Early Fall Nature in the Blue Ridge

September 13, 2018

Nature Notes by Bill Dunson

As summer progresses into early Fall we can see additional signs of the changing seasons. From my bedroom window I observe that the whitetail deer “twins” continue to grow although they still have their spots. Their grazing in our wildflower garden is definitely a concern since the impact of deer herbivory in the adjacent forest is severe. So far they have only eaten one of our cherished plantings. But I will place cages around those plants that I expect to be heavily damaged during the winter.

The impact of grazing is very evident at Bass Lake (Moses Cone Park) where an adjacent cow pasture reveals that only iron weed, bitter/sneeze weed and boneset have escaped the jaws of cattle. It appears that these species are unpalatable and thus they flourish, whereas palatable plants disappear or at least do not flower.

Among many Fall fruits in the forest I especially notice the striking Indian cucumber root, a native lily. The dark fruit is surrounded by red color on the adjacent leaves; this seems to be a classic case of “fruit flagging” whereby the attention of birds is drawn to inconspicuous fruit by reddish leaves. Nearby black gum and Virginia creeper vines utilize a similar strategy to encourage the consumption of their dark fruit by birds.

Changes in the types of dragonflies signal the arrival of Fall. The very distinctive large common green darners migrate south from the mountains and other species such as this autumn meadow hawk begin to be commonly seen. The handsome male widow skimmer seems to be present in both summer and fall. This presumably reflects differences in tolerance to low temperatures and perhaps different diets of summer and fall predators.

One of the major predators of insects is the large golden garden spider. In early Fall the large females are very obvious in their beautiful orb webs. They hang behind the web, along an unusual zig-zag structure called the stabilimentum, which may serve to protect the spider from predation, to protect the web from destruction by flying birds, and/or to attract insects by its reflectance of UV light. These females are doomed to die when frosts appear but their eggs and hatchlings will live to produce a new generation of spiders.

Butterflies become less common in Fall but some southern butterflies, such as this cloudless sulphur nectaring on jewelweed, actually migrate northwards in late Summer and early Fall. This great spangled fritillary is basking with wings fully extended to warm up on a cool morning in the Blue Ridge Mountains. Such thermoregulation can extend the activity period a bit longer than otherwise possible.

Monarchs in our area primarily breed earlier when the milkweed leaves are young and tender. By Fall the abundant common milkweeds are mainly being consumed by milkweed tussock moth caterpillars, which seem to prefer the coarser older leaves. Thus there is minimal competition between these two species and no reason to destroy the moth caterpillars.

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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