Tuesday, March 20, 2012

Food for wildlife

Jan van Huysum. Blumen und Früchte

I invite you to look at this floral painting by the Dutch artist, Jan van Huysum, and find the connection between it and the title of this blog. Look carefully and visit the enlarged version.

Signs of feeding insects

After reading Doug Tallamy's book Bringing Nature Home, I began to see plants with new eyes. The main focus of the book is the importance of native plants in sustaining the food chain by feeding insects and, by extension, all the wildlife that feeds on insects. He points out that, fortunately, insect feeding damage tends to be moderate, as long as the natural systems are in balance. Insects make a little hole here, a little hole there on leaves; or eat an entire leaf; aphids sap juices from plants, etc. But the appearance of the vegetation is not greatly affected and most plants survive and prosper despite such attacks.

A leaf roller caterpillar hiding inside a leaf

Soon after I finished the book, I went on a trip to the Great Smoky Mountain National Park. I noticed, for the first time, something that probably nobody else in my group was aware of. Insects had left traces of their feeding just about everywhere. But, just as Doug mentioned in his book, none of the damage was serious. I saw little holes grouped together, larger holes on other leaves. I saw leaves with nibbled out edges. I saw leaves with translucent spots where the insects had scraped the nourishing in-between tissues, leaving only the outer surface of leaves. I also saw some skeletonized leaves, where only the inedible veins remained. There were some sap-feeding insects here and there, leaf roller caterpillars, interesting galls.

Sometimes I saw a caterpillar hanging from a thread, probably fully grown and ready to bury itself underground to pupate. I know that, for a caterpillar to reach full size, it must have eaten a handful of leaves. I also know that where I see one caterpillar there may be dozens cheerfully disposing of many leaves. So I looked at the canopy and couldn't detect any damage. The foliage overhead was luxuriantly rich and full.

So, it is quite true, the forest feeds the insects and they, in turn, feed all kinds of creatures, big and small. Birds, squirrels, chipmunks, frogs, toads, and lizards take advantage of this rich protein source. Even bears gobble up caterpillars. As long as the ecosystem is healthy, with a good balance of native plants and native animals, you seldom see serious damage. This balance can be disrupted by non-native plants. If they are indigestible to native insects, they suffer no damage; but also they fail to become part of the food chain. They provide no service to the ecosystem that supports them.

Dead hemlock trees

The ecological balance can also be altered by non-native plant feeders, and we saw an example that same day. We arrived at a grove of hemlock trees where the situation was dramatically different. The stately trees ere reduced to skeletons, devastated by a pest. Some were already dead; others were dying. An insidious insect from Asia, the hemlock woolly adelgid, has been accidentally introduced in eastern North America. In its native land this tiny, aphid-like insect causes only moderate damage to the Asiatic hemlocks. The natural resistance of the host plants and other natural controls keep nature in balance. But in this continent the checks and balances are missing; so the adelgid can become a pest that devastates the defenseless trees.

Getting back to the floral bouquet, Dutch artists of the sixteen and seventeen centuries loved to include insects and other small animals into their flower arrangements, not just pretty butterflies but other less popular creatures. They were realistic to the point of showing blemishes on leaves and fruits and also some of the makers of that minor damage.
Jan van Huysum (detail)
 Here is a detail near the bottom of the above painting: a caterpillar on a half eaten leaf. Another example of partially eaten leaves is shown on Balthasar van der Ast's "Still Life with Flowers, Fruit, and Shells"

Balthasar van der Ast. Still Life with Flowers, Fruit, and Shells

You can see the uncropped painting. Then amuse yourself searching for caterpillars or signs of insect feeding on the following Dutch paintings: 1, 2, 3 and 4.

Afterwards, take a walk in the forest and look for similar signs in the foliage. I don't regard them as blemishes any more because they are important components of the web of life. Visualize the caterpillar that made the holes and imagine a parent bird catching the caterpillar to feed its hungry brood.

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© Beatriz Moisset. 2012

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