Fire and Water in the Blue Ridge

Late June is a great time for a natural history ramble since so much is happening. Birds have been breeding for some time and the first crop of babies is out of the nests. For those birds which breed in our nest boxes (bluebirds and tree swallows) we are quite aware of the progress of breeding. The tree swallows are almost finished with nesting since they have only one brood in this location. On the other hand, bluebirds have fledged one brood and are sitting on a second set of eggs. Some of our more cryptic breeders such as the warblers are heard often but we know very little about their nesting. For example every single day I hear a number of Kentucky warblers singing (see photo), and they do so all day long. They like our forest gaps and valley edge habitats.

We have three types of magnolias in our forests, cucumber tree, tulip poplar, and Fraser magnolia. I am partial to these trees since they are an ancient lineage that have large beautiful blossoms attractive to nectar-feeding birds, and produce large red berries later for birds and mammals to enjoy. Their excellent contribution to wildlife habitat is not often appreciated. The Fraser magnolia has an interesting arrangement of leaves in its saplings (see photo). The leaves do not overlap at all in this photo which illustrates how such a pattern avoids competition for light between leaves, at least in this first whirl.

I noticed a disturbance in one of our small ponds and found two snapping turtles locked in battle (see photo). At first I thought these combatants might be mating, but the ferocity of the battle with repeated bites to the head and feet of the other turtle led me to speculate that this was a territorial squabble. Since male and female snappers are quite hard to differentiate without measurements of their tail length, I cannot determine the sexes involved.

Our elderberries have done extremely well this year- they escaped severe damage from deer and Japanese beetles last year and thrived. Perhaps in consequence they have attracted another herbivore which is very striking in coloration, the elderberry longhorn beetle or borer (see photo). The picture does not do full justice to the brilliant iridescent bluish sheen of the rear portions of the wing covers and how this contrasts with the yellowish areas. Clearly this beetle is advertising itself as noxious and warning birds not to eat it. Apparently it is deriving its poisonous nature from the toxins in its food, elderberry shoots and roots.

A small beetle that I encountered near a pond was colored in yellow and black and at first I was sure that it was a bombardier beetle, which is famous for discharging a toxic secretion from its rear when disturbed. However on closer inspection I realized that it was a soldier beetle which strongly resembles the bombardier, probably due to mimicry. It also resembles a firefly, another beetle which is distasteful to bird predators.

An additional example I found of a toxic insect advertising itself is a caterpillar of the pipevine swallowtail butterfly (see photo). This larva was feeding on the leaf of a pipevine, which contains toxins which are held in the body of the caterpillar and subsequently also protect the adult butterfly (see photo). The pipevine butterfly is widely mimicked by other swallowtails (such as the black tiger female, the spicebush swallowtail, the red-spotted purple, etc.). I had never read that the caterpillar itself was also mimicked but when I found the caterpillar of the great spangled fritillary butterfly (see photo) I immediately noticed that it strongly resembled the pipevine caterpillar, except for its spines. Yet the adults have no similarity at all (see photo of fritillary adult on echinacea).

When you begin to identify some of the common insects which swarm around us in amazing numbers, you will immediately notice a lot of mimics. What does this mean? It tells us that protection from predators, mainly birds, is a huge feature of survival. It should be no surprise that it is easier to teach a bird not to eat a certain toxic insect if it resembles another one which is also toxic (Muellerian mimicry). There can be combinations of bright or striking contrasts in colors which indicate toxicty and which predators learn to recognize in a generic sense. There are also a considerable number of mimics which are tasty and resemble toxic model species (Batesian mimicry). The intricate nature of these patterns and resemblances is so stunning that it is a remarkable example of evolution based on selection by predation. Birds apparently do a very thorough job in searching for edible insects and it must take a close resemblance between a model and a mimic for them to be fooled.

Bill Dunson, Englewood, FL & Galax, VA
wdunson@comcast.net