The Oak Caterpillar - Songbird Connection
Ro Wauer, April 18, 2004 The Victoria Advocate, © 2004
There is a well-accepted ecological principle that states: "Everything living and nonliving is related to or connected to everything else." Also known as the "web of life" and generally defined as whatever man does in the natural world, it causes extensive reactions that usually extend beyond those that are expected and observed. There has been a fascinating example of these interrelationships played out in many of our yards this spring.
The recent example involves the much greater than normal emergence of caterpillars, actually oak leaf rollers and a few other species, in our live oak trees. Their abundance this year, probably due to a mild winter with abundant rainfall, has created an amazing response from land-owners that cannot put up with the abundant caterpillars hanging from silken threads. It is like something out of a horror movie, when creatures from outer space threaten our very existence. An amazing reaction to tiny creatures that are harmless to humans. Sure they are a nuisance, they practically defoliate some of our trees, and the frass (scat) makes a huge mess on our driveways and decks. But it only lasts a couple weeks.
Oak caterpillars, oak leaf rollers as well as inchworms and a few other species, occur in spring just when the migratory birds are passing through South Texas. They provide an enormously important food supply for those songbirds and other species that may have just flown 550 miles across the Gulf of Mexico from Mexico's Yucatan Peninsula the previous night. Without such an immediate supply of nutrients many of our birds would not survive.
Most of my neighbors in response to the almost overwhelming number of oak caterpillars this year sprayed their trees. Most used pesticides that killed every kind of caterpillar, whether oak caterpillars or various butterfly caterpillars that the spray contacted in both the trees and in the fallout area. I did not spray my yard, although I admit I was tempted. Immediately after the spraying the number and species of butterflies in my yard declined dramatically from what they were just prior to the spraying. But, on the other hand, I discovered that the number of migratory songbirds that were present in my yard were considerably greater than in adjacent yards. Their food supply was far more abundant in my yard than in the yards that had been sprayed.
As for the butterflies, the only species found in my yard after the spraying were wanderers, such as giant swallowtails, cloudless and large orange sulphurs, and monarchs. These apparently flew in from elsewhere not subject to the spraying. The more local species that hatch out in and adjacent to my yard, such as gray hairstreak, dusky-blue groundstreak, rounded metalmark, and coyote duskywing, disappeared totally. I am not sure at this writing how long it will taken before my butterfly numbers build back up.
What about the oak trees? How will they do after such a severe outbreak of oak caterpillars? Because the defoliation process is early in the growing season and, although some trees may be weakened, the majority will adequately recover. A recent post on Tex-Butterflies, submitted by Parks and Wildlife Entomologist Mike Quinn, explained that the "defoliated trees are temporarily subjected to reduced productivity (less growth) but they usually experience increased productivity later as a result of a large percentage of their leaves having been converted to frass." Mike also mentioned a recently released fact sheet (No. E-206) on the subject, available at http://tcebookstore.org.
There is no doubt that our natural environment is one huge web, like that built by a spider, and subject to much damaging activity. Each strand effects all the others. In most cases the spider can rebuild its web, and we can continue to use pesticides to address what we perceive as negative impacts on our personal environment. But each year the incidents of cancer and other life-threatening problems increase. At what point will we accept and live with the natural processes? Another ecological fact is that nature always will win in the end!