight. As seen on the Journey North webpage, this year's Monarch migration is already underway!

The most amazing part about this migration phenomenon is that the butterflies that migrate this year are several generations removed from those that migrated last year. Once Monarchs return back to North America in the spring, they lay eggs in March and April and then die soon after. Those eggs eventually develop into caterpillars, then into adults that lay eggs and then die. The next generation hatches in May or June, and the next generation after that is born in July or August. Finally, after all of these adults have lived their short lives, another generation is born in September or October. It is this generation that migrates, hibernates, mates, then migrates back to North America to lay eggs and die. One of the great mysteries of our natural world is how the migrating generation of Monarchs knows where to go each fall, as it was their great-great-grandparents, who died several months earlier, that last made the long journey to Mexico or California.

After reviewing the fritillaries in several of my resources, I came to the conclusion that the butterfly above is an Aphrodite Fritillary (Speyeria aphrodite). On another of my photos, the silver spots on the hindwing undersides of this butterfly are conspicuous. Aphrodite Fritillaries have only a single brood each year, with adults typically present from June to September. Eggs are laid in the late summer and caterpillars hatch in the late summer or early fall. The caterpillars then overwinter and begin feeding on violets (Viola spp.) the following spring.

Question marks and commas aren't just forms of punctuation, you know. In fact, they are both species of butterflies. The butterflies going by these names are also quite similar in appearance. When looking at the upper surface, the two species can be distinguished by looking for an extra dark spot on the forewing present in Question Marks (Polygonia interrogationis) but not in Eastern Commas (Polygonia comma). This extra spot is the horizontal rectangle near the top and outside edge of the forewing on the Question Mark shown above.

Another way to tell a Question Mark from an Eastern Comma is to look at the underside of the hindwing, where each species bears the tiny silvery punctuation symbol for which it is named. As seen above, this butterfly is therefore a Question Mark; an Eastern Comma would lack the dot underneath the comma on the underside of the hindwing. Another way to tell the two similar species apart is that Question Marks have longer hindwing tails than do Eastern Commas.

In addition to feeding on nectar from flowers, Question Marks also feed on tree sap, decaying fruit, animal droppings, and carrion. They often overwinter as adults.

The first three species highlighted in this post are butterflies, but the caterpillar above is that of a moth. Specifically, this grayish-green larva is the caterpillar of the Hitched Arches Moth (Melanchra adjuncta), feeding on leaves of Ohio Goldenrod (Solidago ohioensis, or Oligoneuron ohioense). Thanks to Ben Hess of Ben and Joy, who let me know that Janet Creamer of Indy Parks Nature Blog and Midwest Native Plants, Gardens, and Wildlife had identified this caterpillar for him just a few weeks ago. And thanks, Janet!

That wraps up my account of my visit to some of the fens of northeastern Indiana this September. As you can see, these unique communities are home to a nice variety of unique plants and animals, but my reports barely scratch the surface.


ben said...

Scott, I had the same caterpillar ID problem. Janet Creamer figured it out for me. Melanchra adjuncta, Hitched Arches; see what you think.

Scott Namestnik said...


Keith said...

Very good posts, Scott, and very educational!

Scott Namestnik said...

Thanks Keith!