What Should a Clever Moose Eat? by John Pastor

Author:John Pastor
Language: eng
Format: epub
Publisher: Island Press

12.

Tent Caterpillars, Aspens, and the Regulation of Food Webs

The coevolution of aspens, tent caterpillars, and their predators regulates the productivity of much of the North Woods.

Every 10 or 15 years, the North Woods experiences one of its most spectacular population cycles, the outbreak of the forest tent caterpillar,1 or “army worm” as most people call them. But “spectacular” would not be what comes to mind for most people during these outbreaks. The most common comment would be something like “Yuck! The army worms are back! I hate those things!” At this point, the Minnesota Department of Natural Resources and the U.S. Forest Service get irate calls along the lines of “When are you going to spray these disgusting bugs?” You would think that we are Pharaoh and his people enduring a plague of locusts covering the land.

Our culture has a gut-wrenching aversion to insect outbreaks. Perhaps this is because civilization began with the invention of agriculture, which was, until recently, helpless against epidemics of locusts, grasshoppers, and other insects. Crops made the food supply more reliable, but famine usually followed when the locusts consumed the crops, so we think any insect outbreak is bad anywhere it happens. Although we don’t obtain food from aspen stands, we still emotionally feel that we must save the forest from its “enemies.” But as apocalyptic as these natural outbreaks of tent caterpillars may seem, the forests have always managed quite well without our help.

The forest tent caterpillar, a native species, defoliates large blocks of aspen in late spring or early summer, after the emerging leaves are well on their way to filling out the canopy, leaving them gray and leafless, as if November had made a premature return. If you walked into one of these defoliated blocks, which can be several kilometers long, you would see hundreds of caterpillars arrayed on the trunk of virtually every aspen tree. Despite their bad rap, these are really beautiful caterpillars, about two inches long and dark chocolate brown, with white spots and yellow and iridescent blue stripes along their sides.

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