Naturespeak A naturalist's view of the world

August 18, 2009

Dog Day Foresight

Filed under: Uncategorized — wykes @ 7:37 pm

I really can’t imagine what any given Polyphemus caterpillar is thinking at any given moment. I’m pretty sure that a majority of their microscopic ganglia are firing off  food thoughts, however. There is simply no room for lust, politics, or soduku in their tiny infantile brains (not that the first two take up that much space). As larva, they have nothing else to do but eat. That is their job.  They begin life as 3 mm midgets and complete their task as  3 1/2 inch emerald green gummie giants (see above and below). It takes a solid month of munching hardwoods, lots of pooping,  and four changes of skin (five “instars”) to get there, but get there they do. “There” is a place called the dog-days of summer. It is at this time that this caterpillar begins to think thoughts beyond this time. His thoughts turn to winter even as the mercury plays around the 90 degree mark.

Even though it may seem a bit early to roll wintery thoughts about ones head capsule, the late summer Polyphemus is forced to consider his future. His time as a ‘piller ending, he must now answer those internal hormonal messages that say “build it and change.” He instinctively “knows” to build a weatherproof chamber in which he can pupate. The calendar and the temperature are meaningless in this regard. It is instinct and the ticking of an internal clock which prompts him to begin weaving strands of brown silk to loosely bind a few leaves together. These same leaves which were considered food but a few days before, are now viewed as mere structural supports. The time for eating is done.

      

The only immediate thing that guides the cocoon-making activity of the late summer Polyphemus is the setting sun. He waits until evening to begin the task. It takes a good part of the night to complete the job. Miles of silk, issuing from a pair of spinnerets located beneath his mouth, are laid out in increasing tighter patterns until a tight oval waterproof case is constructed. The silk dries into a firm casing having the texture of grocery bag paper. Finally, a milky white secretion is introduced into the casing and the cocooning part is done. Internally, the caterpillar sheds his skin one more time and converts into a brown Buddha-like pupae and begins the long wait until next summer.

Sometime later this fall the cocoon will likely  fall to the ground as the attached leaves turn color and take a fluttering flight ground-ward. This too is was anticipated. The caterpillar only attaches a few light threads to the branch itself. Other great silk moths, such as the Cecropia and Promethea moths, deliberately attach their wintering structures to the branch, but not the Polyphemus. Once on terra-firma, the cocoon and its resident Polyphemus pupae, will be buried by a protective layer of leaves.

Maybe it’s not right to call all this early preparation an act of foresight, since that implies some thought process on the part of the ‘piller, but it is instinctive foresight. Instinct is the cumulative thought of a million generations, so it tends to be right… most of the time.

1 Comment »

  1. Obviously I’ve just discovered your blog and am going through it post by post. I got a good chuckle out of this one, especially the bit about soduku.

    Comment by Ellen — August 28, 2009 @ 3:46 pm

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