Have you ever seen a caterpillar hanging from a thread when you were walking through the woods? You probably have, more than once; it happens often enough that, although caterpillars are very small and not easy to see, everybody sooner or later gets a chance to see this peculiar scene.
Did you ever wonder where it was going? Certainly not up, most likely down. But, down where and for what reason?
Many caterpillars feed high on the canopy, devouring tender leaves and growing very fast. After they are done growing they start getting ready for the big transformation, called metamorphosis, which will turn the rather shapeless, wormy thing into a winged marvel, a moth.
Where you find a caterpillar there may be hundreds or thousands, all of them gleefully feeding on the same tree. Look up at the tree’s foliage above your head; there doesn’t seem to be much damage and this is very fortunate. Part of the reason is that there are many hungry creatures who regard the caterpillars as very tasty and very nutritious morsels of food. Among them you can count some of your most beloved birds, warblers, wrens, sparrows. You see them fleeting about and they may be picking up some of your caterpillar’s brothers and sisters. They will be taking them to their growing brood and ramming them down their hungry throats.
Let us get back to our question: where is the caterpillar going? It may be looking for a secluded place in the leaf litter, safe from winged predators (although not entirely safe for there are other hungry creatures in the soil too). Once on the ground it probably won’t go very far. In most cases it tries to find some leaf litter and it proceeds to bury itself in it. There it will begin spinning a cocoon using a special kind of saliva that changes into silk, strong and supple, as soon as it gets in touch with air.
It may proceed to undergo a big transformation in just one or two weeks to become an adult moth, or if it is the end of the season, it will wait until next year; hunkering down through a long and cold winter and will emerge only when the trees are already leafing out.
During that time it grows wings and legs and antennae and becomes a pretty moth ready to find a mate and to start the cycle all over again. If it is a female it will lay eggs after searching very diligently for the same kind of trees where it fed as a caterpillar.
Most caterpillars are very particular about their food; they can feed only on one kind of tree or perhaps a handful of related trees, for instance, only sugar maples or only several varieties of maples, but not oaks or ash trees. Others will choose only oaks or ash trees. They are so particular that many of the ornamental trees brought from overseas for their beautiful foliage or interesting shape are useless to them. The indirect consequence of a landscape with only imported plants is: no caterpillars - no food for the birds. If you love birds you may want to plant native trees to ensure that birds can find food hidden in their foliage.
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